Temperature dependence anomalous dielectric relaxation in Co doped ZnO nanoparticles

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 (∼10–25 nm) were observed by SEM for 5% Co doped ZnO sample. In dielectric properties, complex permittivity (ɛ* = ɛ′ − jɛ″), loss tangent (tan δ) and ac conductivity (σac) in the frequency range 75 kHz to 5 MHz were analyzed with temperature range 150–400 °C. The experimental results indicate that ɛ′, ɛ″, tan δ 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.