Ten‐Cation High‐Entropy Rare‐earth Monosilicate: A Potential Thermal/Environmental Barrier Coating Material

High‐entropy rare‐earth monosilicates (HEREMSs) that exhibit both enhanced resistance to calcium‐magnesium‐aluminosilicate (CMAS) corrosion and optimized thermophysical properties are highly sought for next‐generation thermal/environmental barrier coatings (T/EBCs). Herein, we report the development of a novel 10‐cation HEREMS, i.e., (Lu 1/10 Yb 1/10 Tm 1/10 Er 1/10 Y 1/10 Ho 1/10 Dy 1/10 Tb 1/10 Gd 1/10 Eu 1/10 ) 2 SiO 5 (10‐cation HEREMS [10HEREMS]), with following comprehensive characteristics: (i) an ultralow thermal conductivity of 1.21 W·m −1 ·K −1 at room temperature, (ii) excellent thermal expansion compatibility with SiC f /SiC composites across 200−1500°C, and (iii) outstanding CMAS corrosion resistance (corrosion rate of 0.49 µm·h −1 ) up to 1600°C. These significant performance enhancements mainly result from intensified lattice distortion‐induced stress field fluctuations and phonon scattering to reduce thermal conductivity, strengthened multi‐cation lattice cohesion to decrease coefficients of thermal expansion, and suppressed dissolution kinetics of apatite in the CMAS melt to improve CMAS corrosion resistance. These remarkable multifunctional properties position 10HEREMS as a leading material for T/EBC applications.