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This paper discusses the temperature and frequency-dependent dielectric and electrical transport properties of cobalt ferrite and its suitability for thermistor applications. The material is prepared through a high-temperature solid-state reaction route. The formation of the materials is checked by using an X-ray diffraction. Microstructure study is done through SEM analysis. Analysis of dielectric data shows a thermally activated relaxation process occuring in the material in the studied frequency range. Analysis of Nyquist plots at different temperatures reveal the contribution of grain to the overall electrical response of the compound. The variation of dc conductivity with temperature shows the NTCR behavior of the material. Looking into the strong dependence of resistivity on temperature, the thermistor parameters are evaluated using the grain resistance at different temperatures, which suggest the possible application for thermistor-based devices and as a temperature sensor. The temperature-dependent ac conductivity fits well with Jonscher’s universal power law. The activation energy calculated from the temperature-dependent spectroscopic plots of impedance and conductivity suggests the charge carriers involved in deciding transport properties.

Abstract:In the present research work, frequency dependent electrical properties of tungsten bronze structured compounds Na 2 Pb 2 R 2 W 2 Ti 4 Nb 4 O 30 (R = Nd, Sm) are reported. X-ray diffraction (XRD) study of polycrystalline ceramic samples confirms the formation of compounds with orthorhombic structure. Analysis of frequency dependent electrical data in the framework of modulus and conductivity formalism suggests the presence of thermally activated relaxation process in the compounds, which show Arrhenius behavior. The magnitudes of activation energies give the nature of the relaxing species. The real and imaginary parts of complex modulus trace the depressed semicircle in complex plane, suggesting non-Debye type relaxation process in the materials. The power law behavior of admittance data is successfully modeled by introducing constant phase element (CPE) to the equivalent circuit. A large value of power law parameter (n) of CPE below ferroelectric transition temperature (T c ) is attributed to the cooperative response of the dipoles which is reduced above T c . This behavior is correlated with the frequency dependence of CPE, suggesting a physical meaning to it. The frequency dependent AC conductivity at different temperatures follows Jonscher's universal power law. Almond and West formalism is used to estimate the hopping rate, activation enthalpy and charge carrier concentration in the materials.