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 (Y_0.1Nd_0.1Sm_0.1Gd_0.1Dy_0.1Ho_0.1Er_0.1Tm_0.1Yb_0.1Lu_0.1)TaO₄ ((10RE_0.1)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 (10RE_0.1)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 (10RE_0.1)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, (10RE_0.1)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.

Key words: High-entropy rare-earth tantalate ceramic, Ferroelastic domain, Lattice distortion, Oxygen vacancy, Thermal conductivity, Thermal barrier coatings materials