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

摘要

A CoCO_3 added Pb((Zn_(1/3)Nb_(2/3))_(0.20)(Zr_(0.50)Ti_(0.50))_(0.80))O_3 (0.2PZN-0.8PZT + xCoCO_3) system has been prepared and investigated. The tetragonal distortion c/a of specimens increases abruptly with increasing CoCO_3 content, but is almost constant for x ≥ 0.2 wt%, confirming that the solubility limit of CoCO_3 in 0.2PZN-0.8PZT is about x = 0.2 wt%. Complex impedance spectroscopic analysis, in the temperature range of 250-300 ℃ 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 CoCO_3 doping 0.2PZN-0.8PZT, both the single and double ionized oxygen-vacancies contribute to the conduction process.