Low lattice thermal conductivity in arc-melted GeTe with Ge-deficient crystal structure

GeTe is a well-known thermoelectric material, with transport properties strongly dependent on the composition and crystal structure. Phase-pure polycrystalline GeTe has been prepared by a straightforward arc-melting technique, and its structural and physical properties are studied by neutron powder diffraction (NPD), electron microscopy, calorimetry, and transport measurements. The structural analysis from NPD data reveals a conspicuous Ge deficiency in the bulk structure (similar to 7% atomic vacancies), confirmed by the Hall-carrier concentration. The analysis of the atomic displacement parameters shows strong anisotropy of Ge ellipsoids, revealing a considerable anharmonicity of the chemical bonds. Concerning the thermoelectric properties, the samples display high electrical conductivity and reduced lattice contribution to the total thermal conductivity, exhibiting record-low 0.8 W m(-1) K-1 at 770 K, as a consequence of the highly defective crystal structure. Both are essential ingredients of useful thermoelectric materials, indicating the applicability of defective GeTe in polycrystalline form. Published by AIP Publishing.