Dynamic electric, dielectric, impedance, and modulus spectroscopy study with Rietveld refinement of Al-substituted NiCuZn bulk ceramics

Abstract

Ni_0.27Cu_0.10Zn_0.63Al_xFe_2−xO₄ (x = 0.0–0.16 with step 0.02) bulk ceramics were prepared from sol–gel-synthesized nanocrystalline powders and sintered at 1100 °C and 1250 °C, respectively. Rietveld refinements of the XRD data confirm the single-phase nature of the prepared ceramics with cubic spinel structure. Lattice parameter, cell volume, density, crystallite size, and grain size decrease with increasing Al content. The dynamic electrical and dielectric study has been carried out over 100 Hz to 100 MHz at room temperature (RT). The decreasing nature of ${\varepsilon}^{\ast}$ with a rising field shows the frequency-dependent regular dielectric behavior of the synthesized ceramics. The ${\varepsilon}^{\ast}$ magnitude increases several times with increasing sintering temperature due to elevated grain growth. The tan $\delta$ varies remarkably with Al content and explained with Koop’s phenomenological view of dielectrics. The lower tan $\delta$ magnitude (~ 0) reveals the high-frequency potentiality of the prepared ceramics. Electric modulus study ensures the non-Debye relaxation mode in each ceramic composition. The complex impedance spectra sketch the popular Cole–Cole plots and demonstrate the active contributions of grain and grain boundary resistances (R_g and R_gb) on electrical characteristics. Both the R_g and R_gb increase with Al substitution in many compositions reducing the eddy current losses and disperse more technological versatility for multifunctional appliances. The frequency-dependent conductivity obeys the Jonscher’s universal power law and presents three different conduction processes, long and short-range translational hopping as well as localized or re-orientational hopping motion at RT.