Nanostructured rocksalt-type solid solution series (Ge1−xSnxTe)nSb2Te3 (n=4, 7, 12; 0≤x≤1): Thermal behavior and thermoelectric properties

Kurzfassung

Solid solutions (Ge1−xSnxTe)nSb2Te3 (n=4, 7, 12; 0≤x≤1) represent stable high-temperature phases and can be obtained as metastable compounds by quenching. High-resolution transmission electron microscopy reveals that the quenched (pseudo-)cubic materials exhibit parquet-like nanostructures comparable to, but especially for n=4 more pronounced than in (GeTe)nSb2Te3 (GST materials). The temperature-dependent phase transitions are comparable; however, substitution with Sn significantly lowers the transition temperatures between cubic high-temperature phase and the long range ordered layered phases that are stable at ambient conditions. In addition, the metrics of the quenched Sn-containing materials remains closer to cubic, especially for samples with n=7 or 12. For samples with high defect concentrations (n=4, 7), Sn-substituted samples exhibit electrical conductivities up to 3 times higher than those of corresponding GST materials. Since the difference in thermal conductivity is much less pronounced, this results in a doubling of the thermoelectric figure of merit (ZT) at high temperatures for (Ge0.5Sn0.5Te)4Sb2Te3 as compared to (GeTe)4Sb2Te3. Sn doping in (GeTe)7Sb2Te3 increases the ZT value by a factor of up to 4 which is also due to an increased Seebeck coefficient.