Conduction mechanisms and relaxation phenomena along with electronic transition of ZnO/ZnNb2O6/Nb2O5 composite.

This paper deals with the study of the physical properties of ZnO/ZnNb 2 O 6 /Nb 2 O 5 composite. X-ray diffraction (XRD) proves the coexistence of hexagonal ZnO, tetragonal Nb 2 O 5 and orthorhombic ZnNb 2 O 6. Scanning electron microscopy (SEM) observations reveals heterogenic distribution of grains with average size of about 456 nm. The dielectric measurements are performed in 20 Hz–1MHz frequency range between 150 °C and 350 °C. Theoretical fit demonstrates that the electric resistivity, associated to grains and grain boundaries, decreases as a function of temperature up to 275 °C. At 275 °C, the composite presents a semiconductor-metal transition, confirmed by the temperature-dependence of DC conductivity. Moreover, the AC conductivity variations suggest that the AC conduction mechanisms are explained by the Quantum-Mechanical Tunneling (QMT) model below 275 °C and the Non-Overlapping Small Polaron Tunneling (NSPT) one above 275 °C. Also, the activation energies, related to dielectric relaxation processes and DC conductivity, are almost equal: E a ~ 0.53eV in the interval 150 °C < T < 275 °C, and E a ~ −0.47eV for T > 275 °C. Moreover, the permittivity variations show the existence of interfacial Maxwell-Wagner-Sillars (MWS) and dipolar polarization. [ABSTRACT FROM AUTHOR]