Crystal structure, microstructure, and thermoelectric properties of GeSb6Te10 prepared by spark plasma sintering

We report the effects of spark plasma sintering (SPS) and subsequent annealing on the crystal structure, microstructure, and thermoelectric properties of polycrystalline GeSb6Te10. GeSb6Te10 consolidated using SPS consisted of a mixture of GeSb6Te10-type homologous and Sb2Te3-type tetradymite structures, whereas the sample prepared by melting had a single homologous structure. SPS produced small amounts of Ge-rich precipitates with a few micrometers in size. Even excluding these precipitates, the elemental compositional deviation from the nominal composition was wider than that for the sample prepared by melting. This implies that SPS promoted atomic diffusion and rearrangement of elements, leading to a substantial change in the crystal structure and elemental distribution of GeSb6Te10. SPS improved the power factor but also increased the thermal conductivity, as a result of the increased electrical conductivity, yielding a maximum dimensionless figure of merit, ZTmax, of 0.33 at 710 K, which is similar to the value for the sample prepared by melting (0.39 at 710 K).