First-principles study of the temperature-induced band renormalization in thermoelectric filled skutterudites.

Band structure characteristics, such as band gap and band dispersion, are fundamental properties of materials. Temperature can affect them because of lattice expansion and phonon-induced atomic vibrations. Here, we apply the recently developed electron-phonon renormalization method to study the temperature effect on the band structures of thermoelectric (TE) filled skutterudites BaCoSb, BaFeSb, and YbFeSb from first-principles. The results reveal that the band gap in BaCoSb drops slower with temperature compared with our previous study on CoSb, where it considerably reduces from 0 K to 800 K for BaFeSb (∼0.222 eV) and YbFeSb (∼0.201 eV). Furthermore, the band dispersions near the band edges at the -point in the three systems at high temperatures are similar to those at 0 K, and the electron energies have small linewidths, whereas the linewidths for energies near the Fermi level are large. The different phenomena are due to the different phonon vibration-induced electronic structure disorders, reflecting the strength of electron-phonon coupling. Band renormalization would further affect the TE properties of these filled skutterudites. Our work provides a deeper understanding of the temperature-dependent band structure in skutterudites.