Structural, optical and NTCR properties of Ca doped ZnO ceramics

Calcium doped zinc oxide (Zn 1− x Ca x O, x = 0–0.03) ceramics has been synthesized by solid state reaction method. The phase, band gap, negative temperature co-efficient of resistance (NTCR) properties were determined by X-ray diffraction, diffuse reflectance spectroscopy (DRS) and impedance spectroscopy. The synthesized samples are of single phase. All structural parameters were evaluated using Rietveld refinement method. Dielectric and impedance properties of the synthesized sample have been investigated with different dopant concentration, temperature and frequency. Doping decreases the dielectric constant of ZnO and the Ca doped sample shows drastic low value of dielectric constant. Peak was observed in dielectric loss spectra of Ca doped ZnO sample. The impedance study shows the NTCR behaviour and a temperature dependence of electrical relaxation phenomena at higher temperature. The band gap of ZnO decreases, whereas Urbach energy increases with doping.