Influence of annealing temperature on the microstructure and dielectric properties of ZnO nanoparticles

This work deals with structural and electrical investigations for different ZnO nanoparticles annealed at 300, 400 and 500 degrees C. The ac conductivity increases with temperature following the Arrhenius law, with single apparent activation energy for conduction process. The frequency dependence of the electric conductivity follows a simple power law behavior, in accord to the relation sigma(ac) (T, omega)=A(T)omega(s(T,omega)), where s is smaller than 1. Electrical conductivity measurements revealed semiconducting behavior and the variation of the universal exponent s with temperature designates the presence of correlated barrier hopping mechanism in these nano-materials. The impedance spectra were analyzed in terms of equivalent circuits involving resistors, capacitors and constant phase elements (CPE). The contribution of grain boundary resistance to the total resistance of the system is remarkable. The Nyquist diagrams of our nano-materials were used to identify an equivalent circuit and the fundamental parameters of the circuit are specific at different temperatures with the aim to study the contributions of the grains and boundary grains to the conductivity. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.