Temperature dependent charge transport and conduction mechanism through different electroactive regions in NiO-ZnO heterostructure nanocomposite by using impedance spectroscopy

This work reports rods and flakes like NiO-ZnO heterostructure composite, having a crystallite size of 38 (±2) nm prepared via hydrothermal route. The structural, optical, and dielectric characteristics of NiO-ZnO heterostructure composite are explored using XRD, TEM, FESEM, UV-DRS, and impedance spectroscopy techniques. The refined XRD spectrum indicates the presence of multi phases present in NiO-ZnO heterostructure composite. The complex impedance spectroscopy performed through a wide temperature range (313 K–393 K) in the frequency range of (1 Hz–10 MHz). The complex impedance spectroscopy directs the contribution of grain and interface resistance of electro active regions. The Nyquist plane plots highlight temperature based non-Debye relaxation conduction mechanism. With the increase in temperature resistance of the material decreases 3.8 × 10⁵–2.6 × 10⁴ Ω meanwhile conductivity got improved from 1.05 × 10⁻⁶ to 4.25 × 10⁻⁶ Ωcm⁻¹. The adiabatic small polaronic hopping model is applied to estimated activation energies associated with charge carriers Ni⁺² (0.46 eV) and Zn⁺² (0.48 eV). The Jonscher's power law fitted over ac conductivity to estimate physical parameters, i.e. binding energy, hopping length, barrier height etc. The optical band gap (E_g) decreases due to Ni⁺² content in the ZnO matrix and a blue shift of band gap is observed using UV-DRS. So it is worth mentioning that this temperature dependent dielectric, impedance, and transport characteristics of NiO-ZnO heterostructure showed outstanding properties for emerging energy applications.