Composition design, thermodynamic calculation and synthesis of rocksalt structure Mg–Co–Ni–Cu–Zn–O HEOs based on cluster-plus-glue-atom model

Multi-component high entropy oxides (HEOs) have attracted enormous attention due to their unique structures and potential applications. The conventional selection strategy to obtain HEOs is to search for equimolar cationic systems to maximize configurational entropy and avoid phase separation. We previously explored non-equimolar cationic rocksalt structure Mg–Co–Ni–Cu–Zn–O HEOs using cluster-plus-glue-atom model. In this paper, the mixing entropy, enthalpy and Gibbs free energy of constructed superclusters were numerically calculated and compared with the correlated crystal structure based on recent studies. It indicated the Gibbs free energy rather than mixing entropy agrees well with the phase stability of HEOs. Mg28Co17Ni19Cu16Zn16O96 shows the optimal phase stability which is related to the lowest Gibbs free energy, reflecting a regular octahedral environment preferred by the cation composition in the system. Enthalpy and entropy are among important design criteria in determining the phase stability of HEOs but the function of enthalpy is obviously higher than that of entropy. This study provides a comprehensive way to access HEOs which is undoubtedly very important for the development of other non-equimolar cationic high entropy materials such as carbides, silicides, borides or nitrides.