Tailoring thermal and mechanical properties of rare earth niobates by coupling entropy and composite engineering

Abstract

In this paper, a series of high-entropy rare earth niobates, including fluorite RE3NbO7 (HE317), monoclinic RENbO4 (HE114) and RENbO4/RE3NbO7 composite (HE-composite), are prepared via solid state reaction, following by a study about their thermal and mechanical properties. The high-entropy rare earth niobates exhibit excellent phase stability after thermally exposed to 1300 °C for 100 h, indicating entropy can stabilized high-entropy rare earth niobates. Compared with the single element rare earth niobates, high-entropy rare earth niobates have higher fracture toughness and hardness. The high-entropy RENbO4/RE3NbO7 composite has the best mechanical properties, with a fracture toughness of 2.71 ± 0.17 MPa·m1/2 and hardness of 9.46 ± 0.24 GPa, respectively. The high-entropy niobates exhibit high coefficients of thermal expansion which is close to 7 wt% Y2O3 stabilized ZrO2. It is also proved that the configurational entropy has little effect on the critical temperature from monoclinic to tetragonal phase transition. The thermal conductivity of HE-composite is lower than HE114, indicating the combination of HE114 and H317 is a more efficient strategy to decrease the thermal conductivity of HE114 than entropy engineering.