Extreme-mixing-boosted CMAS corrosion resistance and thermophysical properties in high-entropy rare-earth disilicates

Superior calcium-magnesium-alumino-silicate (CMAS) corrosion resistance, along with favorable thermophysical properties, is crucial for high-entropy rare-earth disilicates (HEREDSs) to be used as environmental barrier coatings. To achieve this goal, we expand the composition space of HEREDSs and develop 9- to 16-cation HEREDSs using a laser-driven synthesis technique. Specifically, the intensified sluggish diffusion effect induced by extreme elemental mixing and the superior stability of the F-type phase in HEREDSs is beneficial for reducing the dissolution rate of the formed multicomponent apatite in the CMAS melt, while the inclusion of more elements with great atomic weight differences can induce phase separation, leading to deteriorated corrosion behavior. As a result, the synthesized (Lu, Yb, Tm, Er, Ho, Dy, Gd, Sm, Nd, Pr, Ce, La, Eu, Tb)₂Si₂O₇ (14HEREDS) is found to demonstrate superior CMAS corrosion resistance with a low corrosion rate of 6.7 μm h^-1 at 1400 °C for 48 h. Moreover, remarkable thermophysical properties, including superior phase stability over 1600 °C, extremely low room temperature thermal conductivity (1.05 W m^-1 K^-1), and excellent match of coefficient of thermal expansion (5.4 × 10^-6 K^-1) with SiC_f/SiC composites (4.5-5.5 × 10^-6 K^-1), are observed in the synthesized 14HEREDS. Our work develops a novel material with remarkable CMAS corrosion resistance and thermophysical properties, showing great promise for environmental barrier coating applications.