Impact of Ni Doping on the Structural, Optical, Electrical, and Dielectric Characteristics of ZnMn2O4 Spinel oxide

The Ni-doped ZnMn2O4 spinel was synthesized via a solid-state reaction method and evaluated for its potential electrochemical applications in energy storage systems. Structural analysis using XRD and Rietveld refinement confirmed a pure tetragonal phase with the I41/amd space group. SEM analysis was used to examine the morphology and particle size, while FTIR spectroscopy identified the characteristic metal–oxygen vibrations.
The optical band gap, determined from UV–visible spectroscopy (200–800 nm), was found to be 1.6 eV, showing a further decrease compared to the undoped sample. Impedance spectroscopy in the temperature range 323–473 K and frequency range 10-1–106 Hz revealed contributions from grains and grain boundaries. The temperature-dependent decrease in Nyquist semicircles indicates a thermally activated conduction mechanism. The AC conductivity follows the overlapping large polaron tunneling (OLPT) model.