A review about w{\"u}stite Fe 1-z O, pseudo-phases and defect clustering

TL;DR

This review comprehensively discusses the thermodynamic properties, phase diagram complexity, defect structures, and pseudo-phase transformations of non-stoichiometric wüstite Fe₁₋zO, highlighting recent advances since 1960.

Contribution

It synthesizes experimental and theoretical insights into defect clustering, pseudo-phase stability, and phase transitions in wüstite, clarifying the nature of its complex equilibrium behavior.

Findings

Identification of the W to W' phase transition near 1185 K

Reexamination of defect cluster transformations and their role in pseudo-phase stability

Development of equilibria models explaining defect and electronic charge carrier changes

Abstract

Thermodynamic properties and structural aspects of the non-stoichiometric w\"ustite Fe 1-z O, and its modifications-the so-called pseudo-phases-as functions of composition z and equilibrium temperature are reviewed from 1960 to present (159 references). The focus is first put on the complexity of the equilibrium phase diagram. The first order transition W $\rightleftharpoons$ W' is specified on the boundary iron/ w\"ustite close to 1185 K. Transitions correlated to the modifications Wi at T(W) > 1185 K and W'j at 1185K < T(W') < T(W) (i and j =1,2,3) are reexamined. Structural determinations based on point defects and their clustering are recalled. A series of equilibria are developed, trying to justify the stabilization of the pseudo-phases, which can be interpreted in terms of transformation of defect clusters, or their mode of distribution (percolation, superstructure) including changes in electronic charge carriers.