Understanding the electronic and phonon transport properties of thermoelectric material BiCuSeO: a first-principles study

TL;DR

This study uses first-principles calculations and Boltzmann transport theory to analyze the electronic and phonon transport properties of BiCuSeO, revealing its semiconducting nature, band structure features, and atomic dynamics relevant for thermoelectric performance.

Contribution

It provides a detailed first-principles analysis of BiCuSeO's electronic structure, phonon behavior, and transport properties, highlighting the role of Cu atom anharmonicity.

Findings

BiCuSeO is a direct band gap semiconductor (~0.8 eV).

Valley degeneracy enhances the Seebeck coefficient.

Cu atoms exhibit strong anharmonicity due to rattling behavior.

Abstract

Using first-principles pseudopotential method and Boltzmann transport theory, we give a comprehensive understanding of the electronic and phonon transport properties of thermoelectric material BiCuSeO. By choosing proper hybrid functional for the exchange-correlation energy, we find that the system is semiconducting with a direct band gap of ~0.8 eV, which is quite different from those obtained previously using standard functionals. Detailed analysis of a three-dimensional energy band structure indicates that there is a valley degeneracy of eight around the valence band maximum, which leads to a sharp density of states and is responsible for a large p-type Seebeck coefficient. Moreover, we find that the density of states effective masses are much larger and results in very low hole mobility of BiCuSeO. On the other hand, we find larger atomic displacement parameters for the Cu atoms, which indicates that the stronger anharmonicity of BiCuSeO may originate from the rattling behavior of Cu instead of previously believed Bi atoms.