Entropy-stabilized oxides

Abstract

Configurational disorder can be compositionally engineered into mixed oxide by populating a single sublattice with many distinct cations. The formulations promote novel and entropy-stabilized forms of crystalline matter where metal cations are incorporated in new ways. Here, through rigorous experiments, a simple thermodynamic model, and a five-component oxide formulation, we demonstrate beyond reasonable doubt that entropy predominates the thermodynamic landscape, and drives a reversible solid-state transformation between a multiphase and single-phase state. In the latter, cation distributions are proven to be random and homogeneous. The findings validate the hypothesis that deliberate configurational disorder provides an orthogonal strategy to imagine and discover new phases of crystalline matter and untapped opportunities for property engineering.

Charge compensation and electrostatic transferability in three entropy-stabilized oxides: Results from density functional theory calculations

“…Following up on the results of Rost et al, 15 Berardan et al reported that the single-phase, entropic rocksalt structure of J14 is maintained with the addition of Li and Li co-incorporated with Ga as substitutional (rather than interstitial) defects. 16,17 The former is commonly associated with a þ1 formal charge state, and so the authors suggest charge compensation involving oxidation of Co þ2 to Co þ3 and/or creation of O vacancies.…”

“…There are clearly tremendous possibilities for designing materials of this type with potentially interesting and unique properties and applications. [15][16][17] Zhang et al 3 demonstrated that the stability of nonoxide MHEAs can be reasonably predicted based on two empirical parameters that can be derived from the component elements, a measure of the differences in atomic radii and the mixing enthalpy for a solid solution. In addition, to enhance the free energy of the MHEAs the entropy of mixing should be maximized, which occurs for equi-molar concentrations.…”

“…In a recent set of experiments, Rost et al demonstrated a new class of material in which entropy drives the free energy landscape, an entropystabilized oxide (ESO). 15 The first system reported, which was termed the J14 composition, has a rocksalt structure with one of the face-centered cubic (fcc) sublattices containing oxygen anions, and the other sublattice containing randomly arranged Mg, Co, Ni, Cu, and Zn cations in equi-atomic proportions. In addition to being an oxide, this system is a unique combination of an ordered and a disordered sublattice together within a single high entropy phase.…”

High-Entropy Alloys: A Current Evaluation of Founding Ideas and Core Effects and Exploring “Nonlinear Alloys”

“…This result has been shown most directly in highentropy oxides. 38 This new perspective overturns many decades of neglect, where enthalpies have been the primary focus and the role of configurational entropy has never been systematically evaluated in phase selection. Establishing the role of configurational entropy as an adjustable parameter in phase engineering gives a more balanced, mature perspective that is a major success from the early HEA years.…”

Phase Evolution During Synthesis of Nanocrystalline Multicomponent (Co,Cu,Mg,Ni,Zn)O Metal Oxides with Varying ZnO Content

“…However, only doped, co-doped and binary ceramics have been extensively studied, while the area of equimolar, multicomponent ceramics has been a largely unexplored field until recently [1]- [3]. In this investigation, a multicomponent nanocrystalline ceramic oxide, (Co,Cu,Mg,Ni,Zn)O, was synthesised with the primary intention of studying the type and stability of the phases formed with systematically varying zinc oxide content.…”