Abstract
Sodium and silicon co-doped NiO (NSNO) of the formula NaxSiyNi1-x-yO (x = 0.05, 0.1 and y = 0.02, 0.05) were prepared by solid state reaction. Structural, electrical conduction and dielectric properties of the NSNO ceramics were investigated. The current NSNO ceramics exhibited giant dielectric constant (epsilon' similar to 10(4) at 1.1 KHz and 300 K) and three dielectric relaxation peaks were found on the curve of the frequency dependence of the imaginary part of electric modulus M '' The complex impedance diagrams showed three electrical responses, which have been attributed to the domain, domain-boundaries and grain-boundaries in the NSNO ceramics. Analysis of the temperature dependence of the conductivity for the current ceramics indicated that the electrical conduction mechanism changes from variable range hoping at low temperatures (T < 220 K) to nearest neighbor hopping mechanism at higher temperatures. The electrically heterogeneous structure, revealed by the complex impedance analysis, combined with considerable polarization due to defect dipoles are thought to be the cause for the giant dielectric response of NSNO ceramics.