The influence of NiO, used as a sintering aid, on the transport properties of BaZr0.8Y0.2O3-Delta was investigated by monitoring electrical conductivity relaxation of specimens with and without NiO during hydration in atmospheres of different oxygen activities at 700 and 800 degrees C. The chemical diffusivities of H and O governing the kinetics were precisely evaluated from the transient conductivity, and all the defect-chemical parameters the two external equilibrium constants and mobilities of all the carriers, V-o(center dot), H-i and h(center dot) - were determined from the steady-state equilibrium conductivity. It is found that the processing benefits afforded by NiO are accompanied by a significant reduction in ionic mobilities and hydration reaction constant. These factors, in turn, result in a smaller electrolytic regime in the presence of NiO than when it is absent. (C) 2015 Elsevier B.V. All rights reserved.