High-entropy (La_0.2Nd_0.2Sm_0.2Eu_0.2Gd_0.2)₂Ce₂O₇: A potential thermal barrier material with improved thermo-physical properties

High-entropy oxides (HEOs) are widely researched as potential materials for thermal barrier coatings (TBCs). However, the relatively low thermal expansion coefficient (TEC) of those materials severely restricts their practical application. In order to improve the poor thermal expansion property and further reduce the thermal conductivity, high-entropy (La_0.2Nd_0.2Sm_0.2Eu_0.2Gd_0.2)₂Ce₂O₇ is designed and synthesized in this work. The as-prepared multicomponent material is formed in a simple disordered fluorite structure due to the high-entropy stabilization effect. Notably, it exhibits a much higher TEC of approximately 12.0 × 10^-6 K^-1 compared with those of other high-entropy oxides reported in the field of TBCs. Besides, it presents prominent thermal insulation behavior with a low intrinsic thermal conductivity of 0.92 W·m^-1·K^-1 at 1400 ℃, which can be explained by the existence of high concentration oxygen vacancies and highly disordered arrangement of multicomponent cations in the unique high-entropy configuration. Through high-temperature in-situ X-ray diffraction (XRD) measurement, this material shows excellent phase stability up to 1400 ℃. Benefiting from the solid solution strengthening effect, it shows a higher hardness of 8.72 GPa than the corresponding single component compounds. The superior thermo-physical performance above enables (La_0.2Nd_0.2Sm_0.2Eu_0.2Gd_0.2)₂Ce₂O₇ a promising TBC material.