Single crystal structure elucidation and thermoelectric properties of a long-periodically ordered germanium arsenic telluride

Abstract Single-crystal X-ray diffraction revealed that the structure of As 2 Ge 7 Te 10  = (GeTe) 7 As 2 Te 3 (space group  R 3 ¯ m ) consists of rocksalt-type building blocks separated by van der Waals gaps. As and Ge are disordered on some of the cation sites. The rhombohedral 57 R stacking sequence results in an extraordinarily large lattice parameter of c  = 103.41 (2) A. When such structures are formed, the extremely long diffusion pathways required to obtain completely ordered compounds often lead to samples that contain intergrown rocksalt-type slabs with varying thicknesses. As a result, the system (GeTe) n As 2 Te 3 is prone to form both disordered and inhomogeneous samples, expecially for n > 9. Yet, powder diffraction data reveal that such samples contain 57 R -As 2 Ge 7 Te 10 as a main component. Such inhomogeneous materials exhibit promising thermoelectric properties: the Seebeck coefficient as well as the lattice part of the thermal conductivity are in the same range as germanium antimony tellurides with high figures of merit ZT . However, the high electrical conductivity and consequently the rather dominant electronic component of thermal transport still impede such ZT values for germanium arsenic tellurides.