Plasma Spray-Physical Vapor Deposition of La1-xSrxCoyFe1-yO3-d Oxygen Transport Membranes on Porous Metallic Supports: Controlling Stress State and Phase Composition

La_0.58Sr_0.4Co_0.2Fe_0.8O_3-δ, deposited on a metallic porous support by means Plasma Spray-Physical Vapor Deposition (PS-PVD) is a promising candidate for oxygen-permeation membranes. However, after O₂ permeation tests, membranes show vertical cracks leading to leakage. In this work, a feature leading to crack formation has been identified. Specifically:  Membrane residual stress changes during thermal loading are found to be related to a phase transformation in the support. In order to improve membrane performance; the support has been optimized by applying an appropriate heat treatment. Additionally, it has been found that coatings deposited at lower oxygen partial pressures consist of 75% cubic and 25% orthorhombic phases probably in a non-equilibrium state due to fast quenching during spraying. Due to non-stoichiometry, which drives formation of non-perovskite phases during annealing, membrane stability and ionic conductivity are affected. The oxygen amount used during spraying can be used to suppress the cubic to tetragonal phase transformation.