A CoCO3 added Pb((Zn1/3Nb2/3)(0.20)(Zr0.30Ti0.50)(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 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 degrees 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. (C) 2012 Elsevier B.V. All rights reserved.