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Two samples of ZnxMn1−xFe2O4 (x = 0, sample A; and x = 0.4, sample B) were synthesized by the hydrothermal method. From complex impedance measurements in the range 100 Hz–2 MHz and for temperatures T between 30 and 130 °C, the barrier energy between localized states ΔErelax was determined for the first time in these samples. For sample B, a single value of ΔErelax was highlighted (0.221 eV), whilst, for sample A, two values were obtained (0.012 eV and 0.283 eV, below 85 °C and above 85 °C, respectively), associated with two zones of different conductivities. Using the Mott's VRH model and the CBH model, we determined for the first time both the bandgap energy barrier (Wm) and the hopping (crossover) frequency (ωh), at various temperatures. The results show that, for sample A, Wm has a maximum equal to 0.72 eV at a temperature between 70 and 80 °C, whilst, for sample B, Wm has a minimum equal to 0.28 eV at a temperature of 60 °C, the results being in good agreement with the temperature dependence of the static conductivity σDC(T) of the samples. By evaluating σDC and eliminating the conduction losses, we identified, using a novel approach, a dielectric relaxation phenomenon in the samples, characterized by the activation energy EA,rel. At various temperatures, we determined EA,rel, which ranged from 0.195 eV to 0.77 eV. These results are important, as understanding these electrical properties is crucial to various applications, especially in technologies where temperature variation is significant. [ABSTRACT FROM AUTHOR]

Ultrasound-assisted co-precipitation method is used for the first time to prepare F e 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. [ABSTRACT FROM AUTHOR]