High‐entropy ferroelastic rare‐earth tantalite ceramic: (Y 0.2 Ce 0.2 Sm 0.2 Gd 0.2 Dy 0.2 )TaO ₄

In this study, high‐entropy rare‐earth tantalate ceramics (Y 0.2 Ce 0.2 Sm 0.2 Gd 0.2 Dy 0.2 )TaO 4 ((5RE 0.2 )TaO 4 ) have been successfully fabricated. The possibility of formation of (5RE 0.2 )TaO 4 was verified via first‐principles calculations. In addition, the phase structure, ferroelastic toughening mechanism, thermophysical, and mechanical properties were systematically investigated. The (5RE 0.2 )TaO 4 ceramics have lower phonon thermal conductivity (1.2–2.6 W·m –1 ·K –1 ) in the entire temperature range than that of RETaO 4 and YSZ. (5RE 0.2 )TaO 4 has a higher fracture toughness and lower brittleness index than YSZ. The thermal expansion coefficients of (5RE 0.2 )TaO 4 are as high as 10.3 × 10 ‐6 K –1 at 1200°C and Young's modulus is 66–189 GPa, and thus, (5RE 0.2 )TaO 4 possesses great potential for application in thermal barrier coatings (TBCs).