Structure and properties of RE₂HE₂O₇ thermal barrier ceramics designed with high-entropy at different sites

Yttria-stabilised zirconia is used as a thermal barrier coating material and is widely applied in the thermal protection field. However, its tendency to undergo phase transformation at high temperatures poses a significant challenge to the durability of these coatings. An alternative material with superior high-temperature phase stability and a high coefficient of thermal expansion is thus desirable. Rare earth zirconate, such as Gadolinium zirconate (Gd₂Zr₂O₇), has emerged as a promising candidate due to its inherent properties. High-entropy ceramics have attracted much attention due to their excellent properties. Leveraging the design principles of high-entropy systems, the structural configuration of Gd₂Zr₂O₇ has been optimised to enhance its properties. In this work, A-, B- and AB-sites of Gd₂Zr₂O₇ were designed by regulating the configurational entropy. Based on this strategy, seven types of high-entropy powders and ceramic blocks were prepared successfully. The structure and thermal properties of the as-prepared samples were investigated. The results indicate that the configurational entropy within the system and the size disorder parameter are pivotal in determining the thermal stability and thermal conductivity of the as-prepared high-entropy ceramic materials. Notably, the dual-phase high-entropy Gd₂(Ce_0.2Zr_0.2Hf_0.2Sn_0.2Ti_0.2)₂O₇ ceramic exhibits good thermal stability. The large size and mass difference between the elements results in a reduced mean free path of phonons, thereby reducing the thermal conductivity significantly. The Gd₂(Ce_0.2Zr_0.2Hf_0.2Sn_0.2Ti_0.2)₂O₇ ceramic demonstrates thermal conductivity that is substantially lower than that of Gd₂Zr₂O₇ and other high-entropy ceramics, which is as low as 0.927–0.850 W m⁻¹ K⁻¹ at 200–800°C. These results indicate that the high-entropy Gd₂(Ce_0.2Zr_0.2Hf_0.2Sn_0.2Ti_0.2)₂O₇ is an outstanding candidate for application in thermal barrier technology and related fields.