Calcium-magnesium-alumina-silicate (CMAS) resistant high entropy ceramic (Y0.2Gd0.2Er0.2Yb0.2Lu0.2)2Zr2O7 for thermal barrier coatings

A novel high-entropy material, (Y0.2Gd0.2Er0.2Yb0.2Lu0.2)2Zr2O7 was successfully synthesized by the solid state reaction method and spark plasma sintering, and investigated as a promising thermal barrier coating material. Rare-earth elements were distributed homogeneously in the pyrochlore structure. It was found that the prepared high-entropy ceramic maintains pyrochlore structure at the temperature up to 1600 °C, and it possesses a similar thermal expansion coefficient (10.2 × 10−6 K−1 at 25–900 °C) to that of YSZ, low thermal conductivity (< 0.9 W m−1 K−1 at 100–1000 °C) and good CMAS resistance (infiltration depth is 22 μm after annealed at 1300 °C for 24 h). The corrosion process was investigated, and RE elements distributing homogeneously in (Y0.2Gd0.2Er0.2Yb0.2Lu0.2)2Zr2O7 show different diffusion rates in CMAS. RE3+ with a larger radius (closer to Ca2+) is easier to react with CMAS to form an apatite phase.