Metal to insulator transitions in 3d-band correlated oxides containing Fe composition

The metal to insulator transitions (MIT) as achieved in 3d-band correlated transitional metal oxides triggers abrupt variations in the electrical, optical and/or magnetic properties, beyond conventional semiconductors. Among such material families, the ion (Fe: 3d⁶4s²) containing oxides are interesting owing to their widely tunable MIT properties associated with various valance states of Fe, while their potential electronic applications are also promising noticing the large abundance of Fe on earth. Representative MIT properties triggered by critical temperature (T_MIT) were reported for ReFe₂O₄ (Fe^2.5+), ReBaFe₂O₅ (Fe^2.5+), Fe₃O₄ (Fe^2.67+), Re_1/3Sr_2/3FeO₃ (Fe^3.67+), ReCu₃Fe₄O₁₂ (Fe^3.75+) and Ca_1-xSr_xFeO₃ (Fe⁴⁺). It is also interesting to note the common feature in MITs of these Fe containing oxides that are usually accompanied by the charge ordering transitions or disproportionation associated with the valance states of Fe. Herein, we review the material family of the Fe-containing MIT oxides, their MIT functionalities and the respective mechanisms. From the perspective of potential correlated electronic applications, the tunability in the critical temperatures associated with MIT (T_MIT) and its resultant resistive change are summarized for the Fe-containing oxides and further compared to other materials exhibiting the MIT functionality. In particular, we highlight the abrupt MIT and wide tunability in T_MIT for the Fe-containing quadruple perovskites, such as ReCu₃Fe₄O₁₂, while their more effective material synthesis is yet required to be further explored to cater for potential applications.