1 Στούμπος_Δημοσιεύσεις. Περίληψη

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1 1. C. C. Stoumpos, L. Mao, C. D. Malliakas, M. G. Kanatzidis, "Structure-Bandgap Relationships in Hexagonal Polytypes and Low Dimensional Structures of Hybrid Tin Iodide Perovskites", Inorg. Chem., 2016, in press (doi: /acs.inorgchem.6b02764) The present study deals with the structural characterization and classification of the novel compounds 1-8 into perovskite subclasses and proceeds in extracting structurebandgap relationships between them. The compounds were obtained from the employment of small, 3 to 5-atom wide organic ammonium ions seeking to discover new perovskite-like compounds. The compounds reported here adopt unique or rare structure types akin to the prototype structure perovskite. When trimethylammonium (TMA) was employed we obtained TMASnI 3 (1) which is our reference compound for a perovskitoid structure of face-sharing octahedra. The compounds EASnI 3 (2b), GASnI 3 (3a), ACASnI 3 (4), IMSnI 3 (5) obtained from the use of ethylammonium (EA), guanidinium (GA), acetamidinium (ACA) and imidazolium (IM) cations, respectively, represent the first entries of the so-called hexagonal perovskite polytypes in hybrid halide perovskite library. The hexagonal perovskites define a new family of hybrid halide perovskites with a crystal structure that emerges from a blend of corner- and face-sharing octahedral connections in various proportions. The small organic cations can also stabilize a second structural type characterized by a crystal lattice with reduced dimensionality. These compounds include the two-dimensional (2D) perovskites GA 2SnI 4 (3b), IPA 3Sn 2I 7 (6b) and the one-dimensional (1D) perovskite IPA 3SnI 5 (6a). The known 2D perovskite BA 2MASn 2I 7 (7) and the related all-inorganic 1D perovskite RbSnF 2I (8) have also been synthesized. All compounds have been identified as medium-to-wide bandgap semiconductors in the range of E g = ev with the bandgap progressively decreasing with increased cornersharing functionality and increased torsion angle in the octahedral connectivity. Σύνθεση και χαρακτηρισμός των ημιαγώγιμων περοβσκιτικών πολύτυπων TMASnI 3, EASnI 3, GASnI 3, ACASnI 3 και IMSnI 3 και των περοβσκιτών χαμηλής δομικής διάστασης GA 2SnI 4, IPA 3Sn 2I 7, IPA 3SnI 5,BA 2MASn 2I 7 και RbSnF 2I. Χαρακτηρισμός των οπτικών και φασματοσκοπικών ιδιοτήτων των υλικών. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε μονοκρυσταλλικά και πολυκρυσταλλικά δείγματα. Συλλογή κρυσταλλογραφικών δεδομένων και επίλυση κρυσταλλικής δομής. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συγγραφή του άρθρου. 1 Στούμπος_Δημοσιεύσεις

2 2. T.-B. Song; T. Yokoyama; C. C. Stoumpos; J. L. Logsdon; D. H. Cao; M. R. Wasielewski; S. Aramaki; M. G. Kanatzidis, Importance of Reducing Vapor Atmosphere in the Fabrication of Sn-based Perovskite Solar Cells, J. Am. Chem. Soc., 2016, in press (doi: /jacs.6b10734) Tin-based halide perovskite materials have been successfully employed in lead-free perovskite solar cells, but the tendency of these materials to form leakage pathways from p-type defect states, mainly Sn 4+ and Sn vacancies, causes poor device reproducibility and limits the overall power conversion efficiencies. Here, we present an effective process that involves a reducing vapor atmosphere during the preparation of tin-based halide perovskite solar cells to solve this problem, using MASnI 3, CsSnI 3 and CsSnBr 3 as the representative absorbers. This process enables the fabrication of remarkably improved solar cells with power conversion efficiencies of 3.89%, 1.83% and 3.04% for MASnI 3, CsSnI 3 and CsSnBr 3 respectively. The reducing vapor atmosphere process results in more than 20% reduction of Sn 4+ /Sn 2+ ratios, which leads to greatly suppressed carrier recombination, to a level comparable to their lead-based counterparts. These results mark an important step towards a deeper understanding of the intrinsic tinbased halide perovskite materials, paving the way to the realization of low-cost and lead-free Sn-based halide perovskite solar cells. Σύνθεση και φασματοσκοπικός χαρακτηρισμός των ημιαγώγιμων, υβριδικών περοβσκίτων CH 3NH 3SnI 3, CsSnI 3 και CsSnBr 3 και των αρχικών αντιδραστηρίων, CH 3NH 3I, SnBr 2 και SnI 2. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια. Συν-συγγραφή του άρθρου. 2 Στούμπος_Δημοσιεύσεις

3 3. A. G. Kontos; A. Kaltzoglou; E. Siranidi; D. Palles; G. K. Angeli; M. K. Arfanis; V. Psycharis; Y. S. Raptis; E. I. Kamitsos; P. N. Trikalitis; C. C. Stoumpos; M. G. Kanatzidis; P. Falaras. "Structural Stability, Vibrational Properties, and Photoluminescence in CsSnI 3 Perovskite upon the Addition of SnF 2", Inorg. Chem. 2016, in press (doi: /acs.inorgchem.6b02318) The CsSnI 3 perovskite and the corresponding SnF 2-containing material with nominal composition CsSnI 2. 95F 0.05 were synthesized by solid-state reactions and structurally characterized by powder X-ray diffraction. Both materials undergo rapid phase transformation upon exposure to air from the black orthorhombic phase (B-γ-CsSnI 3) to the yellow orthorhombic phase (Y-CsSnI 3), followed by irreversible oxidation into Cs 2SnI 6 within several hours. The phase transition occurs at a significantly lower rate in the SnF 2-containing material rather than in the pure perovskite. The high hole-carrier concentration of the materials prohibits the detection of Raman signals for B-γ-CsSnI 3 and induces a very strong plasmonic reflectance in the far-ir. In contrast, far-ir phonon bands and a rich Raman spectrum are observed for the Y-CsSnI 3 modification below 140 cm 1 with weak frequency shift gradients versus temperatures between 95 and +170 C. Above 170 C, the signal is lost due to B-α-CsSnI 3 re-formation. The photoluminescence spectra exhibit residual blue shifts and broadening as a sign of structural transformation initiation. Σύνθεση και φασματοσκοπικός χαρακτηρισμός του ημιαγώγιμου, περοβσκίτη CsSnI 3. Συν-συγγραφή του άρθρου. 3 Στούμπος_Δημοσιεύσεις

4 4. D. H. Fabini; C. C. Stoumpos; G. Laurita; A. Kaltzoglou; A. G. Kontos; P. Falaras; M. G. Kanatzidis; R. Seshadri. "Reentrant Structural and Optical Properties and Large Positive Thermal Expansion in Perovskite Formamidinium Lead Iodide", Angew. Chem., Int. Ed in press (DOI: /anie ) The structure of the hybrid perovskite HC(NH2)2PbI3 (formamidinium lead iodide) reflects competing interactions associated with molecular motion, hydrogen bonding tendencies, thermally activated soft octahedral rotations, and the propensity for the Pb 2+ lone pair to express its stereochemistry. Highresolution synchrotron X-ray powder diffraction reveals a continuous transition from the cubic α-phase (Pm-3m, #221) to a tetragonal β-phase (P4/mbm, #127) at around 285 K, followed by a first-order transition to a tetragonal γ- phase (retaining P4/mbm, #127) at 140 K. An unusual reentrant pseudosymmetry in the β-to-γ phase transition is seen that is also reflected in the photoluminescence. Around room temperature, the coefficient of volumetric thermal expansion is among the largest for any extended crystalline solid. Σύνθεση και χαρακτηρισμός τoy ημιαγώγιμου περοβσκίτη HC(NH2)2PbI3. Ανάπτυξη πολυκρυσταλλικής σκόνης για περαιτέρω χαρακτηρισμό με περίθλαση ακτίνων-χ. Συλλογή δεδομένων με τη χρήση ακτινοβολίας σύγχροτρου συναρτήσει της θερμοκρασίας. Συν-συγγραφή του άρθρου. 4 Στούμπος_Δημοσιεύσεις

5 5. T. Yokoyama; T.-B. Song; D. H. Cao; C. C. Stoumpos; S. Aramaki; M. G. Kanatzidis. "The Origin of Lower Hole Carrier Concentration in Methylammonium Tin Halide Films Grown by a Vapor- Assisted Solution Process", ACS Energy Lett. 2016, A low hole carrier concentration in methylammonium tin halide (MASnX 3) perovskite semiconductors is a prerequisite for a nonshorting solar cell device. In-depth film characterizations were performed on MASnI3 xbrx films, fabricated by both a low-temperature vapor-assisted solution process (LT-VASP) and conventional one-step methods, to reveal the origin of the lower hole carrier concentration from films of the former approach. We found that the vaporization of CH 3NH 3I solid at 150 C, the temperature at which the LT-VASP occurs, does not supply iodine to the SnX 2 (X = Br, I) films. As a result, secondary phases form aside from the desired MASnX 3 perovskite; the secondary phases are suggested to be SnO and Sn(OH) 2 via a proposed reaction pathway and are further supported by X-ray photoemission spectroscopy (XPS). These nonperovskite Sn 2+ phases are beneficial because they assist in achieving the lower hole-doping levels in LT-VASP films. Remarkably, LT-VASP devices demonstrate improved air stability. Overall, our findings suggest that not only the commonly used SnF 2 but also other divalent Sn compounds could serve as Sn vacancy suppressors. Further work on modulating the perovskite film compositions could realize more efficient and stable tin-based perovskite solar cells. Σύνθεση και φασματοσκοπικός χαρακτηρισμός των ημιαγώγιμων, υβριδικών περοβσκίτων CH 3NH 3SnBr 3 και CH 3NH 3SnI 3 και των αρχικών αντιδραστηρίων CH 3NH 3Br, CH 3NH 3I και SnI 2. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια.. Συν-συγγραφή του άρθρου. 5 Στούμπος_Δημοσιεύσεις

6 6. W. Ke, C. C. Stoumpos, J. L. Logsdon, M. R. Wasielewski, Y. Yan, G. Fang, M. G. Kanatzidis, TiO 2- ZnS Cascade Electron Transport Layer for Efficient Formamidinium Tin Iodide Perovskite Solar Cells J. Am. Chem. Soc. 2016, 138, Achieving high open-circuit voltage (V oc) for tin-based perovskite solar cells is challenging. Here, we demonstrate that a ZnS interfacial layer can improve the Voc and photovoltaic performance of formamidinium tin iodide (FASnI 3) perovskite solar cells. The TiO 2 ZnS electron transporting layer (ETL) with cascade conduction band structure can effectively reduce the interfacial charge recombination and facilitate electron transfer. Our best-performing FASnI 3 perovskite solar cell using the cascaded TiO 2 ZnS ETL has achieved a power conversion efficiency of 5.27%, with a higher V oc of V, a short-circuit current density of ma cm 2, and a fill factor of 60.01%. The cascade structure is further validated with a TiO 2 CdS ETL. Our results suggest a new approach for further improving the performance of tin-based perovskite solar cells with a higher V oc. Σύνθεση και φασματοσκοπικός χαρακτηρισμός του ημιαγώγιμου, υβριδικού περοβσκίτη HC(NH 2) 2SnI 3 και των αρχικών αντιδραστηρίων HC(NH 2) 2I και SnI 2. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συν-συγγραφή του άρθρου. 6 Στούμπος_Δημοσιεύσεις

7 7. L. Ma; F. Hao; C. C. Stoumpos; B. T. Phelan; M. R. Wasielewski; M. G. Kanatzidis. "Carrier Diffusion Lengths of over 500 nm in Lead-Free Perovskite CH 3NH 3SnI 3 Films", J. Am. Chem. Soc. 2016, The dynamics of photoexcited lead-free perovskite films, CH 3NH 3SnI 3, were studied using broadband transient absorption and time-resolved fluorescence spectroscopy. Similar to its lead analogue CH 3NH 3PbI 3, we show that free carrier (electrons and holes) recombination is also the dominant relaxation pathway in CH 3NH 3SnI 3 films. The slow hot carrier relaxation time is 0.5 ps. Long carrier diffusion lengths for electrons (279 ± 88 nm) and holes (193 ± 46 nm) were obtained from fluorescence quenching measurements. We also show that SnF 2 doping in the CH 3NH 3SnI 3 film effectively increases the fluorescence lifetime up to 10 times and gives diffusion lengths exceeding 500 nm. These results suggest that the photophysics of CH 3NH 3SnI 3 perovskite are as favorable as those of CH 3NH 3PbI 3, demonstrating that it is a promising nontoxic lead-free replacement for lead iodide perovskite-based solar cells. Σύνθεση και φασματοσκοπικός χαρακτηρισμός του ημιαγώγιμου, υβριδικού περοβσκίτη CH 3NH 3SnI 3 και των αρχικών αντιδραστηρίων CH 3NH 3I και SnI 2. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια.. Συν-συγγραφή του άρθρου. 7 Στούμπος_Δημοσιεύσεις

8 8. O. Yaffe, Y. Guo, T. Hull, C. C. Stoumpos, L. Z. Tan, D. A. Egger, F. Zheng, G. Szpak, O. E. Semonin, A.N. Beecher, T. F. Heinz, L. Kronik, A. M. Rappe, M. G. Kanatzidis, J. S. Owen, M. A. Pimenta, L. E. Brus, Local polar fluctuations in lead halide perovskite crystals 2016, submitted to Phys. Rev. Lett. (arxiv: v2) *** Hybrid lead-halide perovskites have emerged as an excellent class of photovoltaic materials. Recent reports suggest that the organic molecular cation is responsible for local polar fluctuations that inhibit carrier recombination. We combine low frequency Raman scattering with first-principles molecular dynamics (MD) to study the fundamental nature of these local polar fluctuations. Our observations of a strong central peak in both hybrid (CH 3NH 3PbBr 3) and all-inorganic (CsPbBr 3) lead-halide perovskites show that anharmonic, local polar fluctuations are intrinsic to the general lead-halide perovskite structure, and not unique to the dipolar organic cation. MD simulations show that head-to-head Cs motion coupled to Br face expansion, on a few hundred femtosecond time scale, drives the local polar fluctuations in CsPbBr 3. Ανάπτυξη μονοκρυστάλλων του ημιαγώγιμου περοβσκίτη CsPbBr 3. Χαρακτηρισμός των οπτικών ιδιοτήτων. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε μονοκρυσταλλικά δείγματα. Συνσυγγραφή του άρθρου. ***Το άρθρο βρίσκεται υπό κρίση στο περιοδικό Phys. Rev. Lett. αλλά είναι διαθέσιμο στο διαδίκτυο σαν προ-δημοσιευμένο άρθρο στο σύνδεσμο: ( 8 Στούμπος_Δημοσιεύσεις

9 9. L. Mao, H. Tsai, W. Nie, L. Ma, J. Im, C. C. Stoumpos, C. D. Malliakas, F. Hao, M. R. Wasielewski, A. D. Mohite, M. G. Kanatzidis, Lead- and Tin-based Two-dimensional Hybrid Organic-inorganic Perovskites: Structure, Properties and Application in Planar Solar Cells Chem. Mater., 2016, 28, Hybrid halide perovskites are emerging semiconducting materials, with a diverse set of remarkable optoelectronic properties. Besides the widely studied three-dimensional (3D) perovskites, twodimensional (2D) perovskites show significant potential as photovoltaic (PV) active layers while exhibiting high moisture resistance. Here, we report two series of new 2D halide perovskite solid solutions: (HA)Pb 1 xsn xi 4 and (BZA) 2Pb 1 xsn xi 4 (x = 1, 0.75, 0.5, 0.25, 0), where HA stands for the organic spacer histammonium and BZA stands for benzylammonium cations. These compounds are assembled by cornersharing octahedral [MI 6] 4 units stabilizing singlelayered, anionic, inorganic perovskite sheets with organic cations filled in between. The optical band gaps are heavily affected by the M I M perovksite angles with the band gap steadily decreasing when the angle approaches 180, ranging from 2.18 ev for (BZA) 2PbI 4 to 2.05 ev for (HA)PbI 4. We find an anomalous trend in electronic band gap in the mixed compositions (HA)Pb 1 xsn xi 4 and (BZA) 2Pb 1 xsn xi 4. When Sn substitutes for Pb to form a solid solution, the band gap further decreases to 1.67 ev for (HA)SnI 4. The minimum band gap is at x = 0.75 at 1.74 ev. For BZA, the irregular trend is more intense, as all the intermediate compounds (BZA) 2Pb 1 xsn xi 4 (x = 0.75, 0.5, 0.25) have even slightly lower band gaps than (BZA) 2SnI 4 (1.89 ev). DFT calculations confirm the pure Pb and Sn compounds are direct band gap semiconductors. Relatively shorter photoluminescence (PL) lifetime in (BZA) 2PbI 4 than (HA)PbI 4 is observed, suggesting faster recombination rates of the carriers. Solution deposited thin films of (HA)PbI 4 and (BZA) 2PbI 4 show drastically different orientations with (HA)PbI4 displaying a perpendicular rather than parallel growth orientation with respect to the substrate, which is more favorable for PV devices. The higher potential in PV applications of the HA system is indicated by device performance, as the champion air stable planar device with the structure ITO/PEDOT:PSS/2D-perovskite/PCBM/Al of (HA)PbI 4 achieves a preliminary power conversion efficiency (PCE) of 1.13%, featuring an open-circuit voltage (V OC) of 0.91 V. Συνεπίβλεψη της διδακτορικής διατριβής της φοιτήτριας Lingling Mao. Συνδρομή σε όλα τα στάδια της σύνθεσης και του χαρακτηρισμού των ημιαγώγιμων, υβριδικών περοβσκιτικών στερεών διαλυμάτων HA)Pb 1 xsn xi 4 και (BZA) 2Pb 1 xsn xi 4 και της συγγραφής του άρθρου. 9 Στούμπος_Δημοσιεύσεις

10 10. S. M. Islam, C.D. Malliakas, D. Sarma, D. C. Maloney, C. C. Stoumpos, O. Y. Kontsevoi, A. J. Freeman, M. G. Kanatzidis, Direct Gap Semiconductors Pb 2BiS 2I 3, Sn 2BiS 2I 3 and Sn 2BiSI 5 Chem. Mater., 2016, 28, New quaternary thioiodides Pb 2BiS 2I 3, Sn 2BiS 2I 3, and Sn 2BiSI 5 have been synthesized by isothermal heating as well as chemical vapor transport. Pb 2BiS 2I 3 and Sn 2BiS 2I 3 crystallize in the space group, Cmcm, with unit cell parameters a = (9), b = (3), and c = (3) Å; a = (6), b = (2), and c = (3) Å, respectively. Sn 2BiSI 5 adopts a unique crystal structure that crystallizes in C2/m with cell parameters a = (3), b = (9), c = (4) Å, and β = 98.90(3). The crystal structures of Pb 2BiS 2I 3 and Sn 2BiS 2I 3 are strongly anisotropic and can be described as three-dimensional networks that are composed of parallel infinite ribbons of [M 4S 2I 4] (M = Pb, Sn, Bi) running along the crystallographic c-axis. The crystal structure of Sn 2BiSI 5 is a homologue of the M 2BiS 2I 3 (M = Pb, Sn) which has two successive ribbons of [M 4S 2I 4] separated by two interstitial (Sn 1 xbi xi 6) octahedral units. These compounds were characterized by scanning electron microscopy, differential thermal analysis, and X-ray photoelectron spectroscopy. Pb 2SbS 2I 3, Pb 2BiS 2I 3, Pb 2Sb 1 xbi xs 2I 3 (x 0.4), Sn 2BiS 2I 3 and Sn 2BiSI 5 are highly resistive and exhibit electrical resistivities of 3.0 GΩ cm, 100 MΩ cm, 65 MΩ cm, 1.2 MΩ cm, and 34 MΩ cm, respectively, at room temperature. Pb 2BiS 2I 3, Sn 2BiS 2I 3, Pb 2SbS 2I 3, Pb 2Sb 1 xbi xs 2I 3 (x 0.4), and Sn 2BiSI 5 are semiconductors with bandgaps of 1.60, 1.22, 1.92, 1.66, and 1.32 ev, respectively. The electronic band structures of Pb 2BiS 2I 3, Sn 2BiS 2I 3, and Sn 2BiSI 5, calculated using density functional theory, show that all compounds are direct bandgap semiconductors. Συνδρομή στην επίλυση και ανάλυση των κρυσταλλικών δομών των ενώσεων Pb 2BiS 2I 3, Sn 2BiS 2I 3 και Sn 2BiSI Στούμπος_Δημοσιεύσεις

11 11. X. Lü, Y. Wang, C. C. Stoumpos, Q. Hu, X. Guo, H. Chen, L. Yang, J. S. Smith, W. Yang, Y. Zhao, H. Xu, M. G. Kanatzidis, Q. Jia, Enhanced Structural Stability and Photo Responsiveness of CH 3NH 3SnI 3 Perovskite via Pressure-Induced Amorphization and Recrystallization Adv. Mater., 2016, 28, An organic inorganic halide CH 3NH 3SnI 3 perovskite with significantly improved structural stability is obtained via pressure-induced amorphization and recrystallization. In situ high-pressure resistance measurements reveal an increased electrical conductivity by 300% in the pressure-treated perovskite. Photocurrent measurements also reveal a substantial enhancement in visible-light responsiveness. The mechanism underlying the enhanced properties is shown to be associated with the pressure-induced structural modification. Σύνθεση και χαρακτηρισμός τoy ημιαγώγιμου, υβριδικού περοβσκίτη CH 3NH 3SnI 3. Ανάπτυξη πολυκρυσταλλικής σκόνης για περαιτέρω χαρακτηρισμό με περίθλαση ακτίνων-χ υπό υδροστατική πίεση. 11 Στούμπος_Δημοσιεύσεις

12 12. C. M. M. Soe, C. C. Stoumpos, B. Harutyunyan, E. F. Manley, L. X. Chen, M. J. Bedzyk, T. J. Marks, M. G. Kanatzidis, Room-Temperature Phase Transition in Methylammonium Lead Iodide Perovskite Thin Films Induced by Hydrohalic Acid Additives ChemSusChem, 2016, 9, Although reactive additives have been employed in perovskite solar cells to enhance film morphology and significantly increase device performance, little is known about the effect of these additives on perovskite structural and optical properties. Here we report a systematic study of how the properties of methylammonium lead iodide perovskite (CH 3NH 3PbI 3) are influenced by hydrohalic acid additives (HX; X=I, Br, Cl) in the precursor solution. Detailed structural and optical spectroscopic analysis reveals that all three acids affect the optical properties and alter the unit cell lattice parameters. Depending on the identity and concentration of HX, optical bandgaps widen or compress: addition of HBr yields a wider bandgap, whereas HI compresses the gap at high concentrations; HCl, on the other hand, has no significant effect on the bandgap. These changes can be understood by correlating them with the types of defects present in polycrystalline perovskite thin films in combination with the structural strain induced in very small crystallites. The presence of extra halides from HX in the precursor solution enables filling of the lattice vacancies in the perovskite, thereby altering metal halogen metal bond connectivity and consequently cell volumes and optical bandgaps. Remarkably, a room temperature tetragonal to cubic phase transition is observed for CH 3NH 3PbI 3 films treated with high HX concentrations. Further insights into this anomalous phase transformation are obtained from in situ variable-temperature X-ray diffraction in the o C ( K) range, revealing a monotonic fall in transition temperature with increasing precursor solution HX concentration. Σύνθεση και χαρακτηρισμός του ημιαγώγιμου, υβριδικού περοβσκίτη CH 3NH 3PbI 3. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συν-συγγραφή του άρθρου. 12 Στούμπος_Δημοσιεύσεις

13 13. D.H. Fabini, G. Laurita, J.S. Bechtel, C. C. Stoumpos, H. A. Evans, A. G. Kontos, Y. S. Raptis, P. Falaras, A. Van der Ven, M. G. Kanatzidis, R. Seshadri, Dynamic Stereochemical Activity of the Sn2+ Lone Pair in Perovskite CsSnBr 3 J. Am. Chem. Soc., 2016, 138, Stable s 2 lone pair electrons on heavy main-group elements in their lower oxidation states drive a range of important phenomena, such as the emergence of polar ground states in some ferroic materials. Here we study the perovskite halide CsSnBr 3 as an embodiment of the broader materials class. We show that lone pair stereochemical activity due to the Sn 2+ s 2 lone pair causes a crystallographically hidden, locally distorted state to appear upon warming, a phenomenon previously referred to as emphanisis. The synchrotron X-ray pair distribution function acquired between 300 and 420 K reveals emerging asymmetry in the nearest-neighbor Sn Br correlations, consistent with dynamic Sn 2+ off-centering, despite there being no evidence of any deviation from the average cubic structure. Computation based on density functional theory supports the finding of a lattice instability associated with dynamic offcentering of Sn 2+ in its coordination environment. Photoluminescence measurements reveal an unusual blueshift with increasing temperature, closely linked to the structural evolution. At low temperatures, the structures reflect the influence of octahedral rotation. A continuous transition from an orthorhombic structure (Pnma, no. 62) to a tetragonal structure (P4/mbm, no. 127) is found around 250 K, with a final, first-order transformation at 286 K to the cubic structure (Pm3 m, no. 221). Σύνθεση και χαρακτηρισμός τoy ημιαγώγιμου περοβσκίτη CsSnBr 3. Ανάπτυξη πολυκρυσταλλικής σκόνης για περαιτέρω χαρακτηρισμό με περίθλαση ακτίνων-χ και περίθλαση νετρονίων. Συλλογή δεδομένων με τη χρήση ακτινοβολίας σύγχροτρου συναρτήσει της θερμοκρασίας. Συν-συγγραφή του άρθρου. 13 Στούμπος_Δημοσιεύσεις

14 14. Y. Fu, H. Zhu, C. C. Stoumpos, Q. Ding, J. Wang, M. G. Kanatzidis, X. Zhu, S. Jin, Broad Wavelength Tunable Robust Lasing from Single-Crystal Nanowires of Cesium Lead Halide Perovskites (CsPbX 3, X = Cl, Br, I) ACS Nano, 2016, 10, Lead halide perovskite nanowires (NWs) are emerging as a class of inexpensive semiconductors with broad bandgap tunability for optoelectronics, such as tunable NW lasers. Despite exciting progress, the current organic inorganic hybrid perovskite NW lasers suffer from limited tunable wavelength range and poor material stability. Herein, we report facile solution growth of single-crystal NWs of inorganic perovskite CsPbX 3 (X = Br, Cl) and their alloys [CsPb(Br,Cl) 3] and a low temperature vapor-phase halide exchange method to convert CsPbBr 3 NWs into perovskite phase CsPb(Br,I) 3 alloys and metastable CsPbI 3 with wellpreserved perovskite crystal lattice and NW morphology. These single crystalline NWs with smooth end facets and subwavelength dimensions are ideal Fabry Perot cavities for NW lasers. Optically pumped tunable lasing across the entire visible spectrum ( nm) is demonstrated at room temperature from these NWs with low lasing thresholds and high-quality factors. Such highly efficient lasing similar to what can be achieved with organic inorganic hybrid perovskites indicates that organic cation is not essential for light emission application from these lead halide perovskite materials. Furthermore, the CsPbBr 3 NW lasers show stable lasing emission with no measurable degradation after at least 8 h or laser shots under continuous illumination, which are substantially more robust than their organic inorganic counterparts. The Cs-based perovskites offer a stable material platform for tunable NW lasers and other nanoscale optoelectronic devices. Σύνθεση και χαρακτηρισμός του ημιαγώγιμου, περοβσκίτη ενώσεων CsPbBr 3. Ανάπτυξη μονοκρυστάλλων με μικροσκοπικές διαστάσεις για περαιτέρω χαρακτηρισμό. Συν-συγγραφή του άρθρου. 14 Στούμπος_Δημοσιεύσεις

15 15. M. C. Gélvez-Rueda, D. H. Cao, S. Patwardhan, N. Renaud, C. C. Stoumpos, G. C. Schatz, J. T. Hupp, O. K. Farha, T. J. Savenije, M. G. Kanatzidis, F. C. Grozema, Effect of Cation Rotation on Charge Dynamics in Hybrid Halide Perovskites, J. Phys. Chem. C, 2016, 20, Organic inorganic hybrid halide perovskites are a promising class of materials for photovoltaic application with reported power efficiencies over 22%. However, not much is known about the influence of the organic dipole rotation and phase transitions on charge carrier dynamics. Here, we report substantial changes in mobility and lifetime of charge carriers in CH 3NH 3PbI 3 after the low-temperature tetragonal (β) to orthorhombic (γ) phase transition. By using microwave conductivity measurements, we observed that the mobility and lifetime of ionized charge carriers increase as the temperature decreases and a sudden increment is seen after the β γ phase transition. For CH 3NH 3PbI 3, the mobility and the halflifetime increase by a factor of 3 6 compared with the values before the β γ phase transition. We attribute the considerable change in the dynamics at low temperature to the decrease of the inherent dynamic disorder of the organic cation (CH 3NH 3+ ) inside the perovskite crystal structure. Σύνθεση και χαρακτηρισμός των ημιαγώγιμων, υβριδικών περοβσκιτικών ενώσεων CH 3NH 3PbBr 3 και CH 3NH 3PbΙ 3. Απομόνωση πολυκρυσταλλικής σκόνης για περαιτέρω χαρακτηρισμό. 15 Στούμπος_Δημοσιεύσεις

16 16. H. Tsai, W. Nie, J.-C. Blancon, C. C. Stoumpos, R. Asadpour, B. Harutyunyan, R. Verduzco, J. Crochet, S. Tretiak, L. Pedesseau, J. Even, M. A. Alam, G. Gupta, J. Lou, P.M. Ajayan, M. J. Bedzyk, M. G. Kanatzidis, A. D. Mohite, High-efficiency two-dimensional Ruddlesden-Popper perovskite solar cells Nature, 2016, 36, Three-dimensional organic inorganic perovskites have emerged as one of the most promising thin-film solar cell materials owing to their remarkable photophysical properties, which have led to power conversion efficiencies exceeding 20 per cent, with the prospect of further improvements towards the Shockley Queisser limit for a single junction solar cell (33.5 per cent). Besides efficiency, another critical factor for photovoltaics and other optoelectronic applications is environmental stability and photostability under operating conditions9 15. In contrast to their three-dimensional counterparts, Ruddlesden Popper phases layered two-dimensional perovskite films have shown promising stability, but poor efficiency at only 4.73 per cent. This relatively poor efficiency is attributed to the inhibition of out-ofplane charge transport by the organic cations, which act like insulating spacing layers between the conducting inorganic slabs. Here we overcome this issue in layered perovskites by producing thin films of near-single-crystalline quality, in which the crystallographic planes of the inorganic perovskite component have a strongly preferential out-of-plane alignment with respect to the contacts in planar solar cells to facilitate efficient charge transport. We report a photovoltaic efficiency of per cent with no hysteresis, and the devices exhibit greatly improved stability in comparison to their three-dimensional counterparts when subjected to light, humidity and heat stress tests. Unencapsulated two-dimensional perovskite devices retain over 60 per cent of their efficiency for over 2,250 hours under constant, standard (AM1.5G) illumination, and exhibit greater tolerance to 65 per cent relative humidity than do threedimensional equivalents. When the devices are encapsulated, the layered devices do not show any degradation under constant AM1.5G illumination or humidity. We anticipate that these results will lead to the growth of single-crystalline, solution-processed, layered, hybrid, perovskite thin films, which are essential for high-performance opto-electronic devices with technologically relevant long-term stability. Σύνθεση και χαρακτηρισμός των ημιαγώγιμων, δι-διάστατων (2D) υβριδικών περοβσκιτικών (CH 3(CH 2) 3NH 3) 2(CH 3NH 3) n 1Pb ni 3n+1. Χαρακτηρισμός οπτικών φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συν-συγγραφή του άρθρου. 16 Στούμπος_Δημοσιεύσεις

17 17. C. C. Stoumpos, M. G. Kanatzidis, Halide Perovskites: Poor Man s High Performance Semiconductors Adv. Mater., 2016, 28, Halide perovskites are a rapidly developing class of medium-bandgap semiconductors which, to date, have been popularized on account of their remarkable success in solid-state heterojunction solar cells raising the photovoltaic effi ciency to 20% within the last 5 years. As the physical properties of the materials are being explored, it is becoming apparent that the photovoltaic performance of the halide perovskites is just but one aspect of the wealth of opportunities that these compounds offer as highperformance semiconductors. From unique optical and electrical properties stemming from their characteristic electronic structure to highly efficient real-life technological applications, halide perovskites constitute a brand-new class of materials with exotic properties awaiting discovery. The nature of halide perovskites from the materials viewpoint is discussed here, enlisting the most important classes of the compounds and describing their most exciting properties. The topics covered focus on the optical and electrical properties highlighting some of the milestone achievements reported to date but also addressing controversies in the vastly expanding halide perovskite literature. Συγγραφή του άρθρου ανασκόπησης. Κριτική συζήτηση και σκέψεις πάνω στη χημεία και τη φυσική των περοβσκιτών που βασίζονται στα αλογονίδια. 17 Στούμπος_Δημοσιεύσεις

18 18. A. Kaltzoglou, M. Antoniadou, A. G. Kontos, C. C. Stoumpos, D. Perganti, E. Siranidi, V. Raptis, K. Trohidou, V. Psycharis, M. G. Kanatzidis, P. Falaras, Optical-Vibrational Properties of the Cs 2SnX 6 (X = Cl, Br, I) Defect Perovskites and Hole-Transport Efficiency in Dye-Sensitized Solar Cells, J. Phys. Chem. C, 2016, 120, We report the vibrational and optical properties of the defect perovskites Cs 2SnX 6 (X = Cl, Br, I) as well as their use as hole-transporting materials (HTMs) in solar cells. All three air-stable compounds were characterized using powder X-ray diffraction and Rietveld refinement. Far-IR reflectance, Raman, and UV vis spectroscopy as well as electronic band structure calculations show that the compounds are direct band gap semiconductors with a pronounced effect of the halogen atom on the size of the energy gap and the vibrational frequencies. Scanning electron microscopy and atomic force microscopy confirmed that the morphology of the perovskite films deposited from N,N -dimethylformamide solutions on TiO 2 substrates also strongly depends on the chemical composition of the materials. The Cs 2SnX 6 perovskites were introduced as hole-transporting materials in dye-sensitized solar cells, based on mesoporous titania electrodes sensitized with various organic and metal organic dyes. The solar cells based on Cs 2SnI 6 HTM and the Z907 dye performed best with a maximum power conversion efficiency of 4.23% at 1 sun illumination. The higher performance of Cs2SnI6 is attributed to efficient charge transport in the bulk material and hole extraction at the perovskite-pt interface, as evidenced by electrochemical impedance spectroscopy. Σύνθεση και φασματοσκοπικός χαρακτηρισμός του ημιαγώγιμου, ελαττωματικού περοβσκίτη Cs 2SnI 6. Συν-συγγραφή του άρθρου. 18 Στούμπος_Δημοσιεύσεις

19 19. F. Sun, L. Wang, C. C. Stoumpos, Synthesis, Structure, and Electronic Structure Calculation of a New Centrosymmetric Borate Pb 2O[BO 2(OH)] Based on Anion-centered OPb 4 Tetrahedra J. Sol. State Chem., 2016, 240, The synthesis, structure,and characterization of a new centrosymmetric borate Pb 2O[BO 2(OH)] based on anion-centered OPb 4 tetrahedra are reported.pb 2O[BO 2(OH)] crystallizes in monoclinic space group C2/m with a = (7)Å, b = 5.698(3) Å, c = 7.344(4)Å, β = (6). The electronic band structure and density of states of Pb 2O[BO 2(OH)] have been calculated via the density functional theory (DFT). Electron density difference calculation indicates thatl one-pair electrons of Pb 2+ cation should be stereoactive. Διαλογή μονοκρυστάλλων, συλλογή δεδομένων περίθλασης ακτίνων-χ και επίλυση της κρυσταλλικής δομής του βορικού άλατος Pb 2O[BO 2(OH)]. Συν-συγγραφή του άρθρου. 19 Στούμπος_Δημοσιεύσεις

20 20. C. C. Stoumpos, D. H. Cao, D. J. Clark, J. Young, J. M. Rondinelli, J. I. Jang, J. T. Hupp, M. G. Kanatzidis, Ruddlesden-Popper Hybrid Lead Iodide Perovskite 2D Homologous Semiconductors, Chem. Mater. 2016, 28, The hybrid two-dimensional (2D) halide perovskites have recently drawn significant interest because they can serve as excellent photoabsorbers in perovskite solar cells. Here we present the large scale synthesis, crystal structure, and optical characterization of the 2D (CH 3(CH 2) 3NH 3) 2(CH 3NH 3) n 1Pb ni 3n+1 (n = 1, 2, 3, 4, ) perovskites, a family of layered compounds with tunable semiconductor characteristics. These materials consist of well-defined inorganic perovskite layers intercalated with bulky butylammonium cations that act as spacers between these fragments, adopting the crystal structure of the Ruddlesden Popper type. We find that the perovskite thickness (n) can be synthetically controlled by adjusting the ratio between the spacer cation and the small organic cation, thus allowing the isolation of compounds in pure form and large scale. The orthorhombic crystal structures of (CH 3(CH 2) 3NH 3) 2(CH 3NH 3)Pb 2I 7 (n = 2, Cc2m; a = (4), b = (2) Å, c = (6)), (CH 3(CH 2) 3NH 3) 2(CH 3NH 3) 2Pb 3I 10 (n = 3, C2cb; a = (6), b = (4) Å, c = (6)), and (CH 3(CH 2) 3NH 3) 2(CH 3NH 3) 3Pb 4I 13 (n = 4, Cc2m; a = (4), b = (4) Å, c = (4)) have been solved by single-crystal X-ray diffraction and are reported here for the first time. The compounds are noncentrosymmetric, as supported by measurements of the nonlinear optical properties of the compounds and density functional theory (DFT) calculations. The band gaps of the series change progressively between 2.43 ev for the n = 1 member to 1.50 ev for the n = adopting intermediate values of 2.17 ev (n = 2), 2.03 ev (n = 3), and 1.91 ev (n = 4) for those between the two compositional extrema. DFT calculations confirm this experimental trend and predict a direct band gap for all the members of the Ruddlesden Popper series. The estimated effective masses have values of m h = 0.14 m 0 and m e = 0.08 m 0 for holes and electrons, respectively, and are found to be nearly composition independent. The band gaps of higher n members indicate that these compounds can be used as efficient light absorbers in solar cells, which offer better solution processability and good environmental stability. The compounds exhibit intense room-temperature photoluminescence with emission wavelengths consistent with their energy gaps, 2.35 ev (n = 1), 2.12 ev (n = 2), 2.01 ev (n = 3), and 1.90 ev (n = 4) and point to their potential use in light-emitting diodes. In addition, owing to the low dimensionality and the difference in dielectric properties between the organic spacers and the inorganic perovskite layers, these compounds are naturally occurring multiple quantum-well structures, which give rise to stable excitons at room temperature. Σύνθεση και χαρακτηρισμός των ημιαγώγιμων, δι-διάστατων υβριδικών περοβσκιτικών (CH 3(CH 2) 3NH 3) 2(CH 3NH 3) n 1Pb ni 3n+1 που ανήκουν στο δομικό τύπο που περιγράφτηκε για πρώτη φορά από τους Ruddlesden και Popper. Χαρακτηρισμός των οπτικών, φασματοσκοπικών ιδιοτήτων των υλικών. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε μονοκρυσταλλικά και πολυκρυσταλλικά δείγματα. Συλλογή κρυσταλλογραφικών δεδομένων και επίλυση κρυσταλλικής δομής. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συγγραφή του άρθρου. 20 Στούμπος_Δημοσιεύσεις

21 21. D. J. Clark, C. C. Stoumpos, F. O. Saouma, M. G. Kanatzidis, J. I. Jang, Polarization-selective Three-photon Absorption and Subsequent Photoluminescence in CsPbBr 3 Single Crystal at Room Temperature Phys. Rev. B, 2016, 93, We report on highly polarization-selective three-photon absorption (3PA) in a Bridgman-grown single crystal of CsPbBr 3 oriented along the (112) direction, which is an inorganic counterpart to emerging organic-inorganic hybrid halide perovskites for solar-cell and optoelectronic applications. The crystal exhibits strong photoluminescence (PL) at room temperature as a direct consequence of 3PA of fundamental radiation. Interestingly, 3PA disappears when the input polarization is parallel to the ( 110) direction. This 3PA effect is strongest when orthogonal to ( 110) and the corresponding 3PA coefficient was measured to be γ = 0.14 ± 0.03 cm 3 /GW 2 under picosecond-pulse excitation at the fundamental wavelength of λ = 1200 nm. The laser-induced damage threshold was also determined to be about 20 GW/cm 2 at the same wavelength. Based on relative PL intensities upon λ tuning over the entire 3PA range ( nm), we determined the nonlinear optical dispersion of the 3PA coefficient for CsPbBr 3, which is consistent with a theoretical prediction. Experimentally observed significant polarization dependence of γ was explained by relevant selection rules. The perovskite is potentially important for nonlinear optical applications owing to its highly efficient 3PA-induced PL response with a sharp on/off ratio by active polarization control. Ανάπτυξη μονοκρυστάλλων του ημιαγώγιμου περοβσκίτη CsPbBr 3. Χαρακτηρισμός των οπτικών ιδιοτήτων. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε μονοκρυσταλλικά δείγματα. Συνσυγγραφή του άρθρου. 21 Στούμπος_Δημοσιεύσεις

22 22. A. C. Wibowo, C. D. Malliakas, H. Li, C. C. Stoumpos, D. Y. Chung, B. W. Wessels, A. J. Freeman, M. G. Kanatzidis, An Unusual Crystal Growth Method of the Chalcohalide Semiconductor, β- Hg 3S 2Cl 2: a New Candidate for Hard Radiation Detection, Cryst. Growth Des. 2016, 16, We assess the mercury chalcohalide compound, β-hg 3S 2Cl 2, as a potential semiconductor material for X-ray and γ-ray detection. It has a high density (6.80 g/cm 3 ) and wide band gap (2.56 ev) and crystallizes in the cubic Pm3 n space group with a three-dimensional structure comprised of [Hg 12S 8] cubes with Cl atoms located within and between the cubes, featuring a trigonal pyramidal SHg 3 as the main building block. First-principle electronic structure calculations at the density functional theory level predict that the compound has closely lying indirect and direct band gaps. We have successfully grown transparent, single crystals of β-hg 3S 2Cl 2 up to 7 mm diameter and 1 cm long using a new approach by the partial decomposition of the quaternary Hg 3Bi 2S 2Cl 8 compound followed by the formation of β-hg 3S 2Cl 2 and an impermeable top layer, all happening in situ during vertical Bridgman growth. The decomposition process was optimized by varying peak temperatures and temperature gradients using a 2 mm/h translation rate of the Bridgman technique. Formation of the quaternary Hg 3Bi 2S 2Cl 8 followed by its partial decomposition into β-hg 3S 2Cl 2 was confirmed by in situ temperature-dependent synchrotron powder diffraction studies. The single crystal samples obtained had resistivity of Ω cm and mobilitylifetime products of electron and hole carriers of 1.4(4) 10 4 cm 2 /V and 7.5(3) 10 5 cm 2 /V, respectively. Further, an appreciable Ag X-ray photoconductivity response was observed showing the potential of β-hg 3S 2Cl 2 as a hard radiation detector material. στην ανάπτυξη μονοκρυστάλλων του χαλκο-αλογονιδίου β-hg 3S 2Cl Στούμπος_Δημοσιεύσεις

23 23. S. Tzani, K. N. Lazarou, C. C. Stoumpos, M. Pissas, V. Psycharis, Y. Sanakis, C. P. Raptopoulou, Iron(III) complexes with 2-pyridyl oxime ligands: Synthesis, structural and spectroscopic characterization, and magnetic studies, Chem. Select, 2016, 1, Reactions of Fe III sources with 2-pyridyl oxime ligands, pyc(r) NOH (R=H, Me, Ph), afforded the trinuclear oxo-centered complexes (NH 4)[Fe 3O(LH) 6(H 2O) 3](ClO 4) 8 MeOH 1.14H 2O (1 MeOH 1.14H 2O) and [Fe 3O{pyC(H)NO)(PhCO 2) 6(H 2O)] MeCN (2 MeCN), the tetranuclear complex [Fe 4(OH) 4{pyC(Me)NO} 4(H 2O) 4](ClO 4) 4 3Me 2CO H 2O (3 3Me 2CO H 2O), and the hexanuclear complexes [Fe 6(OH) 6{pyC(Me)NO} 6(H 2O) 6](ClO 4) 6 8Me 2CO 2H 2O (4 8Me 2CO 2H 2O), [Fe 6(OH) 6{pyC(Me)NO} 6(MeCONH 2) 6](ClO 4) 6 2MeCN H 2O (5 2MeCN H 2O), [Fe 6(OH) 6{pyC (Ph)NO} 6(H 2O) 6](ClO 4) 6 4.4Me 2CO 1.6Et 2O (6 4.4Me 2CO 1.6Et 2O) and [Fe 6(OH) 6{pyC(Ph)NO} 6(MeOH) 6](ClO 4) 5.5(OH) 0.5 MeOH 0.5H 2O (7 MeOH 0.5H 2O), where LH is the zwitterion anionic form of 2- pyridinecarboxylic acid (picolinic acid). Complex 3 can be described as inverse 12-metallacrown-4, whereas 4 7 can be described as inverse 18-metallacrowns-6 and represent the first examples of iron(iii) metallacyclic clusters with pyc(r)noh (R= H, Me, Ph) ligands. Complexes 3 and 6 were characterized by Mössbauer spectroscopy and magnetic susceptibility measurements, while complex 2 was characterized by EPR spectroscopy. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός της σύμπλοκης ένωσης [[Fe 6(OH) 6{pyC(Ph)NO} 6(MeOH) 6](ClO 4) 5.5(OH) 0.5 MeOH 0.5H 2O. 23 Στούμπος_Δημοσιεύσεις

24 24. T. Yokoyama, D. H. Cao, C. C. Stoumpos, T.-B. Song, Y. Sato, S. Aramaki, M. G. Kanatzidis, Overcoming Short-Circuit in Lead-Free CH 3NH 3SnI 3 Perovskite Solar Cells via Kinetically Controlled Gas Solid Reaction Film Fabrication Process, J. Phys. Chem. Lett., 2016, 7, The development of Sn-based perovskite solar cells has been challenging because devices often shoς shortcircuit behavior due to poor morphologies and undesired electrical properties of the thin films. A low-temperature vapor-assisted solution process (LT-VASP) has been employed as a novel kinetically controlled gas solid reaction film fabrication method to prepare leadfree CH3NH3SnI3 thin films. We show that the solid SnI2 substrate temperature is the key parameter in achieving perovskite films with high surface coverage and excellent uniformity. The resulting high quality CH 3NH 3SnI 3 films allow the successful fabrication of solar cells with drastically improved reproducibility, reaching an efficiency of 1.86%. Furthermore, our Kelvin probe studies show the VASP films have a doping level lower than that of films prepared from the conventional one-step method, effectively lowering the film conductivity. Above all, with (LT)-VASP, the short-circuit behavior often obtained from the conventional one step- fabricated Sn-based perovskite devices has been overcome. This study facilitates the path to more successful Sn-perovskite photovoltaic research. Σύνθεση και χαρακτηρισμός του ημιαγώγιμου, υβριδικού περοβσκίτη CH 3NH 3SnI 3 και των αρχικών αντιδραστηρίων CH 3NH 3I και SnI 2. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συν-συγγραφή του άρθρου. 24 Στούμπος_Δημοσιεύσεις

25 25. D. H. Fabini, T. Hogan, H. A. Evans, C. C. Stoumpos, M. G. Kanatzidis, R. Seshadri, Dielectric and Thermodynamic Signatures of Low-Temperature Glassy Dynamics in the Hybrid Perovskites CH 3NH 3PbI 3 and HC(NH 2) 2PbI 3, J. Phys. Chem. Lett., 2016, 7, Hybrid main group halide perovskites hold great technological promise in optoelectronic applications and present rich and complex evolution of structure and dynamics. Here we present low-temperature dielectric measurements and calorimetry of APbI 3 [A = CH 3NH 3+, HC(NH 2) 2+ ] that suggest glassy behavior on cooling. In both compounds, the dielectric loss displays frequency-dependent peaks below 100 K, characteristic of a glassy slowing of relaxation dynamics, with HC(NH 2) 2PbI 3 exhibiting greater glass fragility. Consistent with quenched disorder, the lowtemperature heat capacity of both perovskites deviates substantially from the T3 acoustic phonon contribution predicted by the Debye model. We suggest that static disorder of the A- site molecular cation, potentially coupled to local distortions of the Pb I sublattice, is responsible for these phenomena. The distinct low-temperature dynamics observed in these two perovskites suggest qualitative differences in the interaction between the molecular cation and the surrounding inorganic framework, with potential implications for defect screening and device performance at ambient temperatures. Σύνθεση και χαρακτηρισμός των ημιαγώγιμων, υβριδικών περοβσκιτικών ενώσεων CH 3NH 3PbΙ 3 και HC(NH 2) 2PbΙ 3. Ανάπτυξη μονοκρυστάλλων και πολυκρυσταλλικής σκόνης για περαιτέρω χαρακτηρισμό. Συν-συγγραφή του άρθρου. 25 Στούμπος_Δημοσιεύσεις

26 26. M. Sebastian, J. A. Peters, C. C. Stoumpos, J. Im, S. S. Kostina, Z. Liu, M. G. Kanatzidis, A. J. Freeman, B. W. Wessels, Excitonic Emissions and Above-Band-Gap Luminescence in the Single- Crystal Perovskite Semiconductors CsPbBr 3 and CsPbCl 3, Phys. Rev. B, 2015, 92, room-temperature radiation detection. The ternary compounds CsPbX 3 (X = Br or Cl) have perovskite structures that are being considered for optical and electronic applications such as lasing and gamma-ray detection. An above-band-gap excitonic photoluminescence (PL) band is seen in both CsPbX3 compounds. An excitonic emission peak centered at 2.98 ev, 0.1 ev above the room-temperature band gap, is observed for CsPbCl 3. The thermal quenching of the excitonic luminescence is well described by a two-step quenching model, yielding activation energies of and ev for high- and lowtemperature regimes, respectively. CsPbBr 3 exhibits bound excitonic luminescence peaks located at 2.29 and 2.33 ev that are attributed to recombination involving Br vacancy centers. Activation energies for thermal quenching of the excitonic luminescence of and ev were calculated for CsPbBr 3. Temperature-dependent PL experiments reveal unexpected blueshifts for all excitonic emission peaks in CsPbX 3 compounds. A phonon-assisted step-up process leads to the blueshift in CsPbBr 3 emission, while there is a contribution from band-gap widening in CsPbCl 3. The absence of significant deep level defect luminescence in these compounds makes them attractive candidates for high-resolution, Ανάπτυξη μονοκρυστάλλων των ημιαγώγιμων περοβσκιτικών ενώσεων CsPbCl 3 και CsPbBr 3. Χαρακτηρισμός των οπτικών ιδιοτήτων. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε μονοκρυσταλλικά και πολυκρυσταλλικά δείγματα. Συν-συγγραφή του άρθρου. 26 Στούμπος_Δημοσιεύσεις

27 27. F. Hao, C. C. Stoumpos, P. Guo, N. Zhou, T. J. Marks, R. P. H. Chang, M. G. Kanatzidis, Solvent- Mediated Crystallization of CH 3NH 3SnI 3 Films for Heterojunction Depleted Perovskite Solar Cells, J. Am. Chem. Soc., 2015, 137, Organo-lead halide perovskite solar cells have gained enormous significance and have now achieved power conversion efficiencies of 20%. However, the potential toxicity of lead in these systems raises environmental concerns for widespread deployment. Here we investigate solvent effects on the crystallization of the lead-free methylammonium tin triiodide (CH 3NH 3SnI 3) perovskite films in a solution growth process. Highly uniform, pinhole-free perovskite films are obtained from a dimethyl sulfoxide (DMSO) solution via a transitional SnI 2 3DMSO intermediate phase. This highquality perovskite film enables the realization of heterojunction depleted solar cells based on mesoporous TiO 2 layer but in the absence of any holetransporting material with an unprecedented photocurrent up to 21 ma. cm 2. Charge extraction and transient photovoltage decay measurements reveal high carrier densities in the CH 3NH 3SnI 3 perovskite device which are one order of magnitude larger than CH 3NH 3PbI 3-based devices but with comparable recombination lifetimes in both devices. The relatively high background dark carrier density of the Snbased perovskite is responsible for the lower photovoltaic efficiency in comparison to the Pb-based analogues. These results provide important progress toward achieving improved perovskite morphology control in realizing solution processed highly efficient lead-free perovskite solar cells. Σύνθεση και χαρακτηρισμός του ημιαγώγου CH 3NH 3SnI 3. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια.. Διαλογή μονοκρυστάλλων, συλλογή δεδομένων περίθλασης ακτίνων-χ και επίλυση της κρυσταλλικής δομής SnI 2 3DMSO ως ενδιάμεσο παράγωγο στο σχηματισμό του περοβσκίτη. Συνσυγγραφή του άρθρου. 27 Στούμπος_Δημοσιεύσεις

28 28. J. Im, C. C. Stoumpos, H. Jin, A. J. Freeman, M. G. Kanatzidis, Antagonism Between Spin-Orbit Coupling and Steric Effects Causes Anomalous Bandgap Suppression in the Perovskite Materials CH 3NH 3Sn 1-xPb xi 3, J. Phys. Chem. Lett., 2015, 6, Halide perovskite solar cells are a recent ground-breaking development achieving power conversion efficiencies exceeding 18%. This has become possible owing to the remarkable properties of the AMX 3 perovskites, which exhibit unique semiconducting properties. The most efficient solar cells utilize the CH 3NH 3PbI 3 perovskite whose band gap, E g, is 1.55 ev. Even higher efficiencies are anticipated, however, if the band gap of the perovskite can be pushed deeper in the near-infrared region, as in the case of CH 3NH 3SnI 3 (E g = 1.3 ev). A remarkable way to improve further comes from the CH 3NH 3Sn 1 xpb xi 3 solid solution, which displays an anomalous trend in the evolution of the band gap with the compositions approaching x = 0.5 displaying lower band gaps (E g 1.1 ev) than that of the lowest of the end member, CH 3NH 3SnI 3. Here we use first principles calculations to show that the competition between the spin orbit coupling (SOC) and the lattice distortion is responsible for the anomalous behavior of the band gap in CH 3NH 3Sn 1 xpb xi 3. SOC causes a linear reduction as x increases, while the lattice distortion causes a nonlinear increase due to a composition-induced phase transition near x = 0.5. Our results suggest that electronic structure engineering can have a crucial role in optimizing the photovoltaic performance. Σύνθεση και χαρακτηρισμός του ημιαγώγιμου, υβριδικού περοβσκιτικού στερεού διαλύματος CH 3NH 3Sn 1 xpb xi 3. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε μονοκρυστάλλους και προσδιορισμός του ενεργειακού χάσματος, ως αρχικές συνθήκες για τους θεωρητικούς υπολογισμούς. Συν-συγγραφή του άρθρου. 28 Στούμπος_Δημοσιεύσεις

29 29. C. C. Stoumpos, M. G. Kanatzidis, The Renaissance of Halide Perovskites and their Evolution as Emerging Optoelectronic Materials, Acc. Chem. Res., 2015, 48, The recent re-emergence of the halide perovskites, of the type AMX 3, derives from a sea-changing breakthrough in the field of photovoltaics that has led to a whole new generation of solar devices with remarkable power conversion efficiency. The success in the field of photovoltaics has led to intense, combined research efforts to better understand these materials both from the fundamental chemistry and physics points of view and for the improvement of applied functional device engineering. This groundswell of activity has breathed new life into this long-known but largely forgotten class of perovskites. The impressive achievements of halide perovskites in photovoltaics, as well as other optoelectronic applications, stem from an unusually favorable combination of optical and electronic properties, with the ability to be solution processed into films. This defines them as a brand-new class of semiconductors that can rival or exceed the performance of the venerable classes of III V and II IV semiconductors, which presently dominate the industries of applied optoelectronics. Our aim in this Account is to highlight the basic pillars that define the chemistry of the halide perovskites and their unconventional electronic properties through the prism of structure property relationships. We focus on the synthetic requirements under which a halide perovskite can exist and emphasize how the synthetic conditions can determine the structural integrity and the bulk properties of the perovskites. Then we proceed to discuss the origins of the optical and electronic phenomena, using the perovskite crystal structure as a guide. Some of the most remarkable features of the perovskites dealt with in this Account include the evolution of a unique type of defect, which gives rise to superlattices. These can enhance or diminish the fluorescence properties of the perovskites. For example, the exotic self-doping ability of the Sn-based perovskites allows them to adopt electrical properties from semiconducting to metallic. We attempt to rationalize how these properties can be tuned and partially controlled through targeted synthetic procedures for use in electronic and optical devices. In addition, we address open scientific questions that pose big obstacles in understanding the fundamentals of perovskites. We anticipate that the answers to these questions will provide the impetus upon which future research directions will be founded. Συγγραφή του άρθρου ανασκόπησης. Συμμετοχή στα περισσότερα από τα επιστημονικά αποτελέσματα που παρουσιάζονται στο άρθρο. 29 Στούμπος_Δημοσιεύσεις

30 30. F. Han, X. Wan, D. Phelan, C. C. Stoumpos, M. Sturza, C. D. Malliakas, Q. a. Li, T.-H. Han, Q. Zhao, D. Y. Chung, M. G. Kanatzidis, Antiferromagnetic Kondo Lattice in the Layered Compound CePd 1-xBi2 and Comparison to the Superconductor LaPd 1-xBi 2, Phys. Rev. B 2015, 92, The layered compound CePd 1 xbi 2 with the tetragonal ZrCuSi 2-type structure was obtained from excess Bi flux. Magnetic susceptibility data of CePd 1 xbi 2 show an antiferromagnetic ordering below 6 K and are anisotropic along the c axis and the ab plane. The anisotropy is attributed to crystal-electric-field (CEF) effects and a CEF model which is able to describe the susceptibility data is given. An enhanced Sommerfeld coefficient γ of J mol Ce 1 K 2 obtained from specific-heat measurement suggests a moderate Kondo effect in CePd 1 xbi 2. Other than the antiferromagnetic peak at 6 K, the resistivity curve shows a shoulder-like behavior around 75 K which could be attributed to the interplay between Kondo and CEF effects. Magnetoresistance and Hall-effect measurements suggest that the interplay reconstructs the Fermi-surface topology of CePd 1 xbi 2 around 75 K. Electronic structure calculations reveal that the Pd vacancies are important to the magnetic structure and enhance the CEF effects which quench the orbital moment of Ce at low temperatures. Διαλογή μονοκρυστάλλων, συλλογή δεδομένων περίθλασης ακτίνων-χ και επίλυση της κρυσταλλικής δομής των διαμεταλλικών ενώσεων LaPd 1 xbi 2 και CePd 1 xbi Στούμπος_Δημοσιεύσεις

31 31. D. A. Valverde-Chávez, C. Ponseca Jr., C. C. Stoumpos, A. Yartsev, M. G. Kanatzidis, V. Sundström, D. G. Cooke, Intrinsic Femtosecond Charge Generation Dynamics in Single Crystal CH 3NH 3PbI 3, Energy Environ. Sci., 2015, 8, Hybrid metal organic perovskite solar cells have astounded the solar cell community with their rapid rise in efficiency while maintaining low-cost fabrication. The intrinsic material photophysics related to the generation of free charges, their dynamics and efficiency, however, remains to be understood. As fabrication techniques improve, larger crystal grain sizes have been shown to be a critical factor for improving both the optical and transport properties of the hybrid metal halide perovskites. In this work, we use pulses of multi-thz frequency light in the ultra-broadband 1 30 THz (4 125 mev) range to observe the ac conductivity in large single crystal CH 3NH 3PbI 3. Our spectra reveal the ultrafast dynamics and efficiencies of free charge creation and extremely high charge carrier mobility as high as cm 2 V -1 s -1. While quasi-equilibrium analysis of efficiencies through the Saha equation suggests a binding energy on the order of 49 mev, an observed reflectance feature appearing at high pump fluence occurs at 12 mev and is consistent with an orbital transition of the exciton, indicating a much lower Rydberg energy of 17 mev at room temperature. The signature of the exciton is found to vanish on a 1 ps time scale commensurate with the appearance of mobile carriers, consistent with thermal dissociation of the exciton to the continuum in the room temperature tetragonal phase. Ανάπτυξη μονοκρυστάλλων του ημιαγώγου CH 3NH 3PbI 3. Συν-συγγραφή του άρθρου. 31 Στούμπος_Δημοσιεύσεις

32 32. D. A. Valverde-Chávez, C. Ponseca Jr., C. C. Stoumpos, A. Yartsev, M. G. Kanatzidis, V. Sundström, D. G. Cooke, Optical Pump - Multi-THz Probe Spectroscopy of a Single Crystal Organic Hybrid Lead Halide Perovskite CLEO JW2A.50. We analyzed ultrafast photocarrier generation in single crystal CH 3NH 3PbI 3 perovskite through timeresolved terahertz spectroscopy. We find a Drude-Lorentz type conductivity spectra with a carrier mobility of 35 cm 2 /Vs and a Lorentzian component at 45 mev possibly due to intraexcitonic transitions. Ανάπτυξη μονοκρυστάλλων του ημιαγώγου CH 3NH 3PbI Στούμπος_Δημοσιεύσεις

33 33. Q. Zhao, F. Han, C. C. Stoumpos, T.-H. Han, H. Li, J. F. Mitchell, New Insulating Antiferromagnetic Quaternary Iridates MLa 10Ir 4O 24 (M = Sr, Ba), Sci. Rep. 2015, 5, Recently, oxides of Ir4+ have received renewed attention in the condensed matter physics community, as it has been reported that certain iridates have a strongly spin-orbital coupled (SOC) electronic state, J eff = ½, that defines the electronic and magnetic properties. The canonical example is the Ruddlesden-Popper compound Sr2IrO4, which has been suggested as a potential route to a new class of high temperature superconductor due to the formal analogy between J eff = ½ and the S = ½ state of the cuprate superconductors. The quest for other iridium oxides that present tests of the underlying SOC physics is underway. In this spirit, here we report the synthesis and physical properties of two new quaternary tetravalent iridates, MLa 10Ir 4O 24 (M = Sr, Ba). The crystal structure of both compounds features isolated IrO 6 octahedra in which the electronic configuration of Ir is d 5. Both compounds order antiferromagnetically despite the lack of obvious superexchange pathways, and resistivity measurement shows that SrLa 10Ir 4O 24 is an insulator. Διαλογή μονοκρυστάλλων, συλλογή δεδομένων περίθλασης ακτίνων-χ και επίλυση της κρυσταλλικής δομής των οξειδίων SrLa 10Ir 4O 24 και BaLa 10Ir 4O Στούμπος_Δημοσιεύσεις

34 34. D. H. Cao, C. C. Stoumpos, O. K. Farha, J. T. Hupp. M. G. Kanatzidis, 2D Homologous Perovskites as Light Absorbing Materials for Solar Cell Applications, J. Am. Chem. Soc., 2015, 137, We report on the fabrication and properties of the semiconducting 2D (CH 3(CH 2) 3NH 3) 2(CH 3NH 3) n 1Pb ni 3n+1 (n = 1, 2, 3, and 4) perovskite thin films. The band gaps of the series decrease with increasing n values, from 2.24 ev (CH 3(CH 2) 3NH 3) 2PbI 4 (n = 1) to 1.52 ev CH 3NH 3PbI 3 (n = ). The compounds exhibit strong light absorption in the visible region, accompanied by strong photoluminescence at room temperature, rendering them promising light absorbers for photovoltaic applications. Moreover, we find that thin films of the semi-2d perovskites display an ultrahigh surface coverage as a result of the unusual film selfassembly that orients the [Pb ni 3n+1] layers perpendicular to the substrates. We have successfully implemented this 2D perovskite family in solid-state solar cells, and obtained an initial power conversion efficiency of 4.02%, featuring an opencircuit voltage (Voc) of 929 mv and a short-circuit current density (Jsc) of 9.42 ma/cm 2 from the n = 3 compound. This result is even more encouraging considering that the device retains its performance after long exposure to a high-humidity environment. Overall, the homologous 2D halide perovskites define a promising class of stable and efficient light-absorbing materials for solid-state photovoltaics and other applications. Σύνθεση και χαρακτηρισμός των ημιαγώγιμων, δι-διάστατων (2D) υβριδικών περοβσκιτών CH 3(CH 2) 3NH 3) 2(CH 3NH 3) n 1Pb ni 3n+1. Χαρακτηρισμός των οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συν-συγγραφή του άρθρου. 34 Στούμπος_Δημοσιεύσεις

35 35. D. Koumoulis, T. C. Chasapis, B. Leung, R.E. Taylor, C. C. Stoumpos, N. P. Calta, M. G. Kanatzidis, L. S. Bouchard, Site-Specific Contributions to the Band Inversion in a Topological Crystalline Insulator, Adv. El. Mater. 2015, 1, In a topological crystalline insulator (TCI) the inversion of the bulk valence and conduction bands is a necessary condition to observe surface metallic states. Solid solutions of Pb 1- xsn xte have been shown to be TCI, where band inversion occurs as a result of the band gap evolution upon alloying with Sn. The origins of this band inversion remain unclear. Herein the role of Sn insertion into the PbTe matrix is investigated for the p-type Pb 1-xSn xte series with x = 0, 0.35, 0.60, and 1.00 via nuclear magnetic resonance (NMR) and transport measurements. 207 Pb, 119 Sn, and 125 Te line shapes, spin-lattice relaxation rates, and Knight shifts provide site-specific characterization of the electronic band structure. This probe of the electronic band structure shows that the band inversion is unaffected by lattice distortions but related to spatial electronic inhomogeneities formed by Sn incorporation into the PbTe matrix. Strong relativistic effects are found to be responsible for the band inversion, regardless of carrier type and concentration, suggesting a novel interpretation of the band gap evolution with composition. The temperature dependences of the NMR parameters reveal a negative temperature coefficient of the direct gap for SnTe and positive coefficient for PbTe. Ανάπτυξη μονοκρυστάλλων του ημιαγώγιμου στερεού διαλύματος Pb 1-xSn xte. Χαρακτηρισμός των μονοκρυστάλλων με κρυσταλλογραφία Laue. 35 Στούμπος_Δημοσιεύσεις

36 36. C. C. Stoumpos, L. Fraser, D. J. Clark, Y. S. Kim, S. H. Rhim, A. J. Freeman, J. B. Ketterson, J. I. Jang, M. G. Kanatzidis, Hybrid Germanium Iodide Perovskite Semiconductors: Active Lone Pairs, Structural Distortions, Direct and Indirect Energy Gaps and Strong Nonlinear Optical Properties, J. Am. Chem. Soc., 2015, 137, The synthesis and properties of the hybrid organic/inorganic germanium perovskite compounds, AGeI 3, are reported (A = Cs, organic cation). The systematic study of this reaction system led to the isolation of 6 new hybrid semiconductors. Using CsGeI 3 (1) as the prototype compound, we have prepared methylammonium, CH 3NH 3GeI 3 (2), formamidinium, HC(NH 2) 2GeI 3 (3), acetamidinium, CH 3C(NH 2) 2GeI 3 (4), guanidinium, C(NH2) 3GeI 3 (5), trimethylammonium, (CH 3) 3NHGeI 3 (6), and isopropylammonium, (CH 3) 2C(H)NH 3GeI 3 (7) analogues. The crystal structures of the compounds are classified based on their dimensionality with 1 4 forming 3D perovskite frameworks and 5 7 1D infinite chains. Compounds 1 7, with the exception of compounds 5 (centrosymmetric) and 7 (nonpolar acentric), crystallize in polar space groups. The 3D compounds have direct band gaps of 1.6 ev (1), 1.9 ev (2), 2.2 ev (3), and 2.5 ev (4), while the 1D compounds have indirect band gaps of 2.7 ev (5), 2.5 ev (6), and 2.8 ev (7). Herein, we report on the second harmonic generation (SHG) properties of the compounds, which display remarkably strong, type I phase-matchable SHG response with high laser-induced damage thresholds (up to 3 GW/cm 2 ). (2) The second-order nonlinear susceptibility, χ S, was determined to be ± 10.5 pm/v (1), (161.0 ± 14.5) pm/v (2), ± 13.5 pm/v (3), and 57.2 ± 5.5 pm/v (4). First-principles density functional theory electronic structure calculations indicate that the large SHG response is attributed to the high density of states in the valence band due to sp-hybridization of the Ge and I orbitals, a consequence of the lone pair activation. Σύνθεση και χαρακτηρισμός των ημιαγώγιμων, υβριδικών περοβσκιτικών ενώσεων του γερμανίου CsGeΙ 3, CH 3NH 3GeΙ 3, HC(NH 2) 2GeΙ 3, CH 3C(NH 2) 2GeΙ 3, C(NH 2) 3GeI 3, (CH 3) 3NHGeI 3 και (CH 3) 2C(H)NH 3GeI 3. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε μονοκρυσταλλικά και πολυκρυσταλλικά δείγματα. Συλλογή κρυσταλλογραφικών δεδομένων και επίλυση κρυσταλλικής δομής. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συγγραφή του άρθρου. 36 Στούμπος_Δημοσιεύσεις

37 37. S.-H. Chun, J.-W. Kim, J. Kim, H. Zheng, C. C. Stoumpos, C. D. Malliakas, J. F. Mitchell, K. Mehlawat, Y. Singh, Y. Choi, T. Gog, A. Al-Zein, M. Moretti Sala, M. Krisch, J. Chaloupka, G. Jackeli, G. Khaliullin, B. J. Kim, Direct Evidence for Dominant Bond-directional Interactions in a Honeycomb Lattice Iridate Na 2IrO 3, Nat. Phys. 2015, 11, Heisenberg interactions are ubiquitous in magnetic materials and play a central role in modelling and designing quantum magnets. Bond-directional interactions offer a novel alternative to Heisenberg exchange and provide the building blocks of the Kitaev model4, which has a quantum spin liquid as its exact ground state. Honeycomb iridates, A 2IrO 3 (A = Na, Li), offer potential realizations of the Kitaev magnetic exchange coupling, and their reported magnetic behavior may be interpreted within the Kitaev framework. However, the extent of their relevance to the Kitaev model remains unclear, as evidence for bonddirectional interactions has so far been indirect. Here, we present direct evidence for dominant bonddirectional interactions in antiferromagnetic Na 2IrO 3 and show that they lead to strong magnetic frustration. Diffuse magnetic X-ray scattering reveals broken spin-rotational symmetry even above the Néel temperature, with the three spin components exhibiting short-range correlations along distinct crystallographic directions. This spin- and real-space entanglement directly uncovers the bonddirectional nature of these interactions, thus providing a direct connection between honeycomb iridates and Kitaev physics. Διαλογή μονοκρυστάλλων, συλλογή δεδομένων περίθλασης ακτίνων-χ και επίλυση της κρυσταλλικής δομής του οξειδίου Na 2IrO Στούμπος_Δημοσιεύσεις

38 38. S. M. Islam, S. Vanishri, H. Li, C. C. Stoumpos, J. A. Peters, M. Sebastian, Z. Liu, S. Wang, A. S. Haynes, J. Im, A. J. Freeman, B. W. Wessels, M. G. Kanatzidis, Cs 2Hg 3S 4: A Low-Dimensional Direct Bandgap Semiconductor, Chem. Mater., 2015, 27, Cs 2Hg 3S 4 was synthesized by slowly cooling a melted stoichiometric mixture of Hg and Cs 2S 4. Cs 2Hg 3S 4 crystallizes in the Ibam spacegroup with a = 6.278(1) Å, b = (2) Å, and c = (3)Å; d calc = 6.29 g/cm 3. Its crystal structure consists of straight chains of [Hg 3S 4] n 2n that engage in side-by-side weak bonding interactions forming layers and are charge balanced by Cs+ cations. The thermal stability of this compound was investigated with differential thermal analysis and temperature dependent in situ synchrotron powder diffraction. The thermal expansion coefficients of the a, b, and c axes were assessed at , , and K 1, respectively. Large single-crystals up to 5 cm in length and 1 cm in diameter were grown using a vertical Bridgman method. Electrical conductivity and photoconductivity measurements on naturally cleaved crystals of Cs 2Hg 3S 4 gave resistivity ρ of 10 8 Ω cm and carrier mobility-lifetime (μτ) products of and cm 2 V 1 for electrons and holes, respectively. Cs 2Hg 3S 4 is a semiconductor with a bandgap Eg 2.8 ev and exhibits photoluminescence (PL) at low temperature. Electronic band structure calculations within the density functional theory (DFT) framework employing the nonlocal hybrid functional within Heyd Scuseria Ernzerhof (HSE) formalism indicate a direct bandgap of 2.81 ev at Γ. The theoretical calculations show that the conduction band minimum has a highly dispersive and relatively isotropic mercury-based s-orbital-like character while the valence band maximum features a muchless dispersive and more anisotropic sulfur orbital-based band. Συλλογή και ανάλυση δεδομένων περίθλασης ακτίνων-χ πολυκρυσταλλικής σκόνης της ένωσης Cs 2Hg 3S 4 με τη χρήση ακτινοβολίας σύγχροτρου για τον προσδιορισμό του συντελεστή θερμικής διαστολής. 38 Στούμπος_Δημοσιεύσεις

39 39. L. Fang, J. Im, C. C. Stoumpos, F. Shi, V. Dravid, M. Leroux, A. J. Freeman, W.-K. Kwok, D. Y. Chung, M. Kanatzidis, Two-Dimensional Mineral [Pb 2BiS 3][AuTe 2]: High-Mobility Charge Carriers in Single-Atom-Thick Layers J. Am. Chem. Soc., 2015, 137, Two-dimensional (2D) electronic systems are of wide interest due to their richness in chemical and physical phenomena and potential for technological applications. Here we report that [Pb 2BiS 3][AuTe 2], known as the naturally occurring mineral buckhornite, hosts 2D carriers in single-atom thick layers. The structure is composed of stacking layers of weakly coupled [Pb 2BiS 3] and [AuTe 2] sheets. The insulating [Pb 2BiS 3] sheet inhibits interlayer charge hopping and confines the carriers in the basal plane of the single-atom-thick [AuTe 2] layer. Magneto-transport measurements on synthesized samples and theoretical calculations show that [Pb 2BiS 3][AuTe 2] is a multiband semimetal with a compensated density of electrons and holes, which exhibits a high hole carrier mobility of 1360 cm 2 /(Vs). This material possesses an extremely large anisotropy, Γ = ρc/ρab 104, comparable to those of the benchmark 2D materials graphite and Bi 2Sr 2CaCu 2O 6+δ. The electronic structure features linear band dispersion at the Fermi level and ultrahigh Fermi velocities of 106 m/s, which are virtually identical to those of graphene. The weak interlayer coupling gives rise to the highly cleavable property of the single crystal specimens. Our results provide a novel candidate for a monolayer platform to investigate emerging electronic properties. Διαλογή μονοκρυστάλλων, συλλογή δεδομένων περίθλασης ακτίνων-χ και επίλυση της κρυσταλλικής δομής του συνθετικού ορυκτού μπακχορνίτη [Pb 2BiS 3][AuTe 2]. 39 Στούμπος_Δημοσιεύσεις

40 40. F. Hao, C. C. Stoumpos, Z. Liu, R. P. H. Chang, and M. G. Kanatzidis, Controllable Perovskite Crystallization at a Gas Solid Interface for Hole Conductor-Free Solar Cells with Steady Power Conversion Efficiency over 10% J. Am. Chem. Soc., 2014, 136, Depositing a pinhole-free perovskite film is of paramount importance to achieve high performance perovskite solar cells, especially in a heterojunction device format that is free of hole transport material (HTM). Here, we report that high-quality pinhole-free CH 3NH 3PbI 3 perovskite film can be controllably deposited via a facile low-temperature (<150 C) gas solid crystallization process. The crystallite formation process was compared with respect to the conventional solution approach, in which the needle-shaped solvation intermediates (CH 3NH 3PbI 3 DMF and CH 3NH 3PbI 3 H 2O) have been recognized as the main cause for the incomplete coverage of the resultant film. By avoiding these intermediates, the films crystallized at the gas solid interface offer several beneficial features for device performance including high surface coverage, small surface roughness, as well as controllable grain size. Highly efficient HTM-free perovskite solar cells were constructed with these pinhole-free CH 3NH 3PbI 3 films, exhibiting significant enhancement of the light harvesting in the long wavelength regime with respect to the conventional solution processed one. Overall, the gas solid method yields devices with an impressive power conversion efficiency of 10.6% with high reproducibility displaying a negligible deviation of 0.1% for a total of 30 cells. Σύνθεση και χαρακτηρισμός του ημιαγώγιμου, υβριδικού περοβσκίτη CH 3NH 3PbI 3. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Διαλογή μονοκρυστάλλων, συλλογή δεδομένων περίθλασης ακτίνων-χ και επίλυση των κρυσταλλικών δομών των επιδιαλυτωμένων περοβσκιτών CH 3NH 3PbI 3 DMF και CH 3NH 3PbI 3 H 2O Συν-συγγραφή του άρθρου. 40 Στούμπος_Δημοσιεύσεις

41 41. B. Lee, C. C. Stoumpos, N. Zhou, F. Hao, C. D. Malliakas, C.-Y. Yeh, T. J. Marks, M. G. Kanatzidis, R. P. H. Chang, Air-Stable Molecular Semiconducting Iodosalts for Solar Cell Applications: Cs2SnI6 as a Hole Conductor, J. Am. Chem. Soc., 2014, 136, We introduce a new class of molecular iodosalt compounds for application in nextgeneration solar cells. Unlike tin based perovskite compounds CsSnI 3 and CH 3NH 3SnI 3, which have Sn in the 2+ oxidation state and must be handled in an inert atmosphere when fabricating solar cells, the Sn in the molecular iodosalt compounds is in the 4+ oxidation state, making them stable in air and moisture. As an example, we demonstrate that, using Cs 2SnI 6 as a hole transporter, we can successfully fabricate in air a solid-state dye-sensitized solar cell (DSSC) with a mesoporous TiO 2 film. Doping Cs 2SnI 6 with additives helps to reduce the internal device resistance, improving cell efficiency. In this way, a Z907 DSSC delivers 4.7% of energy conversion efficiency. By using a more efficient mixture of porphyrin dyes, an efficiency near 8% with photon confinement has been achieved. This represents a significant step toward the realization of low-cost, stable, lead-free, and environmentally benign next-generation solid-state solar cells. Σύνθεση και χαρακτηρισμός του ημιαγώγιμου, ελαττωματικού περοβσκίτη Cs 2SnI 6. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συν-συγγραφή του άρθρου. 41 Στούμπος_Δημοσιεύσεις

42 42. D. H. Cao, C. C. Stoumpos, C. D. Malliakas, M. J. Katz, O. K. Farha, J. T. Hupp, M. G. Kanatzidis, Remnant PbI 2, an Unforeseen Necessity in High-Efficiency Hybrid Perovskite-Based Solar Cells?, APL Materials, 2014, 2, Perovskite-containing solar cells were fabricated in a two-step procedure in which PbI 2 is deposited via spin-coating and subsequently converted to the CH 3NH 3PbI 3 perovskite by dipping in a solution of CH 3NH 3I. By varying the dipping time from 5 s to 2 h, we observe that the device performance shows an unexpectedly remarkable trend. At dipping times below 15 min the current density and voltage of the device are enhanced from 10.1 ma/cm 2 and 933 mv (5 s) to 15.1 ma/cm 2 and 1036 mv (15 min). However, upon further conversion, the current density decreases to 9.7 ma/cm 2 and 846 mv after 2 h. Based on X-ray diffraction data, we determined that remnant PbI 2 is always present in these devices. Work function and dark current measurements showed that the remnant PbI 2 has a beneficial effect and acts as a blocking layer between the TiO 2 semiconductor and the perovskite itself reducing the probability of back electron transfer (charge recombination). Furthermore, we find that increased dipping time leads to an increase in the size of perovskite crystals at the perovskite-hole-transporting material interface. Overall, approximately15 min dipping time ( 2% unconverted PbI 2) is necessary for achieving optimal device efficiency. Σύνθεση και χαρακτηρισμός του ημιαγώγιμου, υβριδικού περοβσκίτη CH 3NH 3PbI 3 και των αρχικών αντιδραστηρίων CH 3NH 3I και PbI 2. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συν-συγγραφή του άρθρου. 42 Στούμπος_Δημοσιεύσεις

43 43. L. Fang, C. C. Stoumpos, Y. Jia, A. Glatz, D.-Y. Chung, H. Claus, U. Welp, W. K. Kwok, M. G. Kanatzidis, Dirac Fermions and Superconductivity in the Homologous Structures (Ag xpb 1 xse) 5(Bi 2Se 3) 3m (m = 1, 2), Phys. Rev. B, 2014, 90, A newly discovered topological insulator (TI) (Ag xpb 1 xse) 5(Bi 2Se 3) 3m (m = 2) has a band gap of 0.5 ev, the largest value reported in topological insulators. We present a magnetotransport study of the Dirac electrons of this compound in the quantum diffusion regime. Two-dimensional weak antilocalization due to the destructive interference of the Dirac electronswas observed. The phase coherence length of the Dirac electrons is independent of doping and disorder levels. This provides an indication of the backscattering immunity under the protection of time reversal invariance of the TI. We further report that the homologous compound (Ag xpb 1 xse)5(bi 2Se 3) 3m (m = 1) is a superconductor with a transition temperature T C = 1.7 K. The related structures of these two phases allow lateral intergrowth of crystals to occur naturally, offering a potential platform to observe the Majorana fermion state at the boundary of two intergrown crystals. Διαλογή μονοκρυστάλλων, συλλογή δεδομένων περίθλασης ακτίνων-χ και επίλυση της κρυσταλλικής δομής των ημιαγώγων μικρού ενεργειακού χάσματος (Ag xpb 1 xse) 5(Bi 2Se 3) 3 και (Ag xpb 1 xse) 5(Bi 2Se 3) Στούμπος_Δημοσιεύσεις

44 44. A. Perivolaris, C. C. Stoumpos, J. Karpinska, A. G. Ryder, J. M. Frost, K. Mason, A. Prescimone, A. M. Z. Slawin, V. G. Kessler, J. S. Mathieson, L. Cronin, E. K. Brechin, G. S. Papaefstathiou, A Family of [Ni8] Cages Templated by μ6-peroxide from Dioxygen Activation, Inorg. Chem. Front., 2014, 1, A family of exceptionally thermally stable [Ni 8] cages is reported, each being templated by a rare η 3 :η 3 :μ 6-O 2 2 species produced by dioxygen activation, where the reducing agent for the O 2 reduction appears to be the ligand used in the reaction mixtures, which was found within the nickel cages in its oxidized form. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός της συμπλόκης ενώσης [Ni 8(O 2)(abmo) 6(4ClPhCO 2) 2(MeO) 6(MeOH) 2(H 2O) 2]. 44 Στούμπος_Δημοσιεύσεις

45 45. F. Hao, C. C. Stoumpos, R.P. H. Chang, M. G. Kanatzidis, Anomalous Band Gap Behavior in Mixed Sn and Pb Perovskites Enables Broadening of Absorption Spectrum in Solar Cells J. Am. Chem. Soc., 2014, 136, Perovskite-based solar cells have recently been catapulted to the cutting edge of thin-film photovoltaic research and development because of their promise for high-power conversion efficiencies and ease of fabrication. Two types of generic perovskites compounds have been used in cell fabrication: either Pbor Sn-based. Here, we describe the performance of perovskite solar cells based on alloyed perovskite solid solutions of methylammonium tin iodide and its lead analogue (CH 3NH 3Sn 1 xpb xi 3). We exploit the fact that, the energy band gaps of the mixed Pb/Sn compounds do not follow a linear trend (the Vegard s law) in between these two extremes of 1.55 and 1.35 ev, respectively, but have narrower bandgap (<1.3 ev), thus extending the light absorption into the nearinfrared ( 1,050 nm). A series of solution-processed solid-state photovoltaic devices using a mixture of organic spiro OMeTAD/lithium bis(trifluoromethylsulfonyl)imide/pyridinium additives as hole transport layer were fabricated and studied as a function of Sn to Pb ratio. Our results show that CH 3NH 3Sn 0.5Pb 0.5I 3 has the broadest light absorption and highest short circuit photocurrentdensity 20 ma. cm 2 (obtained under simulated full sunlight of 100 mw. cm 2 ). Σύνθεση και χαρακτηρισμός του ημιαγώγιμου, υβριδικού περοβσκιτικού στερεού διαλύματος CH 3NH 3Sn 1 xpb xi 3. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συν-συγγραφή του άρθρου. 45 Στούμπος_Δημοσιεύσεις

46 46. F. Hao, C. C. Stoumpos, D. Cao, R. P. H. Chang, M. G. Kanatzidis, Lead-Free Solid State Organic- Inorganic Halide Perovskite Solar Cells Nat. Photon., 2014, 8, Lead-free solution-processed solid-state photovoltaic devices based on methylammonium tin iodide (CH 3NH 3SnI 3) perovskite semiconductor as the light harvester are reported. Featuring an optical bandgap of 1.3 ev, the CH 3NH 3SnI 3 perovskite material can be incorporated into devices with the organic hole-transport layer spiro-ometad and show an absorption onset at 950 nm, which is significantly redshifted compared with the benchmark CH 3NH 3PbI 3 counterpart (1.55 ev). Bandgap engineering was implemented by chemical substitution in the form of CH 3NH 3SnI 3 xbr x solid solutions, which can be controllably tuned to cover much of the visible spectrum, thus enabling the realization of lead-free solar cells with an initial power conversion efficiency of 5.73% under simulated full sunlight. Further efficiency enhancements are expected following optimization and a better fundamental understanding of the internal electron dynamics and corresponding interfacial engineering. The reported CH 3NH 3SnI 3 xbr x perovskite solar cells represent a step towards the realization of low-cost, environmentally friendly solidstate solar cells. Σύνθεση και χαρακτηρισμός του ημιαγώγιμου, υβριδικού περοβσκιτικού στερεού διαλύματος CH 3NH 3SnI 3-xBr x. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών, πριν από την εναπόθεση τους σε λεπτά υμένια. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε πολυκρυσταλλικές σκόνες και λεπτά υμένια. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συν-συγγραφή του άρθρου. 46 Στούμπος_Δημοσιεύσεις

47 47. S. Wang, Z. Liu, J. A. Peters, M. Sebastian, S. L. Nguyen, C. D. Malliakas, C. C. Stoumpos, J. Im, A. J. Freeman, B. W. Wessels, M. G. Kanatzidis, Crystal Growth of Tl 4CdI 6: A Wide Band Gap Semiconductor for Hard Radiation Detection, Cryst. Growth Des., 2014, 14, We report the synthesis, physical characterization, and crystal growth of Tl 4CdI 6. We show that this material has good photoconductivity and is a promising semiconductor for room temperature X-ray and γ-ray detection. Large single crystals were grown by the vertical Bridgman method and cut to dimensions appropriate for detector testing. Single crystal X-ray diffraction refinements confirm that Tl 4CdI 6 crystallizes in the tetragonal crystal system with a centrosymmetric space group of P4/mnc, with a calculated density of 6.87 g/cm 3. Thermal analysis and high-temperature synchrotron powder diffraction studies were used to determine phase relationships and crystallization behavior during crystal growth. We have elucidated the reason for different colors encountered when synthesizing or growing single crystals of Tl 4CdI 6 (yellow, red, and black), and it is the presence of a small amount of TlI impurity. We report proper crystal growth conditions to obtain essentially pure yellow Tl 4CdI 6 crystals. The material having the yellow color has a band gap of 2.8 ev. First-principles density functional theory calculations indicate a direct band gap at the Γ point of the Brillouin zone. The Tl 4CdI 6 crystals have a resistivity of Ω cm. Photoconductivity measurements on the as-grown crystals show mobility-lifetime product on the order of 10 4 cm 2 /V for both electrons and holes. The promising detector properties of this material are confirmed by preliminary measurements showing a clear spectral response to an Ag X-ray source, which classifies Tl 4CdI 6 as an emerging material for radiation detection. Συλλογή και ανάλυση δεδομένων περίθλασης ακτίνων-χ πολυκρυσταλλικής σκόνης της ένωσης Tl 4CdI 6 με τη χρήση ακτινοβολίας σύγχροτρου για τον προσδιορισμό των ακαθαρσιών που εμφάνίζονται κατά τη διαδικασία ανάπτυξης μονοκρυστάλλων. 47 Στούμπος_Δημοσιεύσεις

48 48. F. Han, C. D. Malliakas, M. Sturza, C. C. Stoumpos, H. Claus, D.-Y. Chung, M. G. Kanatzidis, Superconductivity and Strong Intrinsic Defects in LaPd 1-xBi 2, Phys. Rev. B, 2013, 88, Two new phases LaPd 1 xbi 2 and CePd 1 xbi 2 were obtained by growing single crystals in Bi flux. They adopt the tetragonal ZrCuSi 2-type structure and feature Bi-square nets and PbO-type PdBi layers with significant partial Pd occupancy. Bulk superconductivity at 2.1 K and metallic behavior above Tc are observed in LaPd 1 xbi 2. A small residual resistance ratio (RRR) indicates a strong scattering effect induced by the Pd vacancies, which implies an s-wave pairing symmetry in LaPd 1 xbi 2. The broadening of the resistivity transition was measured under different magnetic fields demonstrating a high upper critical field of 3 T. Hall effect measurements reveal dominantly electron-like charge carriers and singleband transport behavior in LaPd 1 xbi 2. The paramagnetic CePd 1 xbi 2 is nonsuperconducting but shows antiferromagnetic ordering below 6 K. Διαλογή μονοκρυστάλλων, συλλογή δεδομένων περίθλασης ακτίνων-χ και επίλυση της κρυσταλλικής δομής των διαμεταλλικών ενώσεων LaPd 1 xbi 2 και CePd 1 xbi Στούμπος_Δημοσιεύσεις

49 49. Z. Liu, J. A. Peters, C. C. Stoumpos, M. Sebastian, B. W. Wessels, J. Im, A. J. Freeman, M. G. Kanatzidis, Heavy Metal Ternary Halides for Room-Temperature X-ray and Gamma-ray Detection, Proceedings of SPIE, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIV, 2013, 8852, 88520A A-7. We report our recent progress on wide bandgap ternary halide compounds CsPbBr 3 and CsPbCl 3 for room temperature x-ray and gamma-ray detectors. Their bandgaps are measured to be 2.24 ev and 2.86 ev, respectively. The measured mobility-lifetime products of CsPbBr 3 are , cm 2 /V, for electron and hole carriers, respectively, comparable to those of CdTe. We measured the room temperature spectral response of CsPbBr 3 sample to Ag Χ-ray radiation. It has a well-resolved spectral response to the 22.4 kev Kα radiation peak and detector efficiency comparable to that of CdZnTe detector at 295 K. Ανάπτυξη μονοκρυστάλλων των ημιαγώγιμων περοβσκιτικών ενώσεων CsPbCl 3 και CsPbBr 3. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε μονοκρυσταλλικά και πολυκρυσταλλικά δείγματα. Συλλογή κρυσταλλογραφικών δεδομένων και επίλυση κρυσταλλικής δομής. Φασματοσκοπικός χαρακτηρισμός του υλικού για την ανάπτυξή του ως ανιχνευτή ακτίνων-χ και ακτίνων-γ. 49 Στούμπος_Δημοσιεύσεις

50 50. C. C. Stoumpos, C. D. Malliakas, M. G. Kanatzidis, Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties, Inorg. Chem., 2013, 52, A broad organic inorganic series of hybrid metal iodide perovskites with the general formulation AMI 3, where A is the methylammonium (CH 3NH 3+ ) or formamidinium (HC(NH 2) 2+ ) cation and M is Sn (1 and 2) or Pb (3 and 4) are reported. The compounds have been prepared through a variety of synthetic approaches, and the nature of the resulting materials is discussed in terms of their thermal stability and optical and electronic properties. We find that the chemical and physical properties of these materials strongly depend on the preparation method. Single crystal X-ray diffraction analysis of 1 4 classifies the compounds in the perovskite structural family. Structural phase transitions were observed and investigated by temperaturedependent single crystal X-ray diffraction in the K range. The charge transport properties of the materials are discussed in conjunction with diffuse reflectance studies in the mid-ir region that display characteristic absorption features. Temperature-dependent studies show a strong dependence of the resistivity as a function of the crystal structure. Optical absorption measurements indicate that 1 4 behave as direct-gap semiconductors with energy band gaps distributed in the range of ev. The compounds exhibit an intense near-ir photoluminescence (PL) emission in the nm range ( ev) at room temperature. We show that solid solutions between the Sn and Pb compounds are readily accessible throughout the composition range. The optical properties such as energy band gap, emission intensity, and wavelength can be readily controlled as we show for the isostructural se ries of solid solutions CH 3NH 3Sn 1 xpb xi 3 (5). The charge transport type in these materials was characterized by Seebeck coefficient and Hall-effect measurements. The compounds behave as p- or n-type semiconductors depending on the preparation method. The samples with the lowest carrier concentration are prepared from solution and are n-type; p-type samples can be obtained through solid state reactions exposed in air in a controllable manner. In the case of Sn compounds, there is a facile tendency toward oxidation which causes the materials to be doped with Sn 4+ and thus behave as p-type semiconductors displaying metal-like conductivity. The compounds appear to possess very high estimated electron and hole mobilities that exceed 2000 cm 2 /(Vs) and 300 cm 2 /(Vs), respectively, as shown in the case of CH 3NH 3SnI 3 (1). We also compare the properties of the title hybrid materials with those of the all-inorganic CsSnI 3 and CsPbI 3 prepared using identical synthetic methods. Σύνθεση και χαρακτηρισμός των ημιαγώγιμων, υβριδικών περοβσκιτικών ενώσεων CH 3NH 3SnΙ 3, HC(NH 2) 2SnΙ 3, CsSnΙ 3, CH 3NH 3PbΙ 3, HC(NH 2) 2PbΙ 3, CsPbΙ 3 και του στερεού διαλύματος CH 3NH 3Sn 1 xpb xi 3. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων των υλικών. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε μονοκρυσταλλικά και πολυκρυσταλλικά δείγματα. Συλλογή κρυσταλλογραφικών δεδομένων και επίλυση κρυσταλλικής δομής. Χαρακτηρισμός με ηλεκτρονική μικροσκοπία σάρωσης. Συγγραφή του άρθρου. 50 Στούμπος_Δημοσιεύσεις

51 51. C. C. Stoumpos, C. D. Malliakas, J. A. Peters, Z. Liu, M. Sebastian, J. Im, T. C. Chasapis, A. C. Wibowo, D.-Y. Chung, A. J. Freeman, B. W. Wessels, M. G. Kanatzidis, Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection, Cryst. Growth Des., 2013, 13, The synthesis, crystal growth, and structural and optoelectronic characterization has been carried out for the perovskite compound CsPbBr 3. This compound is a direct band gap semiconductor which meets most of the requirements for successful detection of X- and γ-ray radiation, such as high attenuation, high resistivity, and significant photoconductivity response, with detector resolution comparable to that of commercial, state-of-the-art materials. A structural phase transition which occurs during crystal growth at higher temperature does not seem to affect its crystal quality. Its μτ product for both hole and electron carriers is approximately equal. The μτ product for electrons is comparable to cadmium zinc telluride (CZT) and that for holes is 10 times higher than CZT. Ανάπτυξη μονοκρυστάλλων της ημιαγώγιμης περοβσκιτικής ένωσης CsPbBr 3. Χαρακτηρισμός των θερμικών, οπτικών, ηλεκτρικών και φασματοσκοπικών ιδιοτήτων. Κρυσταλλογραφική ανάλυση με περίθλαση ακτίνων-χ σε μονοκρυσταλλικά και πολυκρυσταλλικά δείγματα. Συλλογή κρυσταλλογραφικών δεδομένων και επίλυση κρυσταλλικής δομής. Φασματοσκοπικός χαρακτηρισμός του υλικού για την ανάπτυξή του ως ανιχνευτή ακτίνων-χ και ακτίνων-γ. Συγγραφή του άρθρου. 51 Στούμπος_Δημοσιεύσεις

52 52. H. Sartzi, C. C. Stoumpos, M. Gkiouli, I. I. Verginadis, S. Ch. Karkabounas, L. Cunha-Silva, A. Escuer, S. P. Perlepes, The periodic table of di-2-pyridyl ketone: Vanadium complexes, Dalton Trans., 2012, 41, The reactions of VIV sources and di-2-pyridyl ketone have led to V IV 2, V V 2 and V V 4 complexes with interesting structures and properties. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός των συμπλόκων ενώσεων [V IV 2O 2(SO 4) 2{(py) 2C(OMe)(OH)} 2] 2MeOH, [V IV 2O 2(SO 4){( py) 2C(OMe)(O)} 2] 5MeOH, [V V 2O 2(O 2) 2{(py) 2C(OMe)(O)} 2] και [V V 4O 6(OMe) 4{(py) 2C(O) 2} 2]. 52 Στούμπος_Δημοσιεύσεις

53 53. C. C. Stoumpos, R. Inglis, O. Roubeau, H. Sartzi, A.A. Kitos, C. J. Milios, G Aromi, A. J. Tasiopoulos, V. Nastopoulos, E. K. Brechin, S.P. Perlepes, Rare Oxidation-State Combinations and Unusual Structural Motifs in Hexanuclear Mn Complexes Using 2-Pyridyloximate Ligands, Inorg. Chem., 2010, 49, The use of phenyl-2-pyridyl ketone oxime and di-2-pyridyl ketone oxime in Mn chemistry has led to hexanuclear clusters with unprecedented (Mn II 4Mn III Mn IV ) or extremely rare (Mn II Mn III 5 and Mn II 3Mn III 3) metal oxidation-state combinations and uncommon structural motifs. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός των ενώσεων [Mn II Mn III 5O 3(OEt) 0.5(N 3) 3(phpao) 6Br(EtOH) 1.5](Br) 0.5, [Mn II 4Mn III Mn IV O 2(O 2CPh) 6(phpao) 4](I 3). 3CH 2Cl 2 και [Mn II 3Mn III 3O 2(O 2CPh) 6(pypao) 2(dpk. OH) 2](ClO4). 1.5H 2O. Συν-συγγραφή του άρθρου. 53 Στούμπος_Δημοσιεύσεις

54 54. R. Inglis, C. C. Stoumpos, A. Prescimone, M. Siczek, T. Lis, W. Wernsdorfer, E. K. Brechin, C. J. Milios, Ferromagnetic Manganese "cubes": from PSII to single-molecule magnets, Dalton Trans., 2010, 39, The reaction of Mn(O 2CMe) 2 2H 2O with Me-saoH 2 (Me-saoH 2= 2-hydroxyphenylethanone oxime) in MeCN forms the complex [Mn III 4(Me-sao) 4(Me-saoH) 4] (1) in good yields. Replacing Me-saoH 2 with Naphth-saoH 2 (Naphth-saoH 2 = 2-hydroxy-1-napthaldoxime) in the presence of CH 3ONa forms the complex [Mn III 4(Naphth-sao) 4(Naphth-saoH) 4] (2) in low yields, while the reaction between Mn(ClO 4) 2 6H 2O, Et-saoH 2 (Et-saoH 2= 2-hydroxypropiophenone oxime) and NBu 4OH in MeCN gives the complex [Mn III 4(Et-sao) 4(Et-saoH) 4] (3) in moderate yields. All three tetrametallic cages exclusively contain Mn III centres arranged in a cube -like topology, in which the metal centres are connected by N O oximate groups. The magnetic properties of 1 3 are near identical, revealing the presence of only ferromagn etic interactions between the metal ions leading to high-spin ground states of S = 8. The complexes display frequency dependent out-of-phase signals in ac susceptibility studies and, in the case of 1 single-molecule magnetism has been observed by means of single-crystal hysteresis loop measurements. Σύνθεση, απομόνωση, μαγνητικός και φασματοσκοπικός χαρακτηρισμός της ένωσης [Mn III 4(Naphthsao) 4(Naphth-saoH) 4]. Συν-συγγραφή του άρθρου. 54 Στούμπος_Δημοσιεύσεις

55 55. C. C. Stoumpos, O. Roubeau, G. Aromi, A. J. Tasiopoulos, V. Nastopoulos, A. Escuer, S. P. Perlepes, The Depolymerization Approach in Mn Cluster Chemistry: Controlled Cleavage of an 1D Coordination Polymer Consisting of Mn 8 Units into its Constituent, Discrete Mn 8 Complex, Inorg. Chem., 2010, 49, The cleavage of a 1D coordination polymer (Mn II 2Mn III 6) n containing recognizable octanuclear units to obtain the discrete Mn II 2Mn III 6 cluster is reported. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός της ένωσης [Mn II 2Mn III 6O 2{(py) 2CO 2} 4{(py) 2C(OMe)O} 2(O 2CEt) 8] και του μονοδιάστατου πολυμερούς ένταξης [Mn II 2Mn III 6O 2{(py) 2CO 2} 4{(py) 2C(OMe)O} 2(O 2CEt) 6(HCO 2)] n(clo 4) n. nmeoh. 2nH 2O και μελέτη σχετικά με τη αλληλομετατροπή τους. Συν-συγγραφή του άρθρου. 55 Στούμπος_Δημοσιεύσεις

56 56. E. Manolopoulou, C. C. Stoumpos, M. Siczek, T. Lis, E. K. Brechin, C. J. Milios, Naked [Mn 3O] 7+ Triangles: The Effect of Auxilliary Ligands on Magnetic Exchange, Eur. J. Inorg. Chem., 2010, The reaction between Mn(ClO 4) 2 6H 2O, EtsaoH 2 (Et-saoH 2 = 2-hydroxypropiophenone oxime), NEt 4OH and [Ni(pao) 2(py) 2] (paoh = 2-pyridylaldoxime) in MeOH forms the complex [Mn III 3O(Et-sao) 3(HCO 2)(MeOH) 5] (1) in good yields. The reaction of MnCl 2 4H 2O, Me-saoH 2 (Me-saoH 2 = 2- hydroxyphenylethanone oxime), NEt 4OH and DL-valine in MeOH gives the complex [Mn III 3O(Me-sao) 3(MeOH )5]Cl (2) in moderate yields. In both complexes the building block consists of a triangular {Mn III 3O(R-sao) 3} unit (R = Et, Me for 1 and 2, respectively). In the case of 2, the [Mn 3] unit can be considered naked as there is no capping ligand present, whereas in the case of 1 a formate ion is terminally bonded to one metal centre. DC magnetic susceptibility measurements for 1 and 2 reveal the presence of both ferromagnetic and antiferromagnetic intramolecular interactions, depending on the Mn N O Mn torsion angles within each cluster, leading to a ground state S = 2 for both complexes. Rationalization of this result is attempted by structural comparison of previously reported triangular [Mn 3] oximate complexes on the basis of flat and twisted torsion angles and the effect of the auxiliary ligands. Σύνθεση, απομόνωση, μαγνητικός και φασματοσκοπικός χαρακτηρισμός της ένωσης [Mn III 3O(Etsao) 3(HCO 2)(MeOH) 5]. Συν-συγγραφή του άρθρου. 56 Στούμπος_Δημοσιεύσεις

57 57. H. Sartzi, G. S. Papaefstathiou, V. Psycharis, A. Escuer, S. P. Perlepes, C. C. Stoumpos, Halo and Azido Cu(II) Coordination Polymers Featuring the gem-diolate Forms of Di-2-Pyridyl Ketone, Polyhedron, 2010, 29, The reactions of di-2-pyridyl ketone, (py) 2CO, with [Cu 2(O 2CMe) 4(H 2O) 2] in the presence of NaN 3, HCl and HBr have led to the isolation of complexes {[Cu 8{(py) 2CO 2} 4(N 3) 6(O 2CMe) 2]. 2MeCN. H 2O} (1. 2MeCN. H 2O), [Cu 2{(py) 2C(OH)O}Cl 3] (2) and [Cu 2{(py) 2C(OH)O}Br 3] (3), respectively, where (py) 2CO 2 2- and (py) 2C(OH)O - are the dianion and the monoanion of the gem-diol form of (py) 2CO. Complex 1. 2MeCN. H 2O is an 1D coordination polymer consisting of centrosymmetric [Cu 8{(py) 2CO 2} 4(N 3) 6(O 2CMe) 2] cluster units linked through weakly coordinated azido bridges. The (py) 2CO 2 2- groups adopt the η 1 :η 2 :η 2 :η 1 :μ 4 coordination mode, while the N 3 - ions behave as η 2 :μ and η 1 : η 2 :μ 3 ligands. The isostructural compounds 2 and 3 are also1dβcoordination polymers consisting of {Cu 2{(py) 2C(OH)O}X 3} 2 units (X=Cl, Br) linked through double halo bridges. The (py) 2C(OH)Oligand adopts the tri- dentate, bis-chelating η 1 :η 2 :η 1 :μ mode. A common feature in the three complexes is the presence of interchain H- bonding interactions which result in the formation of 2D networks. The magnetic properties of 1 3 have been studied by variabletemperature dc magnetic susceptibility and variable-field magne- tization techniques. The analyses of the magnetic data were performed taking into account only the dominant exchange interactions within dinuclear subunits. The intradinuclear exchange interactions have been found to vary from strongly and moderately antiferromagnetic in 1 to ferromagnetic in 2 and 3. This work demonstrates the flexibility, versatility and synthetic potential of combining (py)2co with carboxido or halo ligands. Σύνθεση, απομόνωση, φασματοσκοπικός και μαγνητικός χαρακτηρισμός των μονοδιάστατων (1D) πολυμερών ένταξης {[Cu 8{(py) 2CO 2} 4(N 3) 6(O 2CMe) 2]. 2MeCN. H 2O}, [Cu 2{(py) 2C(OH)O}Cl 3] και [Cu 2{(py) 2C(OH)O}Br 3] και προσομοίωση της μαγνητικής συμπεριφοράς του συμπλόκου [Mn 4(O 2CPh) 4{(py) 2C(OH)O} 4]. Συγγραφή του άρθρου. 57 Στούμπος_Δημοσιεύσεις

58 58. T. C. Stamatatos, C. G. Efthymiou, C. C. Stoumpos, S. P. Perlepes, Adventures in the Coordination Chemistry of Di-2-pyridyl Ketone and Related Ligands: From High-Spin Molecules and Single-Molecule Magnets to Coordination Polymers, and from Structural Aesthetics to an Exciting New Reactivity Chemistry of Coordinated Ligands, Eur. J. Inorg. Chem., 2009, The coordination chemistry of di-2-pyridyl ketone and related ligands is reviewed. An outline of the variety of such igands is presented. References are given to methods for the synthesis of ligands that are not available on the market. The activation of the carbonyl group(s) of some of the ligands towards further reactions seems to be an emergent area of synthetic inorganic chemistry. The coordination chemistry of each ligand with metals is briefly described. Emphasis is placed on structural features and physical properties (mainly magnetic) of the resulting metal clusters and coordination polymers. The structural diversity of the complexes stems from the ability of the deprotonated diol- or hemiketal-type ligands to adopt a variety of bridging coordination modes depending on the number of carbonyl groups, the nature of the extra donor groups in the molecule and on the reaction conditions. Employment of a second organic or inorganic ligand in this chemistry gives an extraordinary structural flexibility in the resulting mixed-ligand systems. The initial use of 1,1,- carbonyldiimidazole and 1,1,-oxalyldiimidazole in copper(ii) chemistry, which leads to unprecedented coordination polymers containing alcoholysis and/or hydrolysis fragments of the ligands, is also illustrated. Συν-συγγραφή του άρθρου ανασκόπησης. 58 Στούμπος_Δημοσιεύσεις

59 59. C. C. Stoumpos, N. Lalioti, I. A. Gass, K. Gkotsis, A. A. Kitos, H. Sartzi, C. J. Milios, C. P. Raptopoulou, A. Terzis, E. K. Brechin, S. P. Perlepes, Linear Mn II 3 and Cubane Mn II 4 Carboxylate Clusters Derived from Di-2-Pyridyl Ketone: Synthesis, Characterization and Magnetic Properties, Polyhedron, 2009, 28, The employment of di-2-pyridyl ketone, (py) 2CO, in manganese(ii) benzoate chemistry is reported. The syntheses, crystal structures and spectroscopic (IR, EPR) characterization are described for [Mn II 3(O 2CPh) 6{(py) 2CO} 2] (1), [Mn II 3 (O 2CPh) 6{(py) 2CO} 2]. 2MeCN (2. 2MeCN) and [Mn II 4(O 2CPh) 4{(py) 2-C(OH)O} 4] (3), where (py) 2C(OH)O - is the monoanion of the gem-diol form of (py) 2CO. Variable-temperature, magnetic susceptibility studies on 3 have also been performed. Complexes 1 and 2. 2MeCN are linkage isomers. The trinuclear molecules of both complexes have a linear structure, with one η 1 :η 2 :μ and two syn, syn- η 1 :η 1 :μ PhCO 2 - groups spanning each pair of Mn II atoms. The terminal Mn II atoms are each capped by one κ 2 N,N (py) 2CO ligand in orange 1 and one κ 2 N,Ο (py) 2CO molecule in the yellow isomer 2. 2MeCN. The molecule of 3 has a cubane topology with the Mn II centers and the deprotonated oxygen atoms from the η 1 :η 3 :η 1 :μ 3 ligands occupying alternate vertices of the cube. A terminal monodentate PhCO 2 - group completes a distorted octahedral coordination at each Mn II atom. The IR data are discussed in terms of the coordination modes of the ligands that are present in the complexes. The X- band EPR spectra of powdered 1 and 2 at 4 K indicate that the populated spin states exhibit a zero-field splitting, while the spectrum of 3 at 18 K is consistent with the presence of magnetically interacting Mn II atoms in the solid state. The magnetic properties of 3 in the K range have been modelled with two J values, which reveal weak antiferromagnetic interactions within the molecule. Some suggestions have been made concerning the great stability of complex 3. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός των ενώσεων [Mn 3(O 2CPh) 6{(py) 2CO} 2] και [Mn 4(O 2CPh) 4{(py) 2C(OH)O} 4] και προσομοίωση της μαγνητικής συμπεριφοράς του συμπλόκου [Mn 4(O 2CPh) 4{(py) 2C(OH)O} 4]. Συν-συγγραφή του άρθρου. 59 Στούμπος_Δημοσιεύσεις

60 60. G. Karotsis, C. C. Stoumpos, A. Collins, F. White, S. Parsons, A. M. Z. Slawin, G. S. Papaefstathiou, E. K. Brechin, Molecular and Supramolecular Ni(II) Wheels from α-benzoin Oxime, Dalton Trans., 2009, The use of a benzoin oxime in Ni(II) chemistry leads to the formation of a family of unusual molecular and supramolecular wheels. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός της συμπλόκης ενώσης [Ni 8(abo) 8(Et 2O) 2(MeOH) 2(H 2O)] 2Et 2O. 60 Στούμπος_Δημοσιεύσεις

61 61. C. C. Stoumpos, T. C. Stamatatos, H. Sartzi, O. Roubeau, A. J. Tasiopoulos, V. Nastopoulos, S. J. Teat, G. Christou, S. P. Perlepes, Employment of Methyl 2-Pyridyl Ketone Oxime in Manganese Non-Carboxylate Chemistry: Mn II 2Mn IV and Mn II 2Mn III 6 Complexes, Dalton Trans., 2009, The employment of the anion of methyl 2-pyridyl ketone oxime (mpko-) as a tridentate chelating/ bridging ligand in manganese chemistry is described. The inorganic anion (Br -, ClO 4 - ) used in the reaction affects the identity of the product. The reaction of MnBr 2 and one equivalent of mpkoh in the presence of a base affords [Mn 3(OMe) 2(mpko) 4Br 2] (3), which is mixed-valence (2Mn II, Mn IV ). The central Mn IV atom in each of the two, crystallographically independent, centrosymmetric molecules is coordinated by four oximate oxygen atoms belonging to the η 1 :η 1 :η 1 :μ mpko - ligands, and two η 1 :μ MeO - groups, while six coordination at each terminal Mn II atom is completed by four nitrogen atoms belonging to the chelating part of two mpko- ligands, and one Br- ion. The Mn II atoms have trigonal prismatic coordination geometry. The reaction of Mn(ClO 4) 2 6H 2O, mpkoh and OH - (1:2:1) in MeOH gives [Mn 8O 4(OMe)(mpko) 9(mpkoΗ)](ClO 4) 4 (4), which is also mixed-valence (2Mn II, 6Mn III ) and possesses the novel [Mn8(μ 3-O) 4(μ-OMe)(μ-OR ) 2] 11+ core. The latter possesses a U-shaped sequence of four fused {Mn II Mn III 2(μ 3-O)} 6+ triangular units, with a Mn III -Mn III edge being shared between the central triangles. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on complexes 3 and 4. The dc susceptibility data for 3 in the K range have been fit to a model with two J values, revealing weak ferromagnetic MnII MnIV (J = +3.4 cm-1) and MnII MnII (J = +0.3 cm -1 ) exchange interactions. Fitting of the magnetization vs. H/T data by matrix diagonalization and including only axial anisotropy (ZFS, D) gave ground state spin (S) and D values of S = 13/2, D = cm -1 for 3 and S = 3, D = cm -1 for 4. The combined work demonstrates the usefulness of mpko - in the preparation of interesting Mn clusters, without requiring the co-presence of carboxylate ligands. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός των συμπλόκων ενώσεων [Mn 3(OMe) 2(mpko) 4Br 2] και [Mn 8O 4(OMe)(mpko) 9(mpkoΗ)](ClO 4) 4. Συν-συγγραφή του άρθρου. 61 Στούμπος_Δημοσιεύσεις

62 62. C. C. Stoumpos, R. Inglis, G. Karotsis, L. F. Jones, A. Collins, S. Parsons, C. J. Milios, G. S. Papaefstathiou, E. K. Brechin, Supramolecular Entanglement from Interlocked Molecular Nanomagnets, Cryst. Growth Des., 2009, 9, The trinuclear nanomagnet [Mn III 3O(Et-sao) 3(MeOH) 3](ClO 4) (1) has been utilized as a building block for the construction of the hexanuclear cluster [{Mn ΙΙΙ 3O(Et-sao) 3(O 2CPh)(EtOH)} 2{4,4 - bpe} 2] 2 (3) that conforms to a rectangle and the two-dimensional coordination polymer {[Mn III 3O(sao) 3(4,4 -bpe) 1.5]ClO 4 3MeOH} n (2 3MeOH). The latter exhibits an unprecedented type of entanglement that is based on host guest interactions. The polygon versus the polymer is rationalized in terms of changing an auxiliary anion that influences the arrangement of the potentially vacant coordination axes on each Mn III ion of the trinuclear precursor and thereby directing the self-assembly process. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός των συμπλόκων ενώσεων [Mn III 3O(Et-sao) 3(MeOH) 3](ClO 4) και [{Mn ΙΙΙ 3O(Et-sao) 3(O 2CPh)(EtOH)} 2{4,4 -bpe} 2] 2 και του δι-διαστατου (2D) πολυμερούς ένταξης{[mn III 3O(sao) 3(4,4 - bpe) 1.5]ClO 4 3MeOH} n. Συν-συγγραφή του άρθρου. 62 Στούμπος_Δημοσιεύσεις

63 63. C. C. Stoumpos, I. A. Gass, C. J. Milios, N. Lalioti, A. Terzis, G. Aromi, S. J. Teat, E. K. Brechin, S. P. Perlepes, A Mn II 4 Cubane and a Novel Mn II 10Mn III 4 Cluster from the Use of Di-2-Pyridyl Ketone in Manganese Acetate Chemistry, Dalton Trans., 2009, The employment of di-2-pyridyl ketone, (py)2co, in manganese(ii) acetate chemistry is reported. The syntheses, crystal structures and magnetochemical characterisation are described for [Mn 4(O 2CMe) 4{(py) 2C(OH)O} 4] (1) and [Mn II 10Mn III 4O 4(O 2CMe) 20{(py) 2C(OH)O} 4] (2), where {(py) 2C(OH)O - is the monoanion of the gem-diol form of the ligand. The reaction of Mn(O2CMe) 2 4H2O with one equivalent of (py) 2CO in Me 2CO gives 1. Complex 2 was obtained from the 1 :1 reaction, in EtOH, between Mn(O 2CMe) 2 4H 2O and (py) 2CO in the presence of NΕt 3. The tetranuclear molecule 1 has a cubane topology with the Mn II and the deprotonated oxygen atoms from the η 1 :η 3 :η 1 :μ 3 ligands occupying alternate vertices of the cube. The core of 2 consists of two mixed valence cubane {Mn II 2Mn III 2(μ 3-O) 2(μ 3- OR ) 2} 4+ subunits that are linked through an unusual {Mn II 6(η 2 :η 2 :μ-o 2CMe) 6(η 2 : η 2 :μ 3-O 2CMe) 2} 4+ moiety via twelve η 1 :η 1 : μ MeCO - 2 groups. Some suggestions have been made concerning the possible assembly of 2 from 1. The magnetic properties of 1 in the K range have been modelled with two J values, which reveal weak antiferromagnetic interactions within the molecule. Complex 2 has a low spin ground state. This work demonstrates the flexibility, versatility and synthetic potential of combining (py) 2CO with carboxylate ligands. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός των ενώσεων [Mn 4(O 2CMe) 4{(py) 2C(OH)O} 4] και [Mn II 10Mn III 4O 4(O 2CMe) 20{(py) 2C(OH)O} 4] και προσομοίωση της μαγνητικής συμπεριφοράς του συμπλόκου [Mn 4(O 2CMe) 4{(py) 2C(OH)O} 4]. Συν-συγγραφή του άρθρου. 63 Στούμπος_Δημοσιεύσεις

64 64. C. C. Stoumpos, T. C. Stamatatos, V. Psycharis, C. P. Raptopoulou, G. Christou, S. P. Perlepes, A New Mn II 4Mn III 4 Cluster from the Use of Methyl 2-Pyridyl Ketone Oxime in Manganese Carboxylate Chemistry: Synthetic, Structural and Magnetic Studies, Polyhedron, 2008, 27, The use of methyl 2-pyridyl ketone oxime (mpkoh) in manganese benzoate chemistry is reported. The reaction of Mn(O 2CPh) 2 2H 2O with two equivalents of mpkoh in CH 2Cl 2 affords the mononuclear complex [Mn II (O 2CPh) 2(mpkoH) 2] (2) in high yield. The Mn II atom is coordinated by two monodentate - PhCO 2 groups and two N,N -bidentate mpkoh chelates in a cis cis trans fashion. Reaction mixtures comprising (NBu n 4)[Mn III 4O 2(O 2CPh) 9(H 2O)] and mpkoh in CH 2Cl 2, [Mn II Mn III 2O(O 2CPh) 6(py) 2(H 2O)] and mpkoh in CH 2Cl 2, or Mn(O 2CPh) 2 2H 2O, NBu n MnO4 and mpkoh in MeOH/MeCN/CH 2Cl 2 all lead to the mixed- alent cluster [Mn II 4 Mn III 4O 2(OH) 2(O 2CPh) 10(mpko) 4] (3) in moderate yields. The cluster molecule has the [Mn 8(μ 4-O) 2(μ 3- OH) 2] 14+ core (another description of the core is [Mn 8(μ 4-O) 2(μ 3-OH) 2(μ- OR ) 4(μ-ONR ) 4] 6+ ). Peripheral ligation is provided by two η 1, four η 1 : η 1 :μ and four η 1 : η 1 - :μ 3 PhCO 2 groups, as well as four η 1 : η 1 : η 1 :μ mpko - ligands. Variable-temperature, solid-state dc and ac magnetic studies were carried out on complex 3 in the K (dc) and K (ac) ranges. The data reveal dominant antiferromagnetic interactions and a resultin S = 0 ground state, which is rationalized in terms of the strong antiferromagnetic coupling within the central {Mn III 2 O 2} 2+ subunit. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός των συμπλόκων ενώσεων [[Mn II (O 2CPh) 2(mpkoH) 2] και [Mn II 4 Mn III 4O 2(OH) 2(O 2CPh) 10(mpko) 4]. Συν-συγγραφή του άρθρου. 64 Στούμπος_Δημοσιεύσεις

65 65 C. C. Stoumpos, E. Diamantopoulou, C. P. Raptopoulou, A. Terzis, S. P. Perlepes, N. Lalioti, A Two-Dimensional Manganese(II) Coordination Polymer Containing 1-Hydroxybenzotriazolate and Acetate Bridging Ligands: Preparation, Structural Characterization and Magnetic Study, Inorg. Chim. Acta., 2008, 361, The initial use of the 1-hydroxybenzotriazolate (btao - )/acetate ligand blend in manganese(ii) chemistry has yielded a neutral 2D coordination polymer. Complex [Mn II 3(O 2CMe) 2(btaO) 4(MeOH) 2] n was prepared by the reaction of Mn(O 2CMe) 2. 4H 2O with btaoh in MeOH. The structure is based on centrosymmetric trinuclear units, which create the 2D network via and (Harris notation) btao - ligands. The two crystallographically independent MnII ions within - the trinuclear unit are bridged by one 2.11 MeCO 2 group and two btao - ligands. Characteristic IR bands are discussed in terms of the coordination modes of the ligands. The intra- (J 1 = -3.7 cm -1 ) and inter (J 2 = J3 = -0.2 cm -1 ) magnetic exchange coupling constants have been obtained from Monte Carlo calculations. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός του πολυμερους ένταξης [Mn II 3(O 2CMe) 2(btaO) 4(MeOH) 2] n. Συν-συγγραφή του άρθρου. 65 Στούμπος_Δημοσιεύσεις

66 66. C. C. Stoumpos, I. A. Gass, C. J. Milios, E. Kefalloniti, C. P. Raptopoulou, A. Terzis, N. Lalioti, E. K. Brechin, S. P. Perlepes, The Use of Di-2-Pyridyl Ketone in Manganese(II) Benzoate Chemistry: Two Novel Mn II 3 Linkage Isomers Containing the Ketone Form of the Ligand and a Neutral Mn II 4 Cubane Containing the Ligand in its Gem-Diolate(-1) Form, Inorg. Chem. Commun., 2008, 11, The use of di-2-pyridyl ketone, (py) 2CO, in manganese(ii) benzoate chemistry has yielded two Mn II 3 linkage isomers containing the ketone form of the ligand and a neutral MnII4 cubane cluster containing the gem-diolate(-1) form of the ligand. The 3:2 Mn(O 2CPh) 2. 2H 2O/(py) 2CO reaction system in MeCN gives a mixture of the orange complex [Mn 3(O 2CPh) 6{(py) 2CO-κ 2 N,N } 2] (1) and the yellow compound [Mn 3(O 2CPh) 6{(py) 2CO-κ 2 N,O} 2]. 2MeCN (2. 2MeCN). The known compound [Mn 6O 2(O 2CPh) 10(MeCN) 4] (3) appears as a by-product when the initial reaction solution, that leads to 1 and 2. 2MeCN, is allowed to slowly evaporate in the air. The trinuclear molecules adopt a linear structure in both complexes, with one monoatomically bridging η 1 : η 1 :μ and two syn,syn η 1 : η 1 :μ carboxylate groups spanning each pair of MnII ions. The terminal Mn II ions are each capped by one chelating-n,n (py) 2CO ligand in 1 and by one chelating-n,o (py) 2CO molecule in 2. The 1:1 reaction of Mn(O 2CPh) 2. 2H 2O and (py) 2CO in CH 2Cl 2 results in the isolation of [Mn 4(O 2CPh) 4{(py) 2C(OH)O} 4] (4). The tetranuclear molecule has a cubane topology with the Mn II ions and the deprotonated oxygen atoms from the (py) 2C(OH)O - ligands occupying alternate vertices. The IR data are discussed in terms of the nature of the bonding. The magnetic properties of 4 in the K range have been modeled with two J values and reveal weak intramolecular antiferromagnetic interactions. The low temperature X-band EPR spectra of 1, 2 and 4 are also discussed. Σύνθεση, απομόνωση και φασματοσκοπικός χαρακτηρισμός των ενώσεων [Mn 3(O 2CPh) 6{(py) 2CO} 2] και [Mn 4(O 2CPh) 4{(py) 2C(OH)O} 4] και προσομοίωση της μαγνητικής συμπεριφοράς του συμπλόκου [Mn 4(O 2CPh) 4{(py) 2C(OH)O} 4]. Συν-συγγραφή του άρθρου. 66 Στούμπος_Δημοσιεύσεις