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We investigated the effect of iron substitutions upon the structural, magnetic, electric, and dielectric properties in Pr0.7Ca0.3Mn1–xFexO3 mixed-valence manganite. The samples were synthesized using the solid-state reaction method and were analyzed by X-ray diffraction, magnetic and impedance spectroscopy measurements. X-ray diffraction analysis shows that all samples were found to be single phase and crystallize in the orthorhombic structure with Pnma space group. While the parent compound Pr0.7Ca0.3MnO3 exhibits a charge order sate, the substituted samples with low amount of iron exhibit a paramagnetic to ferromagnetic transition. However, the Curie temperature TC decreases with Fe content when we move from x = 0.02 to x = 0.1. From DC-conductance measurements, a typical semi-conducting behavior without any transition is observed for all investigated samples. Beyond a certain critical temperature noticed Tsat, the DC-conductance begins to saturate and reaches a maximum value. Then, the saturation temperature increases with increasing Fe content to attain Tsat = 260 K for x = 0.10. The correlated barrier hopping model was used to explain the frequency dependence of AC conductance. Impedance measurements confirm the contribution of the resistive grain boundary on the conduction mechanism. Then, it proves the existence of multiple electrical relaxation phenomena in the studied samples. The dielectric constant is found to be temperature dependent indicating that the compounds are polar dielectrics where the dipole orientation is governed by increasing temperature.

Pr0.65Ca0.25Cd0.1MnO3 ceramic was elaborated using the conventional solid-state reaction technique. The polycrystalline sample was subjected to investigate by ac impedance spectroscopy. From the main results, the electrical conductivity analysis confirms the semiconductor behavior and indicates that the hopping process governs the electrical conductivity. From ac-conductivity, two distinct mechanisms are observed. Indeed, the conduction mechanism is attributed to the correlated barrier hopping model in the middle of the frequency region and the overlapping large polaron tunneling in the high-frequency one. The analyzed impedance and modulus confirmed the presence of non-Debye-type relaxation phenomenon. Different electrical equivalent circuits were used to analyze the Nyquist plots. The obtained results confirm the contribution of grain boundary on the conduction. The increase in dielectric constant and the rate of its increase at low frequency were related to the disorder of the cation sublattices.

Impedance spectroscopy technique was used to characterize the electrical properties in a wide range of frequency [40–105 Hz] and temperature [80–700 K]. As a result, AC-conductivity spectrum follows the ‘double Jonscher Power Law’ in the temperature range [80–280 K], ‘Jonscher Power Law’ in [300–600 K] range and at 700 Kit is described by the classical Drude model. Moreover, the AC-conductivity analysis reveals the contribution of multiple mechanisms in conduction. In fact, the variation of the frequency exponent ‘s1’ with temperature shows that the correlated barrier hopping mechanism is the dominated model for conduction of charge carriers beyond T = 470 K. The previous model was observed again according to the temperature dependence of the frequency exponent ‘s2.’ Then, the deduced activation energy decreases with increasing frequency suggesting the availability of hopping conduction. The temperature dependence of AC-conductivity proves the existence of metal semi-conductor transition at 200 K. At high temperatures, the DC-conductivity analysis reveals that the conduction process is dominated by thermally activated hopping of small polaron. However, at low temperatures, it is confirmed that the most suitable mechanism for conduction is the Shklovskii–Efros-Variable Range Hopping process.

A Dy0.5(Sr0.95Ca0.05)0.5MnO3 system has been prepared by the sol gel method and sintered at temperatures of 700 °C and 1350 °C for a similar period of time. Its electrical and dielectrical data as a function of frequency and temperature have been recorded by means of impedance spectroscopy. It is observed that the contribution of grain boundary to total resistance becomes dominant once increasing sintering temperature. The increase of sintering temperature increases the static dielectric constant by 25 times. Such interesting result is understood in the framework of many reasons including the presence of oxygen vacancies. Unlike sample sintered at 700 °C , the compound sintered at 1350 °C reveals two extra relaxation processes. Further, the sample sintered at 1350 °C possesses the higher value of the dielectric constant as well as a lower value of the loss tangent, which makes it a promising candidate for technological applications. For transport properties, the conduction process is found to be governed by the band gap model.

Pechini sol-gel technique was used to prepare Mg0.6-xNixCo0.4Fe2O4 (x = 0 , 0.2, 0.4 and 0.6)-ferrite materials. Then, X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spectroscopy techniques are used to investigate the structural, morphological, electrical and dielectric properties. The X-ray diffraction patterns show that the prepared samples have a single phase. The SEM micrograph shows that the particle has an unchanging grain size distribution. Electrical measurements show that the DC conductivity is sensitive to temperature. Then, it is well noticed that the Mott and Davis law is governed by the small polaron hopping model. Also, impedance measurements show that the real part of impedance is extensively reduced when applying a voltage bias of $ V_{p}=10$ V. Such behavior can be related to the reduction of the available density of trapped charge. The results of Nyquist fitting are coherent with the electrical measurements according to which the sample with the highest DC conductivity possesses the lowest grain boundary resistance. Dielectric measurements confirm that the thermal evolution of the dielectric constant of the samples containing intermediary amounts of Ni (x = 0.2 and x = 0.4 is classical and show that the dielectric transition temperature is affected by polarization.

We have performed admittance spectroscopy measurements on a series of $Pr_{0.6}Sr_{0.3}Ca_{0.1}Mn_{1-x}Fe_{x}O_{3}$ (PSCMO) compounds with $ x=0$ , 0.025, 0.050 and 0.075. The results show that all samples exhibit a metal-insulator transition at a temperature which decreases with the iron content. The conduction mechanism is described by thermally activated hopping of small polaron. Activation energy changes at specific temperature T s, probably due to the contribution of the polarization effect to the conductivity. The dielectric permittivity increases with the temperature until a temperature T d near the specific temperature T s and then begins to decrease. This is explained by the fact that at a certain temperature, the free carriers acquire sufficient energy to overcome potential barriers, and so they enhance the conductivity and decrease the polarization. The dielectric permittivity measurements are well described by a modified Curie-Weiss law.