Thermodynamic properties of rare‐earth tantalates enhanced by high entropy design

Abstract

AbstractRare‐earth tantalates present promise as thermal barrier coatings due to their favorable thermodynamic characteristics. To further diminish thermal conductivity, three high‐entropy tantalate samples, namely (Ce0.2Nd0.2Sm0.2Eu0.2Lu0.2)3TaO7, (Nd0.2Sm0.2Eu0.2Gd0.2Tm0.2)3TaO7, and (Ce0.2Nd0.2Sm0.2Eu0.2Dy0.2)3TaO7, denoted as HE‐1, HE‐2, and HE‐3, respectively, were synthesized in this investigation. HE‐1 exhibits a low thermal conductivity of 1.46 W/(m·K)–1 at 1000°C. The rationale behind this reduced thermal conductivity is expounded via the phonon scattering mechanism. The introduction of atomic disparities and grain size inhomogeneity, attributable to high‐entropy doping, collaborates to enhance phonon scattering, culminating in the lowest thermal conductivity. HE‐3, on the other hand, possesses a notable thermal expansion coefficient of 11.6 × 10−6 K−1 at 1200°C and manifests pronounced anisotropy in CTEs. All three high‐entropy samples demonstrate commendable mechanical properties, with Young's modulus lower than that of single‐component rare‐earth tantalates, while simultaneously exhibiting high hardness values (>8.4 GPa). This work furnishes a valuable reference for the utilization of high entropy rare‐earth tantalates in the realm of thermal barrier coatings.