LaTe1.9: a tenfold superstructure of the ZrSSi type.

Single crystals of LaTe1.9 (lanthanum telluride) have been obtained by chemical transport reactions with iodine as transport agent. LaTe1.9 adopts the CeSe1.9 structure type and crystallizes in the space group P42/n with lattice parameters a = 10.1072 (3) Šand c = 18.2874 (6) Å. The crystal structure comprises an alternating stacking of puckered [LaTe] slabs and planar [Te] layers along [001]. The planar [Te] layer is dominated by dumbbell-shaped Te2 2- anions along an isolated Te2- anion and a vacancy. The Te2 2- anions form an eight-membered ring enclosing the vacancy in the centre.

Synthesis, structure, electronic and thermal properties of sphalerite CuZn2InS4.

Quaternary chalcogenides continue to be of interest due to the variety of physical properties they possess, as well as their potential for different applications of interest. Investigations on materials with the sphalerite crystal structure have only recently begun. In this study we have synthesized sulfur-based sphalerite quaternary chalcogenides, including off-stoichiometric compositions, and investigated the temperature-dependent electronic, thermal and structural properties of these materials. Insulating to semiconducting transport is observed with stoichiometric variation, and analyses of heat capacity and thermal expansion revealed lattice anharmonicity that contributes to the low thermal conductivity these materials possess. We include similar analyses for CuZn2InSe4 and compare these sphalerite quaternary chalcogenides to that of zinc blende binaries in order to fully understand the origin of the low thermal conductivity these quaternary chalcogenides possess.

Structural Variations and Bonding Analysis of the Rare-Earth Metal Tellurides RETe1.875±Î´ (RE = Ce, Pr, Sm, Gd; 0.004 ≤ δ ≤ 0.025).

Crystals of RETe1.875±Î´ (RE = Ce, Pr, Sm, Gd; 0.004 ≤ δ ≤ 0.025) were grown using alkali halide flux and chemical transport reactions. The crystal structures are described in space group Amm2 (no. 38), with lattice parameters of a = 13.3729(5) Å, b = 17.7918(5) Å, c = 18.1561(4) Å for CeTe1.87(1) (T = 100 K), a = 13.271(2) Å, b = 17.747(3) Å, c = 18.160(3) Å for PrTe1.85(1) (T = 100 K), a = 13.1251(6) Å, b = 17.4269(8) Å, c = 17.8808(8) Å for SmTe1.87(1) (T = 100 K), and a = 13.1762(4) Å, b = 17.4995(5) Å, c = 17.9591(5) Å for GdTe1.88(1) (T = 296 K). The structures contain alternating stacks of puckered [RETe] slabs and planar [Te] layers. The latter are composed of small anionic entities, such as Te2- and Te22-, along with a large anionic eight-membered Te ring, as supported by electron localizability indicator-based bond analysis for an ordered model of GdTe1.875. Slightly different patterns for individual compounds indicate a considerable structural flexibility. Temperature-dependent resistance measurements confirm semiconducting behavior for PrTe1.875±Î´ and GdTe1.875±Î´ (magnetic data evidence RE3+ and an antiferromagnetic transition at TN = 4 K for CeTe1.875±Î´ and TN = 11 K for GdTe1.875±Î´), whereas PrTe1.875±Î´ and SmTe1.875±Î´ show no long-range order down to 2 K.

Distorted Te nets in the modulated crystal structures of RETe1.94(1) (RE = La, Pr, Nd).

The two-dimensionally incommensurately modulated crystal structures of the compounds RETe1.94(1) (RE = La, Pr, Nd) were investigated by single-crystal X-ray diffraction. The compounds crystallize in the tetragonal superspace group P4/n(αß½)00(-ßα½)00 (No. 85.2.58.2) with q1 = αa*+ßb*+½c* and q2 = -ßa*+αb*+½c* and share a common motif of an alternating stacking of a puckered [RETe] layer and a planar [Te] layer. This basic structural motif is observed for all reported compounds with unusually large anisotropic displacement parameters in the planar [Te] layer. Taking the modulation into account, a distortion from this perfect square planar net is noted along with vacancies in the planar [Te] layer. The distortion leads to the formation of different discrete anions, like Te2-, Te22- and Te32-, similar to previously reported structures for REX2-δ compounds (RE = trivalent rare earth metal, X = S, Se, Te). The Te-Te distances in the modulated [Te] layer are found in a narrow range as compared to those in the corresponding sulfides and selenides.

LaTe1.82(1): modulated crystal structure and chemical bonding of a chalcogen-deficient rare earth metal polytelluride.

Crystals of the rare earth metal polytelluride LaTe1.82(1), namely, lanthanum telluride (1/1.8), have been grown by molten alkali halide flux reactions and vapour-assisted crystallization with iodine. The two-dimensionally incommensurately modulated crystal structure has been investigated by X-ray diffraction experiments. In contrast to the tetragonal average structure with unit-cell dimensions of a = 4.4996 (5) and c = 9.179 (1) Šat 296 (1) K, which was solved and refined in the space group P4/nmm (No. 129), the satellite reflections are not compatible with a tetragonal symmetry but enforce a symmetry reduction. Possible space groups have been derived by group-subgroup relationships and by consideration of previous reports on similar rare earth metal polychalcogenide structures. Two structural models in the orthorhombic superspace group, i.e. Pmmn(α,ß,1/2)000(-α,ß,1/2)000 (No. 59.2.51.39) and Pm21n(α,ß,1/2)000(-α,ß,1/2)000 (No. 31.2.51.35), with modulation wave vectors q1 = αa* + ßb* + 1/2c* and q2 = -αa* + ßb* + 1/2c* [α = 0.272 (1) and ß = 0.314 (1)], have been established and evaluated against each other. The modulation describes the distribution of defects in the planar [Te] layer, coupled to a displacive modulation due to the formation of different Te anions. The bonding situation in the planar [Te] layer and the different Te anion species have been investigated by density functional theory (DFT) methods and an electron localizability indicator (ELI-D)-based bonding analysis on three different approximants. The temperature-dependent electrical resistance revealed a semiconducting behaviour with an estimated band gap of 0.17 eV.

Structural, Electronic, and Thermal Properties of CdSnAs2.

Structural, electrical, and thermal properties of CdSnAs2, with analyses from temperature-dependent transport properties over a large temperature range, are reported. Phase-pure microcrystalline powders were synthesized that were subsequently densified to a high-density homogeneous polycrystalline specimen for this study. Temperature-dependent transport indicates n-type semiconducting behavior with a very high and nearly temperature independent mobility over the entire measured temperature range, attributed to the very small electron effective mass of this material. The Debye model was successfully applied to model the thermal conductivity and specific heat. This work contributes to the fundamental understanding of this material, providing further insight and allowing for investigations into altering this and related physical properties of these materials for technological applications.