On the structural and electrical properties of MgFe2O4, MgMn0.2Fe1.8O4, and Mn3O4
Farshad Farshidfar, M Lapolla, Arash Fattahi, Khashayar Ghandi
Abstract
Charge carrier transport via donor/acceptor pairs of similar elements is dominant in n-type MgFe 2 O 4 and p-type Mn 3 O 4 spinels. The temperature-independent activation energy in the form of the nearest neighbor hopping model is applied for Fe 2+ /Fe 3+ pairs of cubic MgFe 2 O 4 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 Mn 3 O 4 , 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 MgFe 2 O 4 , 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.