Composition Optimization of Yb-Doped GdPO4 for Thermal/Environmental Barrier Coating Applications

Thermal/environmental barrier coating (T/EBC) protects ceramic matrix composites (CMC) from environmental corrosion and provides thermal insulation simultaneously. As a newly developed TBC material, GdPO4 has attracted much attention due to its low thermal conductivity, but its relatively high thermal expansion coefficient (TEC) limits the application in the T/EBC system. In this study, Yb-doped GdPO4 with properties desirable for the T/EBC system is proposed. The high-temperature stability and mechanical and thermophysical properties of Gd1−xYbxPO4 (x = 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875 and 1) were studied, and the mechanism for doping modification was fully explained. Gd0.75Yb0.25PO4 with Young’s modulus of 82 GPa and thermal conductivity of 1.01 W·m−1·K−1 is considered to have the most desirable properties. Compared with GdPO4, the TEC of Gd0.75Yb0.25PO4 (6.3 × 10−6 K−1) is reduced by ~39%, and the fracture toughness is improved by ~30%. Therefore, Gd0.75Yb0.25PO4 is considered to be suitable for usage as a T/EBC material.