Physicochemical Properties of High‐Entropy Oxides

Abstract

The development of industry has triggered an increasingly severe demand for new functional materials. In recent years, researches on high‐entropy oxides (HEOs) are more comprehensive and in‐depth, and their fascinating properties are gradually known to the public. The unique elemental synergistic effect and lattice distortion endow the high‐entropy family with various untapped potential, and wide application fields and outstanding performance of HEOs make them candidates for future materials. In this review, the concept, structure, and synthesis of HEOs are firstly highlighted. Secondly, a variety of excellent properties and applications in the fields of mechanics, electrics, thermotics, optics and magnetics are summarized. This work provides a comprehensive overview about HEOs, facilitating the development of modern functionalities of the high‐entropy family.

Understanding the lithiation mechanism of Li2O-doped spinel high-entropy oxides as anode materials for Li-ion batteries

“…9–11 Thus, HEOs can be defined as single-phase oxide solid solutions consisting of five or more different cations occupying the same Wyckoff position in the crystal with similar molar proportions to obtain a high S config for the system. 8,12,13 The high S config endows HEOs with excellent physicochemical properties, such as the most typical entropy-induced phase stabilization effect, a sluggish diffusion effect, a lattice distortion effect, and a “cocktail” effect. 14–17 These unique properties mean HEOs exhibit great research value in the fields of energy storage, catalysts, and magnetic materials.…”

“…as active species can provide cycling capacity, while using non-active species such as Mg and Al as buffer materials can stabilize the lattice structure, suppress volume expansion, and ensure good cycling stability. 13,26 The performance of an HEO is closely related to the metal cations; therefore, by adjusting the types of cations, it is possible to regulate the crystal structure and properties of the HEO anode, providing a modular approach for the design and performance regulation of anode materials in the field of LIBs. 16,18,25…”

Spin-Cluster Glassy and Long-Range Ordered Magnetic States in Honeycomb-Layered Compositionally Complex Oxides Na3–xLixT2SbO6 (T = Cu1/3Ni1/3Co1/3)

“…A rapidly growing class of high-entropy oxides (HEOs) attracts much attention because many of them display interesting and useful properties (catalytic, dielectric, optical, magnetic, and electrode behavior, ionic conductivity, low thermal conductivity, etc.) that usually cannot be predicted based on the properties of corresponding constituents. − HEOs are often considered as entropy-stabilized oxides (ESOs), but actually, these two classes overlap only partially . The seminal work by Rost et al introduced rock salt-type Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 O that is both HEO and ESO because individual CuO and ZnO do not belong to the rock salt type.…”

“…Therefore, their five- or six-component solid solutions will be HEO but not ESO. It is now commonly adopted that HEOs are solid solutions combining on a single site at least four or five , different cations in (approximately) equal fractions, irrespective of the entropy stabilization.…”

“…From the cited recent reviews, − it is evident that magnetic studies of HEOs are now concentrated on a rather short list of structure types: those of spinel, perovskite, and rock salt, with rare or solitary works on magnetoplumbite-, bixbyite-, and pyrochlore-type phases. We only can add three reports on magnetism in high-entropy REBa 2 Cu 3 O 7– y , and wolframite- and Zn 2 Mo 3 O 8 -type materials …”