Entropy stabilized multicomponent oxides with diverse functionality – a review

Over the last few years, high-entropy oxides (HEOs) are subjected to considerable scientific scrutiny due to their exceptional characteristics, tunable properties displaying remarkable performance including colossal dielectric constant, low electrical and thermal conductivity, high-temperature phase stability, excellent magnetic, structural optical properties and extraordinary catalytic behavior. The single-phase crystal structure of multicomponent oxides is stabilized via configurational entropy (Sconfig). An incrementation in the number of elements magnifies Sconfig which dominates the free energy landscape, overcomes enthalpy in Gibb’s free energy, and reaches a maximum magnitude while entire elements are in equiatomic fractions. Therefore, accurate control of configurational entropy is the main motive force used to achieve phase pure HEOs by the incorporation of more than four cations in the system in equiatomic proportions with random distributions. HEOs are becoming hotcakes in the field of research as it emphasizes on compositions proximally near the centers of the multicomponent phase diagram, where unexpected behaviors can be anticipated. Thus, presenting a crucial research frontier for the material scientists to explore. As the novel design approach of entropy stabilization is still immature, these new oxide candidates can be engineered for practical applications in batteries, capacitors, nuclear reactors, and thermal barrier coatings. This review addresses the properties like electrochemical, electrical, magnetic, mechanical, catalytic, thermal, etc., of HEOs to date, with additionally focusing on their classification, theoretical predictions, and fundamental understanding of entropy engineering including entropy dominated phase stabilization effect.