Low lattice thermal conductivities and good thermoelectric performance of hexagonal antiperovskites X(Ba & Sr)BiN with quartic anharmonicity.

Antiperovskites are a burgeoning class of semiconducting materials that showcase remarkable optoelectronic properties and catalytic properties. However, there has been limited research on their thermoelectric properties. Combining first-principles calculations, self-consistent phonon theory and the Boltzmann transport equation, we have discovered that the hexagonal antiperovskites X(Ba & Sr)BiN exhibit strong quartic lattice anharmonicity, where the anharmonic vibrations of the light N atoms primarily affect the lattice thermal conductivity () along the -axis direction. As a result, the lattice thermal conductivities along the ()-axis direction are low. At 300 K, the values of BaBiN and SrBiN are only 1.27 W m K and 2.24 W m K, respectively. Moreover, near the valence band maximum, the orbitals of the N atoms dominate. This dominance allows SrBiN to achieve high power factor under p-type doping, resulting in an impressive thermoelectric figure of merit () of 0.94 along the -axis direction at 800 K. In the ()-axis direction, at 800 K, n-type doped BaBiN exhibits a value of 1.47, surpassing that of traditional thermoelectric materials. Our research elucidates that the hexagonal antiperovskites X(Ba & Sr)BiN represent a category of potential thermoelectric materials with pronounced anisotropy, low thermal conductivity, and high thermoelectric performance.