Role of chromium: Iron ratio and oxygen partial pressure on the processing and chemical stability of iron doped lanthanum strontium chromite based OTM

The present research, as a part of the OTM materials development and testing effort, examines the combined effect of the Cr: Fe ratio (7:3, 8:2 and 9:1) and oxygen partial pressure (PO2) on the densification, microstructural development, and chemical stability of lanthanum chromite (La0.8Sr0.2)0.95Cr1-xFexO3 (LSCrF) for application in oxygen transport membrane and solid oxide fuel cell electrode. While highest density of 96.3 (±0.5) % is achieved for LSCrF with Cr: Fe ratio of 7:3 at 1400 °C and PO2 ∼ 10−10 atm., the relative density decreases with increase in Cr: Fe ratio and PO2. LSCrF perovskite stability increases with increase in Cr: Fe ratio in reducing gas atmosphere. LSCrF (7:3) dissociates into FeOx and Fe1+xCr2-xO4 under reducing gas atmosphere (Ar-3%H2-3%H2O). LSCrF (9:1) perovskite does not show any evidence of second phase (FeOx and Fe1+xCr2-xO4) formation with decrease in PO2 unlike LSCrF (7:3 and 8:2). Defect chemistry and mechanism for FeOx and Fe1+x Cr2−x O4 formation in reducing atmosphere is described. LSCrF decomposition and the formation of the secondary phases are in agreement with the thermodynamic simulation results obtained with the La-Sr-Cr-Fe-O thermodynamic database.