Origins of the high temperature increase of the thermal conductivity of transition metal carbides from atomistic simulations

Abstract

To understand the unexpected increase of the thermal conductivity of transition metal carbides at high temperatures, we calculate, with atomistic simulations, the thermal conductivity of zirconium carbide (ZrC). To account for the common substoichiometry of this material, various numbers of carbon vacancies are considered. The vibrational part of the conductivity is calculated by empirical potential molecular dynamics while the electronic part is calculated from density functional theory electronic structure with the Kubo–Greenwood formula on selected atomic configurations generated by the same empirical potential. We find that the vibrational part of the conductivity is negligible at temperatures higher than 1500 K. The increase of thermal conductivity with temperature is quantitatively reproduced in the calculations. It appears for all compositions and proves to rely entirely on its electronic component. Three phenomena are found responsible for the rise of the thermal conductivity with temperature: the semi-metallic shape of the electronic density of states, the additional electrical resistivity induced by carbon vacancies and the rise of the density of states with either temperature or the concentration of vacancies.