Preparation, Microstructure, and Thermophysical Properties of a Novel (La, Nd, Tm, Yb, Lu)2Zr2O7 High-Entropy Ceramic for Thermal Barrier Coatings

Abstract

The concept of high entropy has brought new opportunities for designing and optimizing thermal barrier coating (TBC) materials for aircraft engines that meet higher thrust-to-weight ratios. Herein, two novel high-entropy rare-earth zirconates (HE-REZs) with the chemical formula of (La_0.2Nd_0.2Tm_0.2Yb_0.2Lu_0.2)₂Zr₂O₇ (La0.2) and (La_0.07Nd_0.07Tm_0.26Yb_0.3Lu_0.3)₂Zr₂O₇ (La0.07) are synthesized by solid-state reaction. Results show that the La0.2 sample is composed of defect fluorite and pyrochlore dual-phase structure and the La0.07 sample is single-phase defect fluorite structure. The average grain growth rates of La0.07 and La0.2 samples are much lower than that of La₂Zr₂O₇ (LZ) during annealing at 1300 °C for 100 and 200 h, which may be ascribed to the sluggish diffusion effect of high-entropy ceramics. Additionally, the thermal expansion coefficients of La0.07 and La0.2 at 1200 °C are 11.32 × 10⁻⁶ and 10.90 × 10⁻⁶ K⁻¹, respectively. The thermal conductivity of La0.07 sample is 1.41 W m⁻¹ K⁻¹ at 1000 °C, which is 28% lower than that of LZ (1.97 W m⁻¹ K⁻¹), while that of La0.2 sample is 2.27 W m⁻¹ K⁻¹. This work provides a new insight into developing novel single-phase and dual-phase HE-REZ ceramics with higher thermophysical properties, which would be significant in material development for TBCs.