Multiscale defect-mediated thermophysical properties of high-entropy ferroelastic rare-earth tantalates

Abstract

The foremost objective of this work is to employ an entropy strategy to optimize the thermophysical properties of rare-earth (RE) tantalates. The stabilizing single-phase structure of seven-component rare-earth tantalates is verified by density functional theory calculations, and entropy-stabilized (7RE1/7)TaO4 with a defective structure is successfully synthesized via spark plasma sintering. (7RE1/7)TaO4 exhibits lower intrinsic thermal conductivity over the entire temperature range from 100 to 1200 °C. Furthermore, its intrinsic thermal conductivity (0.83–0.90 W m−1·K−1) is 39–51% and 68–71% lower compared to those of single-RE RETaO4 and 8YSZ at 1200 °C, respectively, and is even close to the limited thermal conductivity from the Cahill model. This is the result of multiscale phonon scattering by Umklapp phonon-phonon, point defect, dislocation, ferroelastic domain and distorted structures. Moreover, (7RE1/7)TaO4 exhibits superior high-temperature phase stability and excellent mechanical properties. Therefore, entropy-stabilized (7RE1/7)TaO4 compounds with ultralow thermal conductivity can be used as promising thermal insulating materials.