Phase Separation in Metal Oxides

A fascinating phenomenon, recently found to occur in certain transition‐metal oxides, is phase separation wherein pure, nominally monophasic oxides of transition metals with well‐defined compositions separate into two or more phases over a specific temperature range. Such phase separation is entirely reversible, and is generally the result of a competition between charge‐localization and ‐delocalization, the two situations being associated with contrasting electronic and magnetic properties. Coexistence of more than one phase, therefore, gives rise to electronic inhomogeneity and a diverse variety of magnetic, transport, and other properties, not normally expected of the nominal monophasic composition. An interesting feature of phase separation is that it covers a wide range of length scales anywhere between 1–200 nm. While cuprates and manganates, especially the latter, provide excellent examples of phase separation, it is possible that many other transition‐metal compounds with extended structures will be found to exhibit phase separation.