Thermal conductivity and lattice dynamics of thermoelectric oxychalcogenide BiCuTeO

Recently, BiCuTeO is considered as one of the promising thermoelectric materials due to its ultra-low thermal conductivity. For this reason, the thermoelectric characteristic of this material has been studied to evaluate the lattice thermal conductivity (𝜅𝜅𝐿𝐿) from firstprinciples calculations which are based on solving linearized Boltzmann transport equations (LBTE) through the relaxation time (RTA) approximation. These calculations are used to predict the behavior of phonons in order to understand the origin of the ultralow thermal conductivity of BiCuTeO. The lattice thermal conductivity of BiCuTeO is reproduced with high accuracy. Our calculations predict that BiCuTeO announces a strong anharmonicity, which is the cause of the very low value of the thermal conductivity. This results in very high group speeds. Moreover, the calculations of the elastic properties, dielectric constants, phonon group velocities, lifetimes, and Grüneisen parameters shows that the lattice thermal conductivity exhibits an obvious anisotropy.