High-entropy ferroelastic (10RE0.1)TaO4 ceramics with oxygen vacancies and improved thermophysical properties

Abstract

The primary purpose of this work is to optimize the thermophysical properties of rare-earth tantalate ceramics using the high-entropy effect. Here, the high-entropy rare-earth tantalate ceramic (Y0.1Nd0.1Sm0.1Gd0.1Dy0.1Ho0.1Er0.1Tm0.1Yb0.1Lu0.1)TaO4 ((10RE0.1)TaO4) is synthesized successfully. The lattice distortion and oxygen vacancy concentration are characterized firstly in the rare-earth tantalates. Notably, compared with single rare-earth tantalates, the thermal conductivity of (10RE0.1)TaO4 is reduced by 16%–45% at 100 °C and 22%–45% at 800 °C, and it also presents lower phonon thermal conductivity in the entire temperature range from 100 to 1200 °C. The phonon thermal conductivity (1.0–2.2 W m−1 K−1, 100–1200 °C) of (10RE0.1)TaO4 is lower than that of the currently reported high-entropy four-, five- and six-component rare-earth tantalates. This is the result of scattering by the ferroelastic domain, lattice distortion associated with size and mass disorder, and point defects, which target low-, mid- and high-frequency phonons. Furthermore, (10RE0.1)TaO4, as an improved candidate for thermal barrier coatings materials (TBCs), has a higher thermal expansion coefficient (10.5×10−6 K−1 at 1400 °C), lower Young's modulus (123 GPa) and better high-temperature phase stability than that of single rare-earth tantalates.