High-entropy rare earth phosphates (REPO4, RE = Ho, Tm, Yb, Lu, Dy, Er and Y) with excellent comprehensive properties

High-entropy rare earth phosphates (HE REPO4, RE = Ho, Tm, Yb, Lu, Dy, Er and Y) with xenotime structure have been successfully synthesized and comprehensively characterized to evaluate their feasibility as thermal/environmental barrier coatings (T/EBCs) applied in SiCf/SiC ceramic matrix composites (SiC-CMCs). HE REPO4 show good chemical compatibility with SiO2 at 1400 °C and excellent high-temperature stability up to 1750 °C. The thermal expansion coefficient (TEC) of HE (6RE1/6)PO4 is 5.9 × 10−6/°C ranging from room temperature to 900 °C, which is close to that of SiC-CMCs. Compared with single-component REPO4, the thermal conductivity of HE (6RE1/6)PO4 (from 5.1 W·m−1·K−1 at 100 °C to 2.8 W·m−1·K−1 at 1300 °C) is significantly reduced benefiting from larger lattice distortion. These allow HE REPO4 to be a potential candidate as T/EBCs applied in SiC-CMCs.