Dielectric behavior and ac electrical conductivity of nanocrystalline nickel aluminate

Nanocrystalline nickel aluminate was prepared by chemical co-precipitation, and nanoparticles having different particle size were obtained by annealing the precursor at different temperatures. The TG/DTA measurements showed thermal decomposition was a three-step process with crystallisation of the spinel phase started at a temperature 420 °C. The X-ray diffraction analysis confirmed that the specimen began to crystallise on annealing above 420 °C and became almost crystalline at about 900 °C. The particle sizes were calculated from XRD. Dielectric properties of nickel aluminate were studied as a function of the frequency of the applied ac signal at different temperatures. It was seen the real dielectric constant ɛ′, and dielectric loss tan δ decreased with frequency of applied field while the ac conductivity increased as the frequency of the applied field increased. The dielectric relaxation mechanism is explained by considering nanostructured NiAl2O4 as a carrier-dominated dielectric with high density of hopping charge carriers. The variation of ɛ′ with different particle size depends on several interfacial region parameters, which change with the average particle size.