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

Rare-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)(3)TaO7, (Nd0.2Sm0.2Eu0.2Gd0.2Tm0.2)(3)TaO7, and (Ce0.2Nd0.2Sm0.2Eu0.2Dy0.2)(3)TaO7, 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<middle dot>K)(-1) at 1000 degrees 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 x 10(-6) K-1 at 1200 degrees 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.