A Promising High-Entropy Thermal Barrier Material with the Formula (Y 0.2 Dy 0.2 Ho 0.2 Er 0.2 Yb 0.2 ) 3 Al 5 O 12 .

YSZ has been widely used as a TBC material, but its phase change at high temperatures limits its development, thus the need for developing new thermal barrier materials resistant to high temperatures. Rare-earth aluminate ceramics with a garnet structure (Yb 3 Al 5 O 12 ) have been considered as a potential thermal barrier material. The melting point of Yb 3 Al 5 O 12 is 2000 °C, which has a potential high temperature application prospect. However, Yb 3 Al 5 O 12 has lower thermal expansion and higher thermal conductivity than YSZ, which is a widely employed thermal barrier coating (TBC) material. To overcome these obstacles, (Y 0.2 Dy 0.2 Ho 0.2 Er 0.2 Yb 0.2 ) 3 Al 5 O 12 , a high-entropy ceramic, was prepared by a solid-state reaction and pressureless sintering. The thermal conductivity of the (Y 0.2 Dy 0.2 Ho 0.2 Er 0.2 Yb 0.2 ) 3 Al 5 O 12 was 3.48 W/(m·K) at 300 K, approximately 25.48% lower than that of the Yb3Al5O12 (4.67 W/(m·K)). The thermal expansion coefficient of the (Y 0.2 Dy 0.2 Ho 0.2 Er 0.2 Yb 0.2 ) 3 Al 5 O 12 was 9.28 × 10 -6 K -1 at 673-1273 K, approximately 18.52% higher than that of the Yb 3 Al 5 O 12 (7.83 × 10 -6 K -1 , 673-1273 K). When the (Y 0.2 Dy 0.2 Ho 0.2 Er 0.2 Yb 0.2 ) 3 Al 5 O 12 was annealed at 1550 °C for 7 days, its average grain size only increased from 0.7 μm to 1.3 μm. Moreover, the (Y 0.2 Dy 0.2 Ho 0.2 Er 0.2 Yb 0.2 ) 3 Al 5 O 12 exhibited better chemical stability and a lower grain growth rate than the Yb 3 Al 5 O 12 . This study reveals that (Y 0.2 Dy 0.2 Ho 0.2 Er 0.2 Yb 0.2 ) 3 Al 5 O 12 is a promising candidate for the future generation of thermal barrier materials.