Novel metal oxides with promising high-temperature thermoelectric performance

Abstract

Metal oxides are particularly promising high-temperature thermoelectric (TE) materials due to their excellent high-temperature stability, eco-friendliness and cost-effectiveness. Yet, their poor TE performance has become the main bottleneck for their wide application. As a result, it is imperative to find novel oxide materials with superior thermoelectric performance for applications at high temperatures. In this work, a high-throughput (HT) materials-discovery effort has been made to discover promising TE oxides using the ALKEMIE platform. A novel type of oxide MTa₂O₆ (M = Mg, Ca) was discovered for high-temperature TE applications. In addition, another screened oxide, SrTiO₃, a well-known n-type perovskite oxide, was used as a benchmark for comparison. The calculated results indicate that CaTa₂O₆ possesses a similar band structure to SrTiO₃ and thus superior electrical-transport performance. MgTa₂O₆ exhibits a peak value of the thermoelectric figure of merit, ZT, of larger than unity at 1000 K. We find that MgTa₂O₆ has a superior Seebeck coefficient compared with SrTiO₃ or CaTa₂O₆. Further analysis of the electronic structure suggests that the flat conduction-band edge in MgTa₂O₆ produces a highly energy-dependent electronic density of states, and thus the high Seebeck coefficient. Furthermore, a significant reduction of the phonon relaxation time is the origin of the observed decrease in the calculated thermal conductivity between 300 K and 1000 K. The present work demonstrates the results of a rapid and successful HT screening of high-temperature TE materials, and can be extended to the exploration of other new materials.