Modulus Spectroscopy and ac Conductivity of Zn1−xCaxO Ceramics

Abstract

Ca doped ZnO (Zn1−xCaxO, x = 0,0.01 and 0.02) ceramics were synthesized by simple solid state reaction route. Structural characterization was carried out by X-ray diffraction (XRD) technique. The modulus and ac conductivity of the synthesized ceramics were analyzed by an impedance analyzer. The chemical composition of the synthesized ceramics was confirmed by EDX. The analysis of the XRD peaks revealed the hexagonal wurtzite structure, P63 mc space group for all compositions. The absence of extra peaks in the diffraction patterns indicate that the synthesized ceramics are in single phase. The crystallite size of ZnO decreases with Ca doping and also with increasing concentration of Ca. EDX analysis shows the presence of Ca in ZnO lattice. The frequency dependence imaginary part of modulus suggests the temperature dependent relaxation phenomena in the synthesized ceramics. The sign of long range to short range transition of charge carriers was observed in Ca doped ZnO ceramics. Increase in Ca concentration enhances the capacitance value of the ceramics. The asymmetric peak broadening in modulus predicts a non-Debye type of relaxation mechanism. The modulus studies also confirm the single phase formation of the synthesized ceramics. The ac conductivity increases with increase in frequency and temperature for all samples showing their semiconducting nature. The data of conductivity also shows the NTCR behavior. Again the ac conductivity decreases with Ca doping which may be due to the introduction of defects created by Ca2+ ion in ZnO system.