On the structural and electrical properties of MgFe₂O₄, MgMn_0.2Fe_1.8O₄, and Mn₃O₄

Charge carrier transport via donor/acceptor pairs of similar elements is dominant in n-type MgFe₂O₄ and p-type Mn₃O₄ spinels. The temperature-independent activation energy in the form of the nearest neighbor hopping model is applied for Fe²⁺/Fe³⁺ pairs of cubic MgFe₂O₄ spinel in the temperature range of 423-523 K (150-250 °C). At such high temperatures, even for this relatively narrow temperature range, the constant energy barrier deviates to a variable range hopping energy barrier in the case of Mn₃O₄, due to Jahn-Teller active octahedral sites. Replacing 10 mol% of Fe at octahedral sites with Mn has significantly increased the electron hopping energy barrier and electrical conductivity of MgFe₂O₄, while keeping the nearest neighbor hopping model dominant. The observed high energy barrier is due to donor/acceptor pairs of different elements (Mn/Fe). Due to a lack of structural distortion, deviation from the nearest neighbor hopping mechanism with temperature-independent activation energy was not observed. Rietveld refined XRD patterns and FT-IR spectra are utilized to support the argument on electrical conductivity mechanisms.