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

• Published in: Ceramics international Vol. 47; no. 17; pp. 24732 - 24742
• Main Authors: Essalah, G., Leroy, G., Carru, J.C., Duponchel, B., Mascot, M., Poupin, Ch, Cousin, R., Guermazi, S., Guermazi, H.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-09-2021; Elsevier
• Subjects: Catalysis; Chemical Sciences; Composite; Conduction mechanisms; Dipolar relaxation; MWS; Semiconductor-metal transition; Semiconductor-metal transition; MWS; Conduction mechanisms; Composite; Dipolar relaxation
• ISSN: 0272-8842; 1873-3956
• DOI: 10.1016/j.ceramint.2021.05.196

This paper deals with the study of the physical properties of ZnO/ZnNb2O6/Nb2O5 composite. X-ray diffraction (XRD) proves the coexistence of hexagonal ZnO, tetragonal Nb2O5 and orthorhombic ZnNb2O6. 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: Ea ~ 0.53eV in the interval 150 °C < T < 275 °C, and Ea ~ −0.47eV for T > 275 °C. Moreover, the permittivity variations show the existence of interfacial Maxwell-Wagner-Sillars (MWS) and dipolar polarization.