(Lu_1/7Yb_1/7Sc_1/7Er_1/7Y_1/7Ho_1/7Dy_1/7)₂Si₂O₇ high entropy rare-earth disilicate with low thermal conductivity and excellent resistance to CMAS corrosion

Low thermal conductivity, compatible thermal expansion coefficient, and good calcium–magnesium–aluminosilicate (CMAS) corrosion resistance are critical requirements for environmental barrier coatings used on silicon-based ceramics. RE₂Si₂O₇ (RE = rare earth) has been widely recognized as one of the most promising candidates for environmental barrier coatings due to its good water vapor corrosion resistance. However, the relatively high thermal conductivity and poor resistance to CMAS corrosion have limited its practical application. Inspired by the high entropy effect, in this work, a novel rare earth disilicate (Lu_1/7Yb_1/7Sc_1/7Er_1/7Y_1/7Ho_1/7Dy_1/7)₂Si₂O₇ ((7RE_1/7)₂Si₂O₇) has been designed and synthesized by a solid reaction process. (7RE_1/7)₂Si₂O₇ showed a low thermal conductivity of 1.81 W·m⁻¹·K⁻¹ at 1273 K. Furthermore, the thermal expansion coefficient of (7RE_1/7)₂Si₂O₇ (4.07×10⁻⁶ ℃⁻¹ from room temperature (RT) to 1400 ℃) is close to that of the SiC-based ceramic matrix composites (SiC-CMCs) ((4.5–5.5)×10⁻⁶ ℃⁻¹). Additionally, (7RE_1/7)₂Si₂O₇ exhibited excellent resistance to CMAS corrosion. When exposed to CMAS at 1300 ℃ for 48 h, the reaction layer thickness was 22 μm. The improved performance of (7RE_1/7)₂Si₂O₇ highlights its potential as a promising candidate for thermal/environmental barrier coatings.