Variation in electrical conductivity of A2Fe2O5 (A = Sr, Ba): the role of structural order

The significant impact of structural order on electrical properties of oxygen-deficient perovskites has been demonstrated through investigation of Sr2Fe2O5 and Ba2Fe2O5. The vacant sites created due to oxygen-deficiency are known to order differently in these two materials, leading to different structures. Sr2Fe2O5 contains alternating layers of FeO4 tetrahedra and FeO6 octahedra, whereas Ba2Fe2O5 comprises a complex array of FeO4 tetrahedra, FeO5 square-pyramids, and FeO6 octahedra. Here, we show that these structural differences lead to notable variations in magnetic properties, where Ba2Fe2O5 shows significantly higher magnetization compared to Sr2Fe2O5 in the entire temperature range, 2–400 K. More importantly, the differences in structural order lead to drastic variations in electrical conductivity. The room temperature electrical conductivity of Sr2Fe2O5 is about two orders of magnitude greater than that of Ba2Fe2O5. Variable temperature conductivity measurements in a wide temperature range, 25 °C–900 °C, reveal even more interesting differences between the two compounds. The conductivity of Ba2Fe2O5 remains nearly unchanged up to ∼400 °C, followed by a mild linear increase up to 900 °C. On the other hand, the conductivity of Sr2Fe2O5 shows a sharp increase above 200 °C, which continues up to ∼700 °C, followed by a plateau, i.e. saturation region, in the range 700 °C–900 °C.