Synthesis, microstructure, and thermophysical properties of high-entropy rare earth cerium and zirconium cerates

Thermal barrier coatings improve the energy efficiency of industrial and aerospace gas turbines by increasing operating temperatures. In this study, two types of high-entropy thermal barrier coating materials were synthesized by solid-phase reactive sintering: (La 0.2 Nd 0.2 Gd 0.2 Yb 0.2 Y 0.2 ) 2 Ce 2 O 7 (5RC) and (La 0.2 Nd 0.2 Gd 0.2 Yb 0.2 Y 0.2 ) 2 CeZrO 7 (5RCZ). Both samples remain in a single-phase fluorite structure after annealing at 1400 °C for 100 h, showing excellent phase stability. Specifically, 5RC exhibits no chemical reaction with α-Al 2 O 3 following annealing at 1200 °C for 4 h and demonstrates outstanding chemical compatibility. The thermal expansion coefficients (TECs) for 5RC and 5RCZ are 11.5 × 10 −6  K −1 and 10.4 × 10 −6  K −1  at 1200 °C, respectively. Furthermore, the TEC of 5RCZ shows stable performance, demonstrating no significant fluctuations at lower temperatures. Due to the high entropy effect and lattice distortion, 5RC and 5RCZ exhibit excellent thermal insulating properties. At low-temperature range, 5RCZ has lower thermal conductivity than 5RC due to a more significant disorder in ion radius and atomic mass. At 1200 °C, the thermal conductivity of 5RCZ (1.406 W m −1  K −1 ) is greater than that of 5RC (1.263 W m −1  K −1 ), likely because of 5RC's higher infrared emissivity. In conclusion, the high-entropy rare earth ceramics 5RC and 5RCZ exhibit significant potential for use as thermal barrier coating materials.