Si extraction from silica in a basic polychalcogenide flux. Stabilization of Ba4SiSb2Se11, a novel mixed selenosilicate/selenoantimonate with a polar structure

Ba14Si4Sb8Te32(Te3): hypervalent Te in a new structure type with low thermal conductivity

Heavier pnictogen (Sb, Bi) containing chalcogenides are well known for their complex structures and semiconducting properties for numerous applications, particularly thermoelectric materials. Here, we report the syntheses of single crystals and polycrystalline phases of a new complex quaternary polytelluride, Ba14Si4Sb8Te32(Te3), via a high-temperature reaction of elements. A single-crystal X-ray diffraction study showed that it crystallizes in an unprecedented structure type with monoclinic symmetry (space group: P21/c). The crystal structure of Ba14Si4Sb8Te32(Te3) consists of one-dimensional ∞1[Si4Sb8Te32(Te3)]28- stripes, which are separated by the Ba2+ cations. Its complex structure features linear polytelluride units of Te34- having intermediate Te⋯Te interactions. A polycrystalline Ba14Si4Sb8Te32(Te3) sample shows a direct narrow bandgap of 0.8(2) eV, which indicates its semiconducting nature. The electrical resistivity of a sintered pellet of the polycrystalline sample exponentially decreases from ∼39.3 Ωcm to ∼0.57 Ωcm on heating it from 323 K to 773 K, confirming the sample's semiconducting nature. The sign of Seebeck coefficient values is positive in the 323 K to 773 K range confirming the p-type nature of the sintered sample. Interestingly, the sample attains an extremely low thermal conductivity of ∼0.32 Wm-1K-1 at 773 K, which could be attributed to the lattice anharmonicity caused by the lone pair effect of Sb3+ species in its complex pseudo-one-dimensional crystal structure. The electronic band structure of the title phase and the strength of chemical bonding of pertinent atomic pairs have been evaluated theoretically using the DFT method.

Germanium Antimony Bonding in Ba4Ge2Sb2Te10 with Low Thermal Conductivity

A new quaternary telluride, Ba₄Ge₂Sb₂Te₁₀, was synthesized at high temperature via the reaction of elements. A single-crystal X-ray diffraction study shows that the title compound crystallizes in its own structure type in the monoclinic P2₁/c space group having cell dimensions of a = 13.984(3) Å, b = 13.472(3) Å, c = 13.569(3) Å, and β = 90.16(3)° with four formula units per unit cell (Z = 4). The pseudo-one-dimensional crystal structure of Ba₄Ge₂Sb₂Te₁₀ consists of infinite ₁^∞[Ge₂Sb₂Te₁₀]^8- stripes, which are separated by Ba²⁺ cations. Each of the Ge(1) atoms is covalently bonded to four Te atoms, whereas the Ge(2) atom is covalently bonded with one Sb(2) and three Te atoms in a distorted tetrahedral geometry. The title compound is the first example of a chalcogenide that shows Ge-Sb bonding. The Sb(1) atom is present at the center of the seesaw geometry of four Te atoms. In contrast, the Sb(2) atom forms a seesaw geometry by coordinating with one Ge(2) and three Te atoms. Condensation of these Ge and Sb centered polyhedral units lead to the formation of ₁^∞[Ge₂Sb₂Te₁₀]^8- stripes. The temperature-dependent resistivity study suggests the semimetallic/degenerate semiconducting nature of polycrystalline Ba₄Ge₂Sb₂Te₁₀. The positive sign of Seebeck coefficient values indicates that the predominant charge carriers are holes in Ba₄Ge₂Sb₂Te₁₀. An extremely low lattice thermal conductivity of ∼0.34 W/mK at 773 K was observed for polycrystalline Ba₄Ge₂Sb₂Te₁₀, which is presumably due to the lattice anharmonicity induced by the stereochemically active 5s² lone pair of Sb. The electronic structure of Ba₄Ge₂Sb₂Te₁₀ and the bonding of atom pairs in the structure have been analyzed by means of ELF analysis and crystal orbital Hamilton population (COHP) analysis.

Ba4GeSb2Se11: An Infrared Nonlinear Optical Crystal with a V-Shaped Se32- Group Possessing a Large Contribution to the SHG Response

The quaternary selenide Ba₄GeSb₂Se₁₁ was prepared by a high-temperature solid state reaction method. Ba₄GeSb₂Se₁₁ crystallizes in an acentric orthorhombic space group Cmc2₁ with the lattice constants a = 9.370(11) Å, b = 25.850(0) Å, and c = 8.798(10) Å. The compound is composed of a [SbSe₃]^3- trigonal pyramid, [GeSbSe₅]^3- dimers, V-shaped Se₃^2-, and the adjacent Ba²⁺ ions. It has indirect band gap of 1.35 eV and exhibits a second harmonic generation intensity of about 0.2 times that of the benchmark compound AgGaS₂ at the same particle size. Interestingly, theoretical analyses show that the central Se atom of Se₃^2- has the largest contribution (8.1%) to d₃₁ compared to that of other Se atoms, which may be due to its easy swing in the a-axis direction.

Structural diversities in centrosymmetric La8S4Cl8La12S8Cl4[SbS3]8 and non-centrosymmetric Ln12S8Cl8[SbS3]4 (Ln = La and Ce): syntheses, crystal and electronic structures, and optical properties

Three thioantimonides charge compensated by Ln/S/Cl cationic layers, namely, La8S4Cl8La12S8Cl4[SbS3]8 and Ln12S8Cl8[SbS3]4 (Ln = La and Ce), have been discovered by conventional solid-state reactions. The former crystallizes in the centrosymmetric space group Pbcm (no. 57), while the latter adopts the polar non-centrosymmetric space group Cc (no. 9). Both of them contain isolated SbS3 trigonal-pyramidal units, which are connected either with the alternating centric [La8S4Cl8]8+ and mirror-symmetric [La12S8Cl4]16+ cationic layers perpendicular to the [001] direction in La8S4Cl8La12S8Cl4[SbS3]8 or with the acentric [Ln12S8Cl8]12+ cationic layers perpendicular to the [100] direction in Ln12S8Cl8[SbS3]4. Interestingly, the discrete SbS3 trigonal pyramids pack in a centrosymmetric and non-centrosymmetric fashion in La8S4Cl8La12S8Cl4[SbS3]8 and La12S8Cl8[SbS3]4, respectively, which can be ascribed to the different compositions and packing fashions in Ln/S/Cl cationic layers. In addition, optical gaps of 2.31 and 2.60 eV for La12S8Cl8[SbS3]4 and La8S4Cl8La12S8Cl4[SbS3]8, respectively, were determined by UV/vis reflectance spectroscopy, showing a blue shift with respect to La7Sb9S24, which can be attributed to the greater contributions of La to the bottom of the CB as confirmed by the DFT study.

Syntheses, structures, and properties of sulfides constructed by SbS4teeter-totter polyhedra: Ba3La4Ga2Sb2S15and BaLa3GaSb2S10

Two new pentanary sulfides Ba₃La₄Ga₂Sb₂S₁₅(1) and BaLa₃GaSb₂S₁₀(2) have been discovered.

Ba3TM2Se9 (TM = Nb, Ta): synthesis and characterization of new polyselenides

New ternary polyselenides Ba3TM2Se9 (TM = Nb, Ta) were synthesized through a solid-state reaction, and their structures were characterized using single-crystal X-ray diffraction. These compounds crystallized into a new structural type with a monoclinic space group P21/c. The structures were constructed from distorted, close-packed layers of ∞3[BaSe3]3.33– that incorporated TM atoms at octahedral sites and contained [(TM5+)2(Se2–)7(Se22–)] units. Diffuse reflectance spectra and electronic resistivity measurements indicated semiconducting properties and optical band gaps of 1.3 eV for Ba3Nb2Se9 and 1.6 eV for Ba3Ta2Se9. Raman spectra were used to investigate the interatomic interactions. Calculations of the electronic structure verified the semiconducting behavior and bonding interaction of short Se–Se contacts.