Dielectric relaxation behavior and overlapping large polaron tunneling conduction mechanism in NiO–PbO μ-cauliflower composites

Abstract

The NiO–PbO μ-cauliflower composites was synthesized via glycine assisted self-ignition techniques with an objective to investigate its temperature evolving distinct dielectric relaxor behavior and alternating current conduction mechanism, for exploring its application as high energy storage devices. The x-ray diffraction and Raman spectroscopy was utilized to characterize exquisite phase formation of the composites. The temperature dependent dielectric properties was performed in a broad range from 100 Hz to 1 MHz and it exhibits a diffuse phase transition in high temperature region. The Non-Debye type dielectric relaxation with grain and grain boundary contribution of different activation energy was confirmed by Nyquist plot (Z′−Z′′) of impedance spectra. Broad dielectric relaxation plateau was observed in the low temperature and high frequency region and electronic hopping motion with interfacial polarization is the underlying mechanism of it, instead of dipolar relaxation and internal barrier effect. The real ac conductivity was fitted by well-known Almond-west equation and the temperature dependent frequency exponent (S) confirmed double overlapping large polaron tunneling model (OLPT) model of electrical conduction mechanism from room temperature (298 K) to 533 K. The ac activation energies varries from 0.39 eV to 0.21 eV with high frequency dispersion and variable range hoppping (VRH) model is introduced to correlate the dc conductivity.