Thermophysical and mechanical modulation of RE3NbO7 ceramics via compositional entropy design

High-entropy ceramics, renowned for their exceptional thermal insulation and stability, hold significant potential for thermal barrier coating applications in extreme environments. In this study, two rare-earth niobate ceramics—(Sc 1/4 Ho 1/4 Er 1/4 Yb 1/4 ) 3 NbO 7 (SHEY) and (Sc 1/5 Gd 1/5 Ho 1/5 Er 1/5 Yb 1/5 ) 3 NbO 7 (SGHEY)—were synthesized via solid-state reaction. The influence of rare-earth element composition on the thermal and mechanical properties was systematically investigated. SHEY and SGHEY exhibit nearly identical thermal expansion coefficients (TEC), with TECs at 1200 °C of 10.57 × 10 -6 K -1 and 10.52 × 10 -6 K -1 , respectively, indicating good thermal expansion matching with typical substrate and bond-coat materials in thermal barrier coating systems. Compared with SHEY, SGHEY possesses a finer grain size (3.17 μm vs. 4.70 μm), lower thermal conductivity at 1200 °C (1.38 vs. 1.76 W·m -1 ·K -1 ), and slightly higher fracture toughness (1.34 vs. 1.31 MPa·m 1/2 ), suggesting that incorporating Sc and Gd improves the balance between thermal insulation and mechanical robustness in the high-entropy niobate system.