High-entropy(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))2Hf_(2)O_(7) ceramic: A promising 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 yttriastabilized 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.

Thermophysical properties of a novel high entropy hafnate ceramic

High-entropy oxides(HEOs)are considered promising thermal barrier coating(TBC)materials due to their unique thermophysical performances induced by the entropy effects.In this work,(La_(0.2)Ce_(0.2)Pr_(0.2)Sm_(0.2)Eu_(0.2))_(2)Hf_(2)O_(7)high entropy hafnate,as a thermal barrier coating(TBC)material,was successfully synthesized by solution combustion method for the first time.From the X-ray diffraction,scanning electron microscopy,and transmission electron microscopy results,it is confirmed that(La_(0.2)Ce_(0.2)Pr_(0.2)Sm_(0.2)Eu_(0.2))_(2)Hf_(2)O_(7)has pure single-phase ordered pyrochlore structure with highly homogeneous composition at both micrometer and nanometer scales.The synthesized(La_(0.2)Ce_(0.2)Pr_(0.2)Sm_(0.2)Eu_(0.2))2 Hf2O7 possesses excellent phase stability at 1600℃and demonstrates a low thermal conductivity(1.0-1.24 W·m^(-1)·K^(-1))which is lower than those of rare earth hafnates(RE2Hf2O7,RE=La,Ce,Pr,Sm,Eu).Therefore,it provides a new perspective and potential to prompt the next generation TBC materials with better performance.