Synthesis of high-entropy La2B2O7 ceramics with non-equivalent principal elements in B-sites and their CMAS resistance performance

A new method is proposed to predict the formation of high-entropy single-phase oxide with a pyrochlore structure synthesis from non-equivalent principal elements. Based on this concepte, the La 2 B 2 O 7 (B = Zn 2+ , Mg 2+ /Ni 2+ , Ce 4+ /Zr 4+ /Hf 4+ /Sn 4+ /Ti 4+ , W 6+ , Mo 6+ ) were designed, in which high-entropy La 2 (ZnMgZrWMo) 2 O 7 , La 2 (ZnMgHfWMo) 2 O 7 and La 2 (ZnMgSnWMo) 2 O 7 pyrochlore ceramics were successfully prepared by solid-phase sintering. The microstructure of the entropy-stabilized phase was demonstrated using X-ray diffraction and elemental mapping, and the thermal properties including the thermal expansion coefficient and thermal conductivity were analyzed. The results show that La 2 (ZnMgZrWMo) 2 O 7 has a higher thermal expansion coefficient (13.9 × 10 –6 K –1 ) and lower thermal conductivity (0.8 W/m·K) than its corresponding single-components compound. In addition, La 2 B 2 O 7 (B = Zn 2+ , Mg 2+ , Zr 4+ /Hf 4+ /Sn 4+ , W 6+ , Mo 6+ ) pyrochlore high-entropy ceramics exhibit good calcium – magnesium – aluminosilicate (CMAS) resistance, the apatite protective layer generated after the reaction of La with CMAS effectively prevents further corrosion. This study suggests a novel method for predicting the formation of high-entropy single-phase oxides of pyrochlore structures and provides a new design concept for anti-CMAS corrosion materials.