The phase stability and electrical conductivity of a proton-conducting oxide, Ba(Zr0.84Y0.15Cu0.01)O3-delta (BZYCu), sintered under various atmospheres was systematically investigated. The partial pressures of oxygen (Po-2) and barium (P-Ba) were used as the tunable experimental parameters to control the surrounding atmosphere during sintering. According to the analysis, the potentially volatile species BaCO3, formed by the decomposition of BZYCu under a CO2-containing atmosphere at around 600 degrees C, was found to induce barium losses by evaporation. These barium losses, and the associated Y2O3 segregation, were the decisive factor in determining the phase stability and electrical conductivity of the resulting BZYCu; both of these properties deteriorated with barium evaporation. Maintaining the optimum balance of Po-2, and P-Ba during sintering is crucial for minimizing Y2O3 segregation by kinetically suppressing the volatilization of barium. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.