The electrical conductivity of Fe3(PO4)2·8H2O materials

Abstract

Ultrasound-assisted co-precipitation method is used for the first time to prepare $$Fe_{3}^{2 + }$$ (PO4)2·8H2O polycrystalline materials which crystallise at room temperature in a monoclinic structure (C2/m space group). The frequency and temperature dependence of the electrical conductivity σ of the Fe3(PO4)2·8H2O sample was determined, and they follow Jonscher’s law. The results show that, in the low frequency range (below 10 kHz), the conduction mechanism can be explained by the Mott’s variable-range-hopping model; a change of slope of the conductivity is observed at ≈ 110 °C, which may be associated with a change in the crystal structure, due to the loss of water molecules from the sample. Based on Mott’s model, the density of localized states near the Fermi level, N(EF), the hopping distance, R, and the hopping energy, W, were computed. The results show that, at a constant frequency (below 10 kHz), N(EF) does not depend on temperature, while R decreases and W increases with the increase in temperature. Over 200 kHz, the correlated barrier hopping model is characteristic to the conductivity for this type of materials and the calculated band gap energy is 1.072 eV, in the (25–110) °C range and 0.821 eV, in the (110–220) °C range.