AC conductivity, dielectric and electrical modulus studies of bulk Zn0.95Co0.05O ceramic

Polycrystalline Zn 0.95 Co 0.05 O bulk sample was prepared by using a sol–gel method. The temperature dependence and frequency dependence of AC conductivity, dielectric and electrical modulus of bulk Zn 0.95 Co 0.05 O in a pellet form were investigated in the temperature range of 300–500 K and frequency range of 1 kHz–1.5 MHz. While the real values of dielectric constant ( ε' ) increased with increasing temperature, they decreased with increasing frequency. Its calculated values for 300 K ranged from 30.65 to 11.24 in the frequency range from 1 kHz to 1 MHz. The density of localized states N(E f ) values near the Fermi level were obtained in the order of 5.21 × 10 35 –5.39 × 10 36 eV −1 m −3 for the studied frequency and temperature range. The maximum barrier height W m value was found to be 0.132 eV. The variation of AC conductivity with temperature showed a semiconductor behavior. We observed that second semicircle started to form in the graph of the real and imaginary parts of the modulus. It can show that two separate conduction processes caused by grain and grain boundary. The maximum frequency values of the imaginary part of the modulus were different indicating a non-Debye type of relaxation process. Also, the non-coincidence of peaks corresponding to the frequency dependence of impedance and modulus confirmed deviation from Debye-type relaxation for the Zn 0.95 Co 0.05 O sample. The average value of the activation energy calculated from the modulus was 0.499 eV. The activation energy values calculated from the AC conductivity decreased as the frequency increased and its values varied between 0.54 eV and 0.42 eV. These activation energy values of the sample are very similar, suggesting that the relaxation process may refer to the same type of charge carriers.