Material Descriptors to Search for Low-Temperature Thermoelectric Materials

Thermoelectric (TE) cooling offers an environmentally-friendly and reliable alternative to modern vapor compression cycles that utilize harmful refrigerants. One of the major bottlenecks in adopting TE cooling is the lack of low-temperature TE materials. In this study, we derive computationally-accessible material descriptors from a two-band Boltzmann transport model and predict the TE performance of narrow-gap semiconductors and semimetals. Through analytical modeling, we find that materials exhibiting high asymmetry between the transport distribution functions of electrons and holes yield high TE performance in narrow-gap semiconductors and semimetals. The high asymmetry manifests in the suppression of bipolar conduction. Inspired by the high TE performance of semimetallic Mg₃Bi₂-based materials near room temperature, we apply the material descriptors to search for Zintl phases with narrow and negative band gaps for low-temperature applications. By applying the material descriptors developed in this work, we screened 667 Zintl phases from the Inorganic Crystal Structure Database (ICSD) and identified few phases as promising low-temperature TE candidates. The material descriptors can be generally applied to search for other low-temperature TE materials with narrow and negative band gaps, beyond the Zintl phases considered in this study.