Tailoring thermal and mechanical properties of non‐equimolar high‐entropy rare‐earth zirconates

ABSTRACT This study investigated non‐equimolar high‐entropy rare‐earth zirconate ceramics as candidates for next‐generation thermal barrier coatings (TBCs). Three compositions—(La 0.05 Eu 0.2 Ho 0.2 Y 0.2 Yb 0.35 ) 2 Zr 2 O 7 (La 0.05 ), (La 0.2 Eu 0.2 Ho 0.2 Y 0.2 Yb 0.2 ) 2 Zr 2 O 7 (La 0.20 ), and (La 0.35 Eu 0.2 Ho 0.2 Y 0.2 Yb 0.05 ) 2 Zr 2 O 7 (La 0.35 )—were synthesized to investigate the effects of non‐equimolar composition on structure and properties. X‐ray diffraction and scanning electron microscopy analyses reveal that non‐equimolar design induces phase evolution, grain refinement, and elemental segregation. La 0.05 exhibits the lowest thermal conductivity (1.19 W·m −1 ·K −1 at 800°C), attributed to enhanced phonon scattering, oxygen vacancy defects, and Yb 3+ ‐induced rattling effects. In contrast, La 0.35 shows the highest thermal expansion coefficient (11.44 × 10 −6 K −1 at 1200°C), hardness (13.07 ± 0.06 GPa), and fracture toughness (1.93 ± 0.05 MPa·m 1/2 ), benefiting from lattice distortion and dual‐phase interface toughening. These results demonstrate that non‐equimolar design enables coordinated tuning of entropy, structure, and microstructure, providing a practical strategy for optimizing TBC performance.