Toward predictable phase structures in high-entropy oxides : A strategy for screening multicomponent compositions

The recent surge in interest in high-entropy oxides (HEOs) as a novel class of ceramic materials can be attributed to the remarkable performance enhancements caused by both the complexity of their chemical composition and the simplicity of their structure. The extensive range of components presents challenges to the implementation of HEOs, rendering it difficult to predict the phase structure prior to the final synthesis. Herein, semi-empirical methods based on various parameters, including ΔX, VEC, ΔS_mix, ΔH_mix and δ, were utilized to determine the phase stability of rock salt, spinel, perovskite and fluorite structures. The combination of δ with ΔX, VEC, ΔS_mix, and ΔH_mix, in graphical form, is an effective indicator for determining the phase stability of rock salt, perovskite and fluorite structures. The spinel structure is stabilized outside the range of the other three structures. The phase formation rules were further verified with two newly designed and prepared HEOs via X-ray diffraction and high-resolution transmission electron microscopy. The HEOs show potential for functional applications, e.g., methyl orange degradation.