Phase Stability, Crystal Structure, and Thermoelectric Properties of Cu12Sb4S13-xSex Sex Solid Solutions

The solubility of selenium on the sulfur site in tetrahedrite Cu12Sb4S13 has been investigated by theoretical calculations, and the results have been verified by X-ray diffraction and X-ray synchrotron studies on Cu12Sb4S13-xSex with x ranging from zero to 3. Density-functional theory calculations predict that Se substitution on the tetrahedral 24g site is preferred, and this is found to be consistent with Rietveld refinement of the crystal structure. High temperature thermoelectric property measurements on Cu12Sb4S13-xSex reveal that Se substitution results in a decrease in electrical resistivity without diminution of the Seebeck coefficient. The decoupling of these parameters leads to a 30% enhancement in power factor of the x = 1 sample compared to that of pure Cu12Sb4S13-xSex. In addition, in spite of an-increased electronic thermal conductivity, alloy scattering of phonons caused by Se substitution reduces both the 'lattice and total thermal conductivities, leading to a large increase in the thermoelectric figure of merit.