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.

During flight, many silicates (sand, dust, debris, fly ash, etc.) are ingested by an engine. They melt at high operating temperatures on the surface of thermal barrier coatings (TBCs) to form calcium-magnesium-aluminum-silicate (CMAS) amorphous settling. CMAS corrodes TBCs and causes many problems, such as composition segregation, degradation, cracking, and disbanding. As a new generation of TBC candidate materials, rare-earth zirconates (such as Sm₂Zr₂O₇) have good CMAS resistance properties. The reaction products of Sm₂Zr₂O₇ and CMAS and their subsequent changes were studied by the reaction of Sm₂Zr₂O₇ and excess CMAS at 1350 ℃. After 1 h of reaction, Sm₂Zr₂O₇ powders were not completely corroded. The reaction products were Sm-apatite and c-ZrO₂ solid solution. After 4 h of reaction, all Sm₂Zr₂O₇ powders were completely corroded. After 24 h of reaction, Sm-apatite disappeared, and the c-ZrO₂ solid solution remained.

A series of Sm₂Zr₂O₇-SiC composites doped with different volume fraction and particle size of SiC were prepared by hot pressing at 1300 ℃. The phase of the composites prepared is P-Sm₂Zr₂O₇ and C-SiC, and no other diffraction peaks exist, which indicates that Sm₂Zr₂O₇ has great chemical compatibility with SiC. The thermal conductivity and phonon thermal conductivity of the Sm₂Zr₂O₇-SiC composites are measured by the laser pulse method. The photon thermal conductivity of the composites is obtained by subtracting the phonon thermal conductivity from the total thermal conductivity. The results show that the photon thermal conductivity of Sm₂Zr₂O₇-SiC composites is lower than that of pure Sm₂Zr₂O₇. The photon thermal conductivity of Sm₂Zr₂O₇-SiC composites decreases first and then increases with the increase of SiC particle size. Sm₂Zr₂O₇-(5 vol%, 10 μm)SiC composite has the lowest photon thermal conductivity.