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Layered chalcogenides containing 3d transition metals are promising for the development of two-dimensional nanomaterials with interesting magnetic properties. Both mechanical and solution-based exfoliation of atomically thin layers is possible due to the low-energy van der Waals bonds. In this paper, we present the synthesis and crystal structures of the Mn 2 Ga 2 S 5 and Mn 2 Al 2 Se 5 layered chalcogenides. For Mn 2 Ga 2 S 5 , we report magnetic properties, as well as the exfoliation of nanofilms and nanoscrolls. The synthesis of both polycrystalline phases and single crystals is described, and their chemical stability in air is studied. Crystal structures are probed via powder X-ray diffraction and high-resolution transmission electron microscopy. The new compound Mn 2 Al 2 Se 5 is isomorphous with Mn 2 Ga 2 S 5 crystallizing in the Mg 2 Al 2 Se 5 structure type. The crystal structure is built by the ABCBCA sequence of hexagonal close-packing layers of chalcogen atoms, where Mn 2+ and Al 3+ /Ga 3+ species preferentially occupy octahedral and tetrahedral voids, respectively. Mn 2 Ga 2 S 5 exhibits an antiferromagnetic-like transition at 13 K accompanied by the ferromagnetic hysteresis of magnetization. Significant frustration of the magnetic system may yield spin-glass behavior at low temperatures. The exfoliation of Mn 2 Ga 2 S 5 layers was performed in a non-polar solvent. Nanolayers and nanoscrolls were observed using high-resolution transmission electron microscopy. Fragments of micron-sized crystallites with a thickness of 70-100 nanometers were deposited on a glass surface, as evidenced by atomic force microscopy.

In searching for a tool for optimizing the band gap of a hybrid compound capable of serving as a light-harvesting material in lead-free photovoltaics, we synthesized a new polyiodoantimonate (HpipeH 2 ) 2 [Sb 2 I 10 ](I 2 ) and analyzed its crystal and electronic structure by application of X-ray crystal structure analysis, Raman and diffuse reflectance spectroscopies, and quantum chemical calculations. It was demonstrated that I 2 molecules link Sb 2 I 10 edge-sharing octahedra into zig-zag chains, whereas the organic cations link inorganic anionic chains into a 3D structure featuring a complex pattern of covalent bonds and non-covalent interactions. Overall, these features provide the background for forming the electronic structure with a narrow band gap of 1.41 eV, therefore being a versatile tool for optimizing the band gap of a potential light-harvesting hybrid compound.

Metal gallium as a low-melting solid was applied in a mixture with elemental iodine to substitute tin(IV) in a promising light-harvesting phase of Cs 2 SnI 6 by a reactive sintering method. The reducing power of gallium was applied to influence the optoelectronic properties of the Cs 2 SnI 6 phase via partial reduction of tin(IV) and, very likely, substitute partially Sn 4+ by Ga 3+ . The reduction of Sn 4+ to Sn 2+ in the Cs 2 SnI 6 phase contributes to the switching from p -type conductivity to n-type, thereby improving the total concentration and mobility of negative-charge carriers. The phase composition of the samples obtained was studied by X-ray diffraction (XRD) and 119 Sn Mössbauer spectroscopy (MS). It is shown that the excess of metal gallium in a reaction melt leads to the two-phase product containing Cs 2 SnI 6 with Sn 4+ and β-CsSnI 3 with Sn 2+ . UV-visible absorption spectroscopy shows a high absorption coefficient of the composite material.

Despite remarkable progress in photoconversion efficiency, the toxicity of lead-based hybrid perovskites remains an important issue hindering their applications in consumer optoelectronic devices, such as solar cells, LED displays, and photodetectors. For that reason, lead-free metal halide complexes have attracted great attention as alternative optoelectronic materials. In this work, we demonstrate that reactions of two aromatic diamines with iodine in hydroiodic acid produced phenylenediammonium (PDA) and N,N-dimethyl-phenylenediammonium (DMPDA) triiodides, PDA(I 3 ) 2 ⋅2H 2 O and DMPDA(I 3 )I, respectively. If the source of bismuth was added, they were converted into previously reported PDA(BiI 4 ) 2 ⋅I 2 and new (DMPDA) 2 (BiI 6 )(I 3 )⋅2H 2 O, having band gaps of 1.45 and 1.7 eV, respectively, which are in the optimal range for efficient solar light absorbers. All four compounds presented organic-inorganic hybrids, whose supramolecular structures were based on a variety of intermolecular forces, including (N)H⋅⋅⋅I and (N)H⋅⋅⋅O hydrogen bonds as well as I⋅⋅⋅I secondary and weak interactions. Details of their molecular and supramolecular structures are discussed based on single-crystal X-ray diffraction data, thermal analysis, and Raman and optical spectroscopy.

Structure and properties of an inorganic perovskite Cs 2 SnI 6 demonstrated its potential as a light-harvester or electron-hole transport material; however, its optoelectronic properties are poorer than those of lead-based perovskites. Here, we report the way of light tuning of absorption and transport properties of cesium iodostannate(IV) Cs 2 SnI 6 via partial heterovalent substitution of tin for indium. Light absorption and optical bandgaps of materials have been investigated by UV-vis absorption and photoluminescent spectroscopies. Low-temperature electron paramagnetic resonance spectroscopy was used to study the kind of paramagnetic centers in materials., (Copyright © 2020 Umedov, Grigorieva, Lepnev, Knotko, Nakabayashi, Ohkoshi and Shevelkov.)

Exploiting a template effect of 1,4-diazacycloheptane (also known as homopiperazine, Hpipe), four new hybrid iodides, (HpipeH 2 ) 2 Bi 2 I 10 ·2H 2 O, (HpipeH 2 )I(I 3 ), (HpipeH 2 ) 3 I 6 ·H 2 O, and (HpipeH 2 ) 3 (H 3 O)I 7 , were prepared and their crystal structures were solved using single crystal X-ray diffraction data. All four solid-state crystal structures feature the HpipeH 2 2+ cation alternating with Bi 2 I 10 4- , I 3 - , or I - anions and solvent water or H 3 O + cation. HpipeH 2 2+ assembles anionic and neutral building blocks into polymer structures by forming four strong (N)H···I and (N)H···O hydrogen bonds per cation, with the H···I distances ranging from 2.44 to 2.93 Å and H···O distances of 1.88-1.89 Å. These hydrogen bonds strongly affect the properties of compounds; in particular, in the case of (HpipeH 2 ) 2 Bi 2 I 10 ·2H 2 O, they ensure narrowing of the band gap down to 1.8 eV and provide high thermal stability up to 240 °C, remarkable for a hydrated molecular solid.

In this paper, the potential existence of two-gap superconductivity in Mo 8 Ga 41 is addressed in detail by means of thermodynamic and spectroscopic measurements. A combination of highly sensitive bulk and surface probes, specifically ac-calorimetry and scanning tunneling spectroscopy (STS), are utilized on the same piece of crystal and reveal the presence of only one intrinsic gap in the system featuring strong electron-phonon coupling. Minute traces of additional superconducting phases detected by STS and also in the heat capacity measured in high magnetic fields on a high-quality and seemingly single-phase crystal might mimic the multigap superconductivity of Mo 8 Ga 41 suggested recently in several studies.

A series of substitutional solid solutions-Eu₇Cu 44- x T x As 23 (T = Fe, Co, Ni)-based on a recently discovered clathrate-like compound (Eu₇Cu 44 As 23 ) were synthesized from the elements at 800 °C. Almost up to 50% of Cu can be substituted by Ni, resulting in a linear decrease of the cubic unit cell parameter from a = 16.6707(1) Å for the ternary compound to a = 16.3719(1) Å for the sample with the nominal composition Eu₇Cu 24 Ni 20 As 23 . In contrast, Co and Fe can only substitute less than 20% of Cu. Crystal structures of six samples of different composition were refined from powder diffraction data. Despite very small differences in scattering powers of Cu, Ni, Co, and Fe, we were able to propose a reasonable model of dopant distribution over copper sites based on the trends in interatomic distances as well as on Mössbauer spectra for the iron-substituted compound Eu₇Cu 36 Fe₈As 23 . Ni doping increases the Curie temperature to 25 K with respect to the parent compound, which is ferromagnetically ordered below 17.5 K, whereas Fe doping suppresses the ferromagnetic ordering in the Eu sublattice.

Based on chemically synthesized powders of FeGa3, CoGa3, as well as of a Fe0.75Co0.25Ga3 solid solution, thin films (typical thickness 40 nm) were fabricated by flash evaporation onto various substrates held at ambient temperature. In this way, the chemical composition of the powders could be transferred one-to-one to the films as demonstrated by Rutherford backscattering experiments. The relatively low deposition temperature necessary for conserving the composition leads, however, to 'X-ray amorphous' film structures with immediate consequences on their transport properties: A practically temperature-independent electrical resistivity of ρ = 200 μΩ·cm for CoGa3 and an electrical resistivity of about 600 μΩ·cm with a small negative temperature dependence for FeGa3. The observed values and temperature dependencies are typical of high-resistivity metallic glasses. This is especially surprising in the case of FeGa3, which as crystalline bulk material exhibits a semiconducting behavior, though with a small gap of 0.3 eV. Also the thermoelectric performance complies with that of metallic glasses: Small negative Seebeck coefficients of the order of -6 μV/K at 300 K with almost linear temperature dependence in the range 10 K ≤ T ≤ 300 K.

The Re3As7- x In x solid solution was prepared for x ≤ 0.5 by heating the elements in stoichiometric ratios in evacuated silica tubes at 1073 K. It crystallizes with the Ir3Ge7 crystal structure, space group Im-3m, with a unit-cell parameter a ranging from 8.716 to 8.747 Å. The crystal structure and properties were investigated for a composition with x = 0.4. It is shown that indium substitutes arsenic exclusively at one crystallographic site, such that the As-As dumbbells with d As-As = 2.54 Å remain intact. Re3As6.6In0.4 behaves as a bad metal or heavily doped semiconductor, with electrons being the dominant charge carriers. It possesses high values of Seebeck coefficient and low thermal conductivity, but relatively low electrical conductivity, which leads to rather low values of the thermoelectric figure of merit.