Effects of cobalt doping on the microstructure, complex impedance and activation energy in 0.2PZN–0.8PZT ceramics

A CoCO3 added Pb((Zn1/3Nb2/3)0.20(Zr0.50Ti0.50)0.80)O3 (0.2PZN–0.8PZT + xCoCO3) system has been prepared and investigated. The tetragonal distortion c/a of specimens increases abruptly with increasing CoCO3 content, but is almost constant for x ≥ 0.2 wt%, confirming that the solubility limit of CoCO3 in 0.2PZN–0.8PZT is about x = 0.2 wt%. Complex impedance spectroscopic analysis, in the temperature range of 250–300 °C from 1 mHz to 10 MHz, provides another evidence that 0.2 wt% is indeed the solubility limit. Both spectroscopic peaks of Z″ and M″ vs frequency are observed in the similar frequency region, indicating the approximated-Debye behavior in the studied systems. Temperature dependent bulk relaxation values are found to obey linear-Arrhenius fit. Based on the activation energy values, it can be concluded that in CoCO3 doping 0.2PZN–0.8PZT, both the single and double ionized oxygen-vacancies contribute to the conduction process.

► Both XRD and complex impedance spectrum confirmed 0.2 wt% is the solubility limit.
► The approximated-Debye behavior existed in the studied systems.
► Single and double ionized oxygen vacancy contribute to the conduction process.