Influence of impurities on the bulk and grain-boundary conductivity of CaZrO3-based proton-conducting electrolyte: A distribution of relaxation time study

In the present work single-phase proton-conducting electrolyte CaZr0.95Sc0.05O3-delta (CZS) is synthesized by a conventional solid-state technique with different impurities content. Impurities are introduced by using different milling bodies during the synthesis. It is shown that milling by steel balls or grinding in a jasper mortar results in approximately 1 at.% of iron and silica respectively. Milling with ZrO2 balls does not lead to a noticeable increase in the level of impurities in CZS. The influence of impurities on the bulk and grain boundary conductivity is studied by means of electrochemical impedance spectroscopy. The measurements are performed on symmetric cells with different electrodes: Pt vertical bar CZS vertical bar Pt, (Pt + PrO2)vertical bar CZS vertical bar(Pt + PrO2) and Ag vertical bar CZS vertical bar Ag. The data analyzed by the conventional equivalent circuit and distribution of relaxation times (DRT) techniques. It is shown that impurities influence only the grain boundary conductivity which proves that the grain boundary segregation occurs. However, a large grain-boundary resistance could be an obstacle to determine the bulk resistance. (C) 2020 Elsevier Ltd. All rights reserved.