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

Abstract In this work, Sr 2 + and Y 3 + co-doped BaCeO 3 -based perovskite Ba 0.9 Sr 0.1 Ce 0.85 Y 0.15 O 3 − 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 ( p O 2 ) and water vapor pressure ( p H 2 O). During oxidation/reduction process, the electrical conductivity showed a monotonic relaxation behavior and in − 2.65 ≤ log( p O 2 /atm) ≤ − 0.67 range the values of oxygen chemical diffusivity ( D ˜ vO ) and surface exchange coefficient ( κ vO ) varied in 10 − 6 –10 − 4 cm 2  ⋅ 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 cm 2  ⋅ s − 1 range, respectively, whereas hydrogen and oxygen surface exchange coefficient ( κ iH ) and ( κ vH ) 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 BaCe 0.85 Y 0.15 O 3 − 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.