Entropy‐Assisted Phase‐Ratio Engineering for Synergistic Thermo‐Mechanical Optimization of Dual‐Phase Niobate Ceramics

Single‐phase high‐entropy rare‐earth ceramics can effectively suppress phonon transport, yet their application in thermal barrier coatings (TBCs) is limited by the intrinsic trade‐off between thermal insulation and mechanical reliability. To overcome this limitation, an entropy‐assisted dual‐phase design strategy is proposed by coupling fluorite‐structured (Y 0.2 Sm 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 3 NbO 7 with monoclinic (Y 0.2 Sm 0.2 Dy 0.2 Er 0.2 Yb 0.2 )NbO 4 under identical high‐entropy compositions. The results reveal a clear phase‐function partitioning: the fluorite phase dominates phonon scattering and reduces thermal conductivity, whereas the monoclinic phase enhances thermal expansion adaptability and fracture tolerance. At an optimized phase ratio, the ceramic exhibits a low thermal conductivity of 1.37 W·m −1 ·K −1 , a high thermal expansion coefficient of 11.19 × 10 −6 K −1 at 1200°C, and an improved fracture toughness of 2.04 MPa·m 1/2 , demonstrating a favorable thermo‐mechanical synergy. This work highlights phase ratio as an effective design variable beyond single‐phase entropy optimization, offering a rational pathway for designing high‐performance TBC ceramics.