High-Entropy Oxide Ceramics: Structure, Synthesis Methods, and Applications

Abstract

High-entropy materials represent a new class of multicomponent materials formed by mixing five or more elements. Owing to pronounced high-entropy effects, these materials exhibit unique physicochemical properties. In recent years, there has been a steady increase in interest in high-entropy materials, as evidenced by the growing number of scientific publications devoted to high-entropy alloys, ceramics, and oxides.

This review systematizes current knowledge on high-entropy oxide ceramics, presents data aimed at understanding the main types of crystal structures—rock salt, fluorite, perovskite, pyrochlore, spinel, and others—and discusses the principles of synthesis and application of high-entropy oxide ceramics. The role of high configurational entropy in stabilizing single-phase states, as well as the influence of chemical complexity on lattice distortion, diffusion processes, and the formation of the so-called “cocktail effect,” is demonstrated.

The paper outlines the main synthesis methods for high-entropy oxide ceramics, including solid-state, liquid-phase, and gas-phase techniques, and analyzes their effects on phase composition, microstructure, and material properties. The review covers recent studies on the mechanical, thermodynamic, catalytic, and electrochemical characteristics of high-entropy oxides (HEOs), as well as their applications in structural materials and coatings. Promising application areas of high-entropy oxide ceramics are discussed, including thermal barrier coatings, catalytic systems, electrical and ionic conductors, and materials designed for operation under extreme conditions.

The performed analysis reveals correlations between structure, synthesis methods, and properties of high-entropy oxides, providing a foundation for the development of new materials with tailored characteristics.