Study of mass transport kinetics in co-doped Ba0.9Sr0.1Ce0.85Y0.15O3 − δ by electrical conductivity relaxation

Abstract

In this work, Sr2+ and Y3+ co-doped BaCeO3-based perovskite Ba0.9Sr0.1Ce0.85Y0.15O3−δ (BSCY) was synthesized by solid-state reaction method, and its mass transport behavior was studied using electrical conductivity relaxation (ECR) measurements in 600–800°C range with respect to variations in oxygen partial pressure (pO2) and water vapor pressure (pH2O). During oxidation/reduction process, the electrical conductivity showed a monotonic relaxation behavior and in −2.65≤log(pO2/atm)≤−0.67 range the values of oxygen chemical diffusivity (D˜vO) and surface exchange coefficient (κvO) varied in 10−6–10−4 cm2⋅s−1 and 10−4–10−2 cm⋅s−1 range, respectively. However, during hydration/dehydration process, the electrical conductivity showed a non-monotonic twofold relaxation behavior, and hydrogen, and oxygen chemical diffusivities (D˜iH) and (D˜vH) values were in 10−5–10−3 and 10−6–10−4 cm2⋅s−1 range, respectively, whereas hydrogen and oxygen surface exchange coefficient (κiH) and (κvH) values were in 10−3–10−2 and ~10−4–10−2 cm⋅s−1 range, respectively. The comparison of H and O diffusivities of BSCY with BaCe0.85Y0.15O3−δ (BCY) showed that during hydration/dehydration the diffusivities of BSCY were lower than that of BCY. The long-term electrical conductivity measurement for ~800h in humidified conditions showed a gradual decrease, which might be due to the gradual appearance of rhombohedral phase in otherwise orthorhombic BSCY, as confirmed by the X-ray diffraction (XRD) measurements.