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 (DvO) 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 (DiH) and (DvH) 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 ~ 800 h 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. © 2016 Elsevier B.V. All rights reserved.