Reduced high-temperature thermal conductivity of high-entropy rare-earth zirconate via suppressing infrared thermal radiation

High-entropy rare-earth zirconates have attracted much attention as potential thermal barrier coating materials due to their low thermal conductivity and high-temperature phase stability. However, the thermal conductivity of rare-earth zirconates as infrared semitransparent materials increases due to thermal radiation at high temperatures. To address this issue, a series of high-entropy rare-earth zirconate composite ceramics with varying lanthanum phosphate contents [(La_0.25Eu_0.25Gd_0.25Yb_0.25)₂(Zr_0.75Ce_0.25)₂O₇/LaPO₄] were prepared in this paper and their high-temperature thermal properties were analyzed. The results indicate that lanthanum phosphate in dual-phase ceramics effectively reduces infrared transmittance of materials, thereby decreasing high-temperature thermal conductivity. Compared to high-entropy rare-earth zirconate, the temperature at which the dual-phase ceramics exhibits the lowest thermal conductivity shifted from 673 K to 973 K, with no significant increase in high-temperature thermal conductivity. The infrared transmittance of composite ceramics is significantly reduced due to the strong scattering effect induced by the birefringence property of lanthanum phosphate and the refractive index difference between the two phases, thus markedly enhancing the high-temperature thermal insulation performance of the material. Moreover, the composite retains excellent Young's modulus and hardness with minor lanthanum phosphate. Consequently, the novel dual-phase ceramics hold potential as next-generation thermal barrier coating materials.