# Comparative first-principles study of antiperovskite oxides and nitrides as thermoelectric material: multiple Dirac cones, low-dimensional band dispersion, and high valley degeneracy

## TL;DR

This study uses first-principles calculations to compare thermoelectric properties of antiperovskite oxides and nitrides, revealing how structural and electronic features like Dirac cones and valley degeneracy influence performance.

## Contribution

It identifies specific antiperovskite compounds with high thermoelectric efficiency due to unique electronic structures and structural distortions, expanding potential material candidates.

## Key findings

- Ca3GeO has high performance at high temperatures due to its band gap.
- Ba3PbO exhibits high performance at low temperatures with Dirac cones.
- Orthorhombic distortion can enhance thermoelectric performance.

## Abstract

We perform a comparative study on thermoelectric performance of antiperovskite oxides $Ae_3Tt$O and nitrides $Ae_3Pn$N ($Ae=$ 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, Ca$_3$GeO with a sizable band gap exhibits high thermoelectric performance at high temperatures, while Ba$_3$PbO 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 $\Gamma$ 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 Ba$_3$GeO and Sr$_3$AsN 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.