Ab initio dynamical stability and lattice thermal conductivity of vanadium and niobium at high temperature

Abstract

It is believed that the quasi-harmonic approximation can well describe the volume-dependent phonon frequency of most materials at zero temperature. In this work, we found that this widely used method cannot accurately describe the phonon frequencies of transition metals V and Nb at 0 GPa and 0 K. Therefore, the phonon-phonon interactions are further considered, and the phonon dispersion curves of V and Nb varying with temperature under zero pressure are derived. It is found that the calculated phonon dispersion curves of them at 300 K are in good agreement with the experimental results, indicating that the anharmonic effect is of great importance in the case of V and Nb. In addition, combined with the Boltzmann transport equation of phonons, the lattice thermal conductivity of V and Nb is also studied. The results show that the lattice thermal conductivity of V and Nb at 300 K is 4.35 and 9.87 Wm−1K−1, which are far lower than their electronic thermal conductivity at the same temperature, indicating that the electronic thermal conductivity of V and Nb is dominant at room temperature.