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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) Å and 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.

Crystals of RETe1.875±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) A, b = 17.7918(5) A, c = 18.1561(4) A for CeTe1.87(1) (T = 100 K), a = 13.271(2) A, b = 17.747(3) A, c = 18.160(3) A for PrTe1.85(1) (T = 100 K), a = 13.1251(6) A, b = 17.4269(8) A, c = 17.8808(8) A for SmTe1.87(1) (T = 100 K), and a = 13.1762(4) A, b = 17.4995(5) A, c = 17.9591(5) A 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±δ and GdTe1.875±δ (magnetic data evidence RE3+ and an antiferromagnetic transition at TN = 4 K for CeTe1.875±δ and TN = 11 K for GdTe1.875±δ), whereas PrTe1.875±δ and SmTe1.875±δ show no long-range order down to 2 K.

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.

The two-dimensionally incommensurately modulated crystal structures of the compoundsRETe1.94(1)(RE= La, Pr, Nd) were investigated by single-crystal X-ray diffraction. The compounds crystallize in the tetragonal superspace groupP4/n(αβ½)00(−βα½)00 (No. 85.2.58.2) withq1= αa*+βb*+½c* andq2= −βa*+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 forREX2–δcompounds (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.

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 ofa= 4.4996 (5) andc= 9.179 (1) Å at 296 (1) K, which was solved and refined in the space groupP4/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,1 \over 2)000(−α,β,1 \over 2)000 (No. 59.2.51.39) andPm21n(α,β,1 \over 2)000(−α,β,1 \over 2)000 (No. 31.2.51.35), with modulation wave vectorsq1 = αa* + βb* + 1 \over 2c* andq2= −αa* + βb* + 1 \over 2c* [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.

Single crystals of LaTe

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 CuZn

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.

Crystals of

Magnetic topological semimetals (MTSs) are quantum materials highly desirable for spintronics. We report the synthesis, the crystal structure, the chemical bonding analysis, the magneto(transport) properties, and the bulk and surface electronic structures of GdBiTe. It is a high-Z isostructural analogue of the archetypical nodal-line TS ZrSiS and a recently discovered MTS LnSbTe (Ln = Ce, Gd). GdBiTe crystallizes in the nonsymmorphic space group P4/nmm (No. 129) with a = 4.3706(2) Å and c = 9.2475(7) Å. Chemical bonding analysis describes it as a layered structure of alternating weakly bonded double-stacked covalent [GdTe] layers and planar square [Bi] nets. GdBiTe exhibits an antiferromagnetic transition at TN = 15 K, and an additional transition, possibly a spin reorientation into a canted antiferromagnetic state, occurs below ca. 5 K. The electrical resistivity is compatible with a semimetallic behavior above TN.

The two-dimensionally incommensurately modulated crystal structures of the compounds RETe

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 Te3(4–) 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 T(N) = 12 K for TbTe1.8 and T(N) = 9.8 K for DyTe1.8, whereas GdTe1.8 remains paramagnetic down to 2 K.

A new calcium iron ruthenium hydrogarnet with the approximate composition Ca3(Ru2− x Fe x )(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

The synthesis, structure, and temperature dependent thermal and electrical properties of off-stoichiometric polycrystalline modified zinc blende quaternary chalcogenides Cu1.33+xZn1.33-xIn1.33Se4, where x ​= ​0, 0.1, 0.2 and 0.3, are investigated. Temperature-dependent electrical properties reveal these compositions to be semiconductors with alteration of the carrier concentration and electrical transport via stoichiometric variation. The thermal conductivity is low for all specimens and intrinsic to these materials. First principles calculations are also reported in establishing a fundamental investigation that illustrates the large variation in stoichiometry that is possible in these materials. This stoichiometric variation results in the observed variation of the transport properties. The results presented reveal fundamental structure-property relationships in these quaternary chalcogenides, and provides a basis for further research into the viability for large stoichiometric variation in other materials that are of interest for technological applications.

The chemistry of new materials and the effects of chemical substitutions on physical properties continues to be of intense interest as it directly affects many technological fields. The synthesis and temperature dependent transport properties of GdTe1.62Se0.18 were investigated revealing polaronic transport upon simple alloying with selenium. Temperature-dependent resistivity and thermopower measurements indicate strong electron-phonon coupling, as compared to the few other chalcogenides that display such transport. In addition, the low thermal conductivity is intrinsic for this material, and a result of the stacking arrangement in the crystal structure as well as of a statistical disordered Te22– anion.

Three hexasodium transition metal sulfates, Na6M(SO4)4·2H2O (M = Fe, Co, Ni) were obtained by a dissolution and precipitation route and by hydrothermal reactions. The compounds were characterized by single crystal X-ray diffractions, UV/vis and IR spectroscopy, thermal analyses, and magnetization measurements. The title compounds all crystallize in the triclinic space group P 1 ‾ (No. 2) with Z = 1 and lattice parameters: a = 6.0679(8), b = 6.8658(8), c = 10.1508(12) A, β = 92.557(4)° for Na6Fe(SO4)4·2H2O; a = 6.0595(5), b = 6.8446(6), c = 10.1149(8), β = 92.548(2)° for Na6Co(SO4)4·2H2O; a = 6.0490(4), b = 6.8265(5), c = 10.0793(7), β = 92.5470(10)° for Na6Ni(SO4)4·2H2O, respectively. [M(SO4)4]6- anions are interconnected by hydrogen bonds to form two-dimensional layers in these structures. The solid-state UV/vis/NIR diffuse reflectance spectroscopy indicates that Na6M(SO4)4·2H2O (M = Co, Ni) are insulators. Magnetization experiments show a nearly linear temperature dependence of the inverse susceptibility down to 2 K, which indicates a paramagnetic behavior for all three compounds.