Oxygen permeation performance of BaBiO_3-δ ceramic membranes

In this work, perovskite BaBiO_3-δ disk membranes were synthesized with the molar ratio (z) of BiO_1.5 to BaO between 0.5 and 3 at varying sintering temperatures. Disk membranes with z > 1.33, associated with a lower amount of Bi-rich perovskite phase, showed mechanically weak properties while membranes with z ≤ 1 showed superior stability at temperatures in excess of 800 °C. The best performance was obtained for the z = 0.86 disk membrane, reaching oxygen fluxes of 1.2 ml min^-1 cm^-2 at 950 °C. This was attributed to the higher sintering temperature and the formation of oxygen deficient phase of BaBiO_3-δ perovskite. For gas testing temperatures above 800 °C, it was found that the oxygen permeation was limited by both bulk diffusion and surface kinetics as oxygen flux did not increase proportionally to the inverse of membrane thickness reduction. Further analysis showed that the activation energy for oxygen ionic transport changed at 800 °C, however the z = 1 sample displayed the opposite trend from other compositions, indicating the formation of more oxygen vacancies in the crystal lattice. Mechanically stable disk membranes exposed to thermal cycling tests resulted in crystal structure instability of the pure perovskite (z = 1) and loss of oxygen vacancies while the z < 1 sample was relatively stable. Conversely, z > 1 sample showed superior thermal cycling and crystal structure stability.