High temperature neutron powder diffraction study of the Cu12Sb4S13 and Cu4Sn7S16 phases

Abstract : Ternary copper-contg. sulfides Cu12Sb4S13 and Cu4Sn7S16 have attracted considerable interest since few years due to their high-efficiency conversion as absorbers for solar energy and promising thermoelec. materials. We report therein on the decompn. study of Cu12Sb4S13 and Cu4Sn7S16 phases using high temp. in situ neutron powder diffraction. Our results obtained at a heating rate of 2.5 K/min indicate that: (i) Cu12Sb4S13 decomps. above ≈792 K into Cu3SbS3, and (ii) Cu4Sn7S16 decomps. above ≈891 K into Sn2S3 and a copper-rich sulfide phase of sphalerite ZnS-type structure with an assumed Cu3SnS4 stoichiometry. Both phase decompns. are assocd. to a sulfur volatilization. While the results on Cu12Sb4S13 are in fair agreement with recent published data, the decompn. behavior of Cu4Sn7S16 differs from other studies in terms of decompn. temp., thermal stability and products of reaction. Finally, the crystal structure refinements from neutron powder diffraction data are reported and discussed for the Cu4Sn7S16 and tetrahedrite Cu12Sb4S13 phases at 300 K, and for the high temp. form of skinnerite Cu3SbS3 at 843 K.