N. Benmekideche, Sabah Fetah, Gh. Belgoumri
et al.
In this paper, we studied the structural, electronic and some optical properties of KGaQ2 (Q = S, Se) and AGaTe2 (A = K, Cs) crystals using the pseudopotential plane-wave (PP-PW) method based on density functional theory (DFT), the generalized gradient approximation (GGA) parameterized by Perdew-Burke-Ernzerhof (GGA-PBE) is used for the exchange – correlation (XC) potential. We also use the hybrid density functional (HSE06) to study the electronic structures of these materials. Our results for the equilibrium lattice constants (a, b and c), angle β are in good agreement with experiment data. The electronic structure calculation suggested that crystals are direct-gap semiconductors, employing both the Perdew–Burke–Ernzerhof (PBE) and the hybrid (HSE06) functionals. We note that the hybrid density functional improved the value of band gap, and that the studied compounds are semiconductors with wide band gaps. We have also predicted the optical properties; the refractive index, the reflection coefficient and dielectric constant on high frequencies.
AbstractThe novel host–guest compound [Cs6Cl][Fe24Se26] (I4/mmm; a=11.0991(9), c=22.143(2) Å) was obtained by reacting Cs2Se, CsCl, Fe, and Se in closed ampoules. This is the first member of a family of compounds with unique Fe–Se topology, which consists of edge‐sharing, extended fused cubane [Fe8Se6Se8/3] blocks that host a guest complex ion, [Cs6Cl]5+. Thus Fe is tetrahedrally coordinated and divalent with strong exchange couplings, which results in an ordered antiferromagnetic state below TN=221 K. At low temperatures, a distribution of hyperfine fields in the Mössbauer spectra suggests a structural distortion or a complex spin structure. With its strong Fe–Se covalency, the compound is close to electronic itinerancy and is, therefore, prone to exhibit tunable properties.
AbstractCs2Ga2Se5 was obtained by the reaction of CsN3 with stoichiometric amounts of GaSe and Se at elevated temperature. It forms yellow crystals embedded in a pure orange microcrystalline powder. The crystal structure of Cs2Ga2Se5 was determined by single‐crystal X‐ray diffraction at 123 K. The compound crystallizes monoclinically in the space group C2/c (No. 15) with a = 15.3911(5) Å, b = 7.3577(2) Å, c = 12.9219(3) Å, β = 126.395(3)°, V = 1177.89(7) Å3, and Z = 4. The structure features one‐dimensional chains 1∞[Ga2Se3(Se2)2–], consisting of edge‐ and corner sharing GaSe4 tetrahedra. Raman spectroscopic measurements reveal vibrational bands of the Se22– units at 236 cm–1, and the bands of Ga–Se vibrations at 254 and 273 cm–1. UV/Vis diffuse reflectance spectroscopy shows the bandgap at about 1.95 eV.
Paula M. Briggs Piccoli, Kent D. Abney, Jon R. Schoonover
et al.
AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Арнольд Юхимович Ків, Сергій Олексійович Семеріков, Володимир Миколайович Соловйов
et al.
Proceedings of the 4th Workshop for Young Scientists in Computer Science & Software Engineering (CS&SE@SW 2021), Virtual Event, Kryvyi Rih, Ukraine, December 18, 2021
Abstract Hydrothermal reaction of Ge and Se with Ag(CH3COO) in the presence of alkali metal carbonates affords the open framework selenidogermanates(IV) A3[AgGe4Se10]·2H2O (A = Rb, Cs), 1 and 2, which contain corner linked adamantane-like Ge4Se10 cages and AgSe4 tetrahedra. The analogous reaction with Mn(CH3COO)2 yields the isostructural tetragonal compounds A2[MnGe4Se10]·3H2O (A = Rb, Cs), 3 and 4. The cations are sited at a general position in the channels of the silver bridged anionic framework of 1 and 2 and exhibit a disordered pattern of occupation (s.o.f. = 0.75) with one of the two crystallographically independent water oxygen atoms O(2) (s.o.f. = 0.25). In contrast, the Rb+ cations in 3 are disordered over all three cation/oxygen sites, and the cation/water occupation pattern is fully reversed for the larger Cs+ cations in 4 in comparison to 1 and 2.