Exploring The Landscape of High Entropy Oxides

High entropy, multi-component metal alloys (HEA), have superior mechanical properties and high radiation tolerances; which are, in part, driven by configurational entropy. Recently, an oxide analogue comprised of MgO, CoO, NiO, CuO and ZnO was synthesized; exhibiting a truly entropy-stabilized, reversible phase transition from a multiphase material to a single rock salt-ordered phase above 850-900°C. This entropy-driven stabilization may engender many unique properties, such as high melting temperatures, radiation resistance and other anomalous responses. Here, we discuss a design strategy for the prediction of synthesizable disordered oxides. Our effort employs first principles studies of 2-component oxides to develop design rules based on the relationship between pairwise enthalpies of formation, ΔH, and configurational entropy of the disordered material. A similar chemical identity-to-ΔH map was previously explored using the class of high entropy alloys, where the stability of multicomponent metal alloys was correlated to the enthalpy of mixing of binary and ternary compounds. Combining these pairwise formation enthalpies with Monte Carlo simulations we are able to explore the temperature dependent phase transitions within these materials. We further extend this concept to exploring the role of temperature and oxygen partial pressure thus allowing for the synthesis of metastable phases such as the recently synthesize Fe-based high entropy oxides. This work presents a roadmap for the discovery of a host of new entropy stabilized materials.<br/><br/>This work was supported by the U.S. D.O.E., Office of Science, BES, MSED (first principles calculations) and the LDRD Program of ORNL (simulations), managed by UT-Battelle, LLC, for the U. S. DOE using resources at NERSC and OLCF.