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 ₂B ₂O 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) ₂O ₇, La ₂(ZnMgHfWMo) ₂O ₇ and La ₂(ZnMgSnWMo) ₂O 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) ₂O 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 ₂B ₂O 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.