Colossal dielectric constant in high entropy oxides

TL;DR

This paper demonstrates that high entropy oxides can exhibit colossal dielectric constants, expanding their potential for use as large-k dielectric materials through aliovalent substitution and charge compensation mechanisms.

Contribution

It introduces the possibility of aliovalent substitution in high entropy oxides, significantly broadening their compositional and functional diversity.

Findings

High entropy oxides can have colossal dielectric constants.

Aliovalent substitution is feasible with charge compensation.

Potential for new large-k dielectric materials is demonstrated.

Abstract

Entropic contributions to the stability of solids are very well understood and the mixing entropy has been used for forming various solids, for instance such as inverse spinels. A particular development was related to high entropy alloys in which the configurational disorder is responsible for forming simple solid solutions and which are thoroughly studied for various applications especially due to their mechanical properties but also electrical properties, hydrogen storage, magnetic properties. Many unexplored compositions and properties still remain for this class of materials due to their large phase space. In a recent report it has been shown that the configurational disorder can be used for stabilizing simple solid solutions of oxides, which should normally not form solid solutions, these new materials were called "entropy-stabilized oxides". In this pioneering report, it was shown that mixing five equimolar binary oxides yielded, after heating at high temperature and quenching, an unexpected rock salt structure compound with statistical distribution of the cations in a face centered cubic lattice. Following this seminal study, we show here that these high entropy oxides (named HEOx hereafter) can be substituted by aliovalent elements with a charge compensation mechanism. This possibility largely increases the potential development of new materials by widening their (already complex) phase space. As a first example, we report here that at least one HEOx composition exhibits colossal dielectric constants, which could make it very promising for applications as large-k dielectric materials.