High-entropy (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 ceramic: A promising thermal barrier coating material

• (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 exhibits great high-temperature phase stability up to 1600 °C and excellent chemical compatibility with Al2O3 even at 1300 °C. ○ The grain growth rate of high entropy hafnate is more sluggish than that of Y2Hf2O7. ○ The thermal conductivity of (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 (0.73–0.93 W m −1 K −1 ) is much lower than those of components RE2Hf2O7 and many thermal barrier coating materials. ○ (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 can be as next generation thermal barrier coating material. Thermal barrier coating (TBC) materials perform an increasingly important role in the thermal or chemical protection of hot components in a gas turbine. In this study, a novel high entropy hafnate (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 was synthesized by solution combustion method and investigated as a potential TBC layer. The as-synthesized (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 possesses a pure single disordered fluorite phase with a highly homogeneous distribution of rare earth (RE) cations, exhibiting prominent phase stability and excellent chemical compatibility with Al 2 O 3 even at 1300 °C. Moreover, (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 demonstrates a more sluggish grain growth rate than Y 2 Hf 2 O 7 . The thermal conductivity of (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 (0.73-0.93 W m −1 K −1 ) is smaller than those of components RE 2 Hf 2 O 7 and many high entropy TBC materials. Beside, the calculated thermal expansion coefficient (TEC) of (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 (10.68 × 10 −6 /K, 1100 °C) is smaller than that of yttria-stabilized zirconia (YSZ). Based on the results of this work, (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 is suitable for the next generation TBC materials with outstanding properties.