Spark plasma sintering of (5RE.2)Ta3O9 high-entropy ceramics and their thermal properties

Six rare-earth tantalate high-entropy ceramics of (5RE .2 )Ta 3 O 9 (RE represents any five elements selected from La, Ce, Nd, Sm, Eu, Gd) were designed and prepared by spark plasma sintering process at 1400°C in this study. The (5RE .2 )Ta 3 O 9 ceramics only consist of a single-phase solid solution with perovskite structure. Their relative densities are all above 90%, and the average grain size is in the range of 1.47–2.92 μm. The thermal conductivity of (5RE .2 )Ta 3 O 9 ceramics is in 2.24–1.90 W m −1 K −1 (25°C–500°C), which is much lower than that of yttria-stabilized zirconia. In six samples, (La .2 Nd .2 Sm .2 Gd .2 Eu .2 )Ta 3 O 9 possesses a thermal conductivity of 1.90 W m −1 K −1 , a thermal expansion coefficient of 3.47 × 10 −6 K −1 (500°C), a Vickers hardness of about 7.33 GPa, and a fracture toughness of about 5.20 MPa m 1/2 , which are suitable for its application as thermal barrier coatings.