Temperature dependence anomalous dielectric relaxation in Co doped ZnO nanoparticles

Abstract

We have reported temperature and frequency dependence of dielectric behavior of nanocrystalline Zn1−xCoxO (x=0.0, 0.01, 0.05 and 0.1) samples prepared by gel-combustion method. The synthesized samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and LCR-meter, respectively. The XRD analysis reveals that ZnO has a hexagonal (wurtzite) crystal structure. The morphology and size of the nanoparticles (∼10–25nm) were observed by SEM for 5% Co doped ZnO sample. In dielectric properties, complex permittivity (ɛ*=ɛ′−jɛ″), loss tangent (tanδ) and ac conductivity (σac) in the frequency range 75kHz to 5MHz were analyzed with temperature range 150–400°C. The experimental results indicate that ɛ′, ɛ″, tanδ and σac decreases with increase in frequency and temperature. The transition temperature as obtained in dispersion curve of dielectric constant shifts toward higher temperature with increase Co content.