Experimental evidence of hydrogen-oxygen decoupled diffusion into BaZr0.6Ce0.25Y0.15O3-δ

The electrical properties of BaZr0.6Ce0.25Y0.15O3-delta (BZCY) were studied as a function of both oxygen partial pressure (-2.65 <= log(P-O2 atm(-1)) <= -0.62) and water vapor activity (-3.33 <= log(P-H2O atm(-1) <= -1.3)) in the temperature range of 973-1073 K. The total conductivity slightly increased in reducing atmospheres with increasing water vapor activity because of the relative contribution to the total conductivity by the redox reaction at the given thermodynamic conditions. The partial conductivities of protons, holes and oxygen vacancies were successfully calculated, and the activation energy determined for proton transport was 0.3+/-0.1 eV. The chemical diffusivity of oxygen at a fixed water vapor activity, (D) over tilde (vO), could only be evaluated from Fick's second law during oxidation and reduction at the fixed water vapor activity. However, twofold nonmonotonic conductivity relaxation behaviors were clearly confirmed in the temperature range investigated during hydration/dehydration. If P-O2 represents the fixed oxygen partial pressure, (D) over tilde (iH) is the hydrogen chemical diffusivity at P-O2 and (D) over tilde (vH) is the oxygen chemical diffusivity at P-O2, it was observed that (D) over tilde (iH) > (D) over tilde (vH) at all experimental conditions, suggesting that the hydrogen chemical diffusion is always faster than oxygen on hydration/dehydration in the temperature range studied. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.