Comparative first-principles study of antiperovskite oxides and nitrides as thermoelectric material: multiple Dirac cones, low-dimensional band dispersion, and high valley degeneracy
Abstract
We perform a comparative study on thermoelectric performance of antiperovskite oxides Ae3TtO and nitrides Ae3PnN (Ae= Ca, Sr, Ba; Tt= Ge, Sn, Pb; Pn= As, Sb, Bi) by means of first-principles calculation. As for the oxides with the cubic structure, Ca3GeO with a sizable band gap exhibits high thermoelectric performance at high temperatures, while Ba3PbO with Dirac cones without the gap is favorable at low temperatures. The latter high performance owes to high valley degeneracy including the multiple Dirac cones and the valleys near the and R points. For the nitrides with the cubic structure, insulator with strong quasi-one-dimensionality exhibits high thermoelectric performance. We also find that the orthorhombic structural distortion sometimes sizably enhances thermoelectric performance, especially for Ba3GeO and Sr3AsN where the high valley degeneracy is realized in the Pnma phase. Our calculation reveals that antioerpvskites offer a fertile playground of various kinds of characteristic electronic structure, which enhance the thermoelectric performance, and provides promising candidates of high-performance thermoelectric materials.