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

ABSTRACT: 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(?,?,1/2)000(-?,?,1/2)000 (No. and Pm21n(?,?,1/2)000(-?,?,1/2)000 (No., with modulation wave vectors q1 = ?a* + ?b* + 1/2c* and q2 = -?a* + ?b* + 1/2c* [? = 0.272?(1) and ? = 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.


PROVIDER: S-EPMC7273186 | BioStudies | 2020-01-01

REPOSITORIES: biostudies

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