Thermoelectric Borides: Review and Future Perspectives

Abstract

The conversion of waste heat into electricity plays a vital role in energy harvesting since conventional non‐renewable energy sources have been rapidly approaching the limit of utilization. The thermoelectric (TE) technology relies on converting temperature difference (or waste heat) into electricity or vice versa. The performance of TE materials is gauged by zT = S 2 T /ρκ, where  S , ρ , κ , and T represent the Seebeck coefficient, the electrical resistivity, the total thermal conductivity, and the absolute temperature, respectively. Boron‐based compounds are considered refractory materials due to their high melting points and advanced chemical and mechanical stability. Besides high thermal stability, many borides exhibit intrinsically low thermal conductivity. The discovery of good TE efficiency in boron carbides, where unexpectedly high Seebeck coefficients ( S ( T ) ≈ 250 µVK −1 ) are observed at high charge carrier densities (≈10 21 cm −3 ), has induced an intense curiosity for the TE properties of other boron‐based compounds. Intermetallic borides with high boron content (>65 at%) are of particular interest among all known TE materials due to their great potential in TE generators, which can operate under extreme environmental conditions ( T > 1000 K). This article reviews the TE properties of borides and state‐of‐art TE materials upon boron/borides doping.