A Phonon-Unfolding Based Method for Quantitative Assessment of Thermal Conductivity of High Entropy Ceramics

Thermal barrier coating materials have been extensively used in fields of aerospace and power industry. It can protect the underlying substrate against hot gas streams while effectively isolating the heat flow. High entropy ceramics, with their unique disorder lattice structures, exhibit ultra-low thermal conductivity and good high temperature stability, which make them promising candidate materials for next generation thermal barrier coatings (TBCs). Unlike the conventional ceramic materials where the intrinsic thermal resistance largely comes from phonon-phonon interactions, the thermal resistance in high entropy ceramics predominantly arises from phonon-disorder scattering. In this study, we propose a new method based on the supercell phonon unfolding (SPU) technique to predictively assess the thermal conductivity of high entropy ceramics, focusing on the high entropy rocksalt oxide group as the representation. We demonstrated that our method could obtain an indicator in direct correspondence to the thermal conductivity, thus allowing quantitative comparison of the thermal conductivities of different high entropy ceramics. A good agreement has been found between our model predictions and the experimental measurements, confirming the validity of our method. The method provides a valuable predictive tool for screening and design of high entropy ceramics for TBCs.