Theoretical Study of Low Lattice Thermal Conductivity Induced by Antibonding and Acoustic–Optical Coupling in Nanolayered NdAgTeO Thermoelectric Material with High ZT

Abstract

The crystal structure, electronic properties, phonon transport, and thermoelectric (TE) properties of nanolayered NdAgTeO compound are assessed by utilizing the first-principles calculations and Boltzmann transport theory in the current work. Nanolayered NdAgTeO compound is a direct-bandgap semiconductor (1.30 eV) using the Perdew–Burke–Ernzerhof (PBE) functional in connection with the spin–orbit coupling (SOC) effect. The elastic modulus, ab initio molecular dynamics (AIMD) simulations, and phonon dispersion analysis confirm the high mechanical, thermal, and dynamic stabilities of the NdAgTeO compound. Due to the unique nanolayered structure, a significant anisotropy is discovered for the electronic and thermal transport properties of the NdAgTeO compound, and the multivalley properties in the conduction bands facilitate the decoupling between Seebeck coefficient and electrical conductivity. The antibonding state around the Fermi level and the strong acoustic–optical coupling within the low-frequency region favor the pronounced anharmonicity in the NdAgTeO compound, leading to the anisotropic lattice thermal conductivities of 2.76 and 0.76 W/mK in the directions of a- and c-axis, respectively, at 300 K. The electron–phonon decoupling contributes to the excellent TE properties of n-type NdAgTeO compound, which demonstrates large Seebeck coefficient and electrical conductivity, and ultimately culminating high power factor. Consequently, the optimal ZTs for n- and p-type NdAgTeO compounds reach 2.08 and 1.16 at 700 K, respectively, while in the directions of the a- and c-axis, the ZTs achieve 1.38 and 4.68 at equivalent temperature. The study not only offers profound discernment into the thermal and electronic transport characteristics of the NdAgTeO compound but also emphasizes the promising potential of nanolayered oxychalcogenide materials for TE applications.