Crystal structure determination of CoGeTe from powder diffraction data

Abstract

The crystal structure of cobalt germanium telluride CoGeTe has been determined by direct methods using integrate intensities of conventional X-ray powder diffraction data and subsequently refined with the Rietveld method. The title compound was prepared by heating of stoichiometric amount of Co, Ge and Te in silica glass tube at 670 °C. CoGeTe adopts orthorhombic symmetry, space group Pbca with unit cell parameters a = 6.1892(4) Å, b = 6.2285(4) Å, c = 11.1240(6) Å, V = 428.8(1) Å 3 and Z = 8. Its crystal structure is formed by [CoGe 3Te 3] octahedra sharing both edges and corners. CoGeTe represents a ternary ordered variant of α-NiAs 2 type structure. An important feature present in CoGeTe is an occurrence of short Co–Co distance across the shared edge of [CoGe 3Te 3] octahedra. Differential thermal analysis (DTA) has revealed that CoGeTe melts incongruently at about 725 °C; CoGeTe decomposes into GeTe, CoGe and CoTe 2. Temperature dependence of the electrical conductivity and value of Seebeck coefficient at 300 K are also reported.