Single crystals of the polytellurides RETe1.8 of gadolinium, terbium, and dysprosium were prepared by chemical vapor transport and alkali metal halide flux reactions. To determine proper synthesis conditions for the desired target composition, the binary phase diagram Gd‐Te was evaluated by CalPhaD methods. The compounds are isostructural to SmTe1.8 and crystallize in space group P4/n (no. 85) with lattice parameters of a = 966.10(4), 960.00(3), and 957.33(2) pm and c = 1794.15(10), 1785.77(6), and 1779.38(5) pm for GdTe1.8, TbTe1.8 and DyTe1.8, respectively. The structures consist of puckered [RETe] double slabs and planar telluride layers composed of Te2 dumbbells and linear Te3 units in accordance with ELI‐D based bonding analyses. The latter can be understood as a Te34– anion. GdTe1.8 is a semiconductor with a bandgap of 0.19 eV/0.17 eV (experimental/calculated). Magnetization data confirm trivalent RE ions and indicate antiferromagnetic order at TN = 12 K for TbTe1.8 and TN = 9.8 K for DyTe1.8, whereas GdTe1.8 remains paramagnetic down to 2 K.
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) Å at 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,β,)000(−α,β,)000 (No. 59.2.51.39) and Pm21n(α,β,)000(−α,β,)000 (No. 31.2.51.35), with modulation wave vectors q1 = αa* + βb* + c* and q2 = −αa* + βb* + c* [α = 0.272 (1) and β = 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.
Crystals of RETe 1.875±δ (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,
A new calcium iron ruthenium hydrogarnet with the approximate composition Ca3(Ru2−xFex)(FeO4)2−y(H4O4)1+y (x=1, y≈0.35) has been obtained by hydrothermal synthesis under oxidizing alkaline conditions. The compound crystallizes in the cubic space group Ia3̅d (No. 230) with a lattice parameter of a=12.4804(4) Å (T=100 K) and Z=8. The octahedral site of the garnet structure is equally occupied by Ru and Fe, whereas the tetrahedral site is partially occupied by Fe only. A partial substitution of the oxide anions by hydroxide ions is necessary for charge balancing, corresponding to the so-called hydrogarnet defects. The presence of hydroxide groups is proven by infrared spectroscopy. 57Fe Mössbauer spectroscopic data provide evidence for two different Fe3+ coordination environments as well as a magnetic ordering of two iron substructures with the respective ordering temperature above room temperature. The crystal composition was verified by energy-dispersive X-ray spectroscopy and the thermal behavior of the calcium iron ruthenate was studied by difference thermal analysis.
Structural, electrical, and thermal properties of CdSnAs 2 , 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.
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