Impedance Spectroscopic Analysis of Relaxation and Charge Transport in MnO₂-Doped Sodium–Zinc Phosphate Glasses

Sodium–zinc phosphate glasses with a fixed sodium oxide content were prepared with varying MnO₂ concentrations using the melt-quenching technique. The Davidson–Cole model was employed to analyze the distribution of relaxation times associated with the conduction mechanism over the temperature range 453–573 K and frequency range 100 Hz–5 MHz. Impedance, conductivity, electric modulus and dielectric constant were evaluated from the experimental data. The conductivity behavior was examined using the Cole–Cole and power-law models and the results were found to be mutually consistent. Grain and grain-boundary conductivities were determined by fitting the impedance spectra with constant phase elements (CPEs) in an equivalent circuit model. Nyquist plots of impedance and electric modulus confirmed the non-Debye relaxation behavior. The asymmetrical nature of the relaxation process was investigated using the Kohlrausch stretched exponent and shape parameters through the KWW and modified KWW models. The temperature-dependent power-law exponent (S) was observed to decrease with increasing temperature, indicating a correlated barrier hopping (CBH) mechanism for AC conductivity. Overall, the results demonstrate that the glasses exhibit semiconducting behavior, which is dependent on the manganese content in the glass matrix.