Interfacial Stability between High-Entropy [sub.2]Zr[sub.2]O[sub.7] and Yttria-Stabilized Zirconia for Advanced Thermal Barrier Coating Applications

(La[sub.0.2]Yb[sub.0.2]Sm[sub.0.2]Eu[sub.0.2]Gd[sub.0.2])[sub.2]Zr[sub.2]O[sub.7] (HEZ) has shown considerable promise as a novel thermal barrier coating material for temperatures exceeding 1300 °C. This study systematically investigates the interfacial stability of (La[sub.0.2]Yb[sub.0.2]Sm[sub.0.2]Eu[sub.0.2]Gd[sub.0.2])[sub.2]Zr[sub.2]O[sub.7] with yttria-stabilized zirconia (YSZ), which is of paramount importance for its application in double-layer thermal barrier coatings. Our findings highlight that rare earth elements with a smaller radius diffuse more easily into the YSZ lattice, resulting in a broader diffusion zone. Simultaneously, the incorporation of rare earth elements into the YSZ lattice inhibits tetragonal-to-monoclinic phase transformation. Compared to La[sub.2]Zr[sub.2]O[sub.7]/YSZ, HEZ/YSZ demonstrates superior high-temperature stability, which could be attributed to the higher fracture toughness and lower thermal expansion coefficient of HEZ, the absence of t-m transformation and the formation of a continuous gradient diffusion layer that minimizes interface stress. This study offers a practical strategy for designing materials for durable double-layer thermal barrier coating systems.