Dual‐phase (Ho0.1Er0.1Yb0.4Lu0.4)₂SiO₅/Lu₂Si₂O₇ rare‐earth silicates with superior comprehensive properties

Exploiting high‐entropy rare‐earth monosilicates (HEREMs) with simultaneously improved corrosion resistance and thermophysical properties is vital for their use as next‐generation environmental barrier coating materials. Herein, a new dual‐phase strategy has been developed to regulate the comprehensive properties of HEREMs. Specifically, by adding 20% Lu 2 Si 2 O 7 (LuD) into (Ho 0.1 Er 0.1 Yb 0.4 Lu 0.4 ) 2 SiO 5 (HEREM‐0.1), novel (Ho 0.1 Er 0.1 Yb 0.4 Lu 0.4 ) 2 SiO 5 /Lu 2 Si 2 O 7 (HEREM‐0.1/LuD) dual‐phase rare‐earth silicates have been successfully fabricated to exhibit a synergistic enhancement in both thermophysical properties and calcium–magnesium–aluminosilicate (CMAS) corrosion resistance, including excellent high‐temperature stability without phase transformation up to 1973 K, well‐matched coefficients of thermal expansion (3.5–5.7 × 10 −6 K −1 ) with SiC f /SiC composites (4.0–5.5 × 10 −6 K −1 ) across 473–1573 K, extremely low thermal conductivity of 0.8–1.4 W m −1 K −1 from room temperature to 1273 K, and further enhanced CMAS corrosion resistance at 1673 K for 60 h (ultralow corrosion depth of 47 µm). Such superior properties can be attributed to the introduction of the dual‐phase structure and the enhanced stability of the formed apatite structure. Our work provides an alternative way to developing HEREMs with outstanding comprehensive properties.