Antibonding Cu (d)–Te (p) states and bonding inhomogeneity in inducing low lattice thermal conductivity and extraordinary thermoelectric properties of the layered heteroanionic NdCuOTe material: a first-principles study

Abstract

The crystal structure, phonon, electronic transport, and thermoelectric (TE) properties of the layered NdCuOTe material are comprehensively evaluated using first-principles calculations and Boltzmann transport theory. The NdCuOTe material is an indirect bandgap semiconductor, with a bandgap of 2.22 eV using the Heyd–Scuseria–Ernzerhof (HSE06) functional. Due to the weak interlayer interaction and strong ionic–covalent mixed bonds, the layered NdCuOTe material displays a significant bonding inhomogeneity, which is beneficial for inhibiting phonon transport. The weak bonding and heavy atomic mass of the Nd atom soften the phonon modes, which reduce the phonon group velocity and Debye temperature. The antibonding states, primarily contributed by the hybridisation of Cu 3d and Te 5p orbitals and the low-frequency rattling-like vibration of the Cu atom, lead to a strong anharmonicity. Consequently, a low lattice thermal conductivity of 1.69 W m⁻¹ K⁻¹@300 K is discovered for the layered NdCuOTe material. Futhermore, the multi-valley characteristics and the substantial mass of the Nd atom result in the degeneracy in the conduction bands, consequently leading to high Seebeck coefficients and high power factors. Additionally, the electronic transport and TE properties of the NdCuOTe material are evaluated in consideration of multiple carrier scattering rates, and the optimal figure-of-merits (ZT) for the n-type and p-type NdCuOTe materials are 2.71 and 1.69 at 900 K, respectively. Our current work not only provides the fundamental insights into the thermal and electronic transport properties of the layered NdCuOTe material, but also aids in the fabrication of high-performance thermoelectrics based on layered heteroanionic materials.