A synchrotronpowder X-ray diffraction study of the skutterudite-related phases AB1.5Te1.5 (A = Co, Rh, Ir; B = Ge, Sn)

Abstract

X-Ray resonant scattering has been exploited to investigate the crystal structure of the AB_1.5Te_1.5 phases (A = Co, Rh, Ir; B = Ge, Sn). Analysis of the diffraction data reveals that CoGe_1.5Te_1.5 and ASn_1.5Te_1.5 adopt a rhombohedral skutterudite-related structure, containing diamond-shape B₂Te₂ rings, in which the B and Te atoms are ordered and trans to each other. Anion ordering is however incomplete, and with increasing the size of both cations and anions, the degree of anion ordering decreases. By contrast, the diffraction data of IrGe_1.5Te_1.5 are consistent with an almost statistical distribution of the anions over the available sites, although some ordered domains may be present. The thermoelectric properties of these materials are discussed in light of these results.