Oxygen permeability of mixed-conducting composite membranes: effects of phase interaction

Composite ceramic membranes, based on selected combinations of ionic conductors ((La0.9Sr0.1)(0.98)Ga0.8Mg0.2O3-delta-LSGM or Ce0.8Gd0.2O2-delta-CGO) and electronic/mixed conductors (La2Ni0.8Cu0.2O4+delta-LNC, La0.8Sr0.2Fe0.8Co0.2O3-delta-LSFC, La0.7Sr0.3MnO3-delta-LSM, and SrCoO3-delta-Sr2Fe3O6.5 +/-delta-SCSF), were processed and characterized aiming at the identification of key features to be considered in the design and optimization of materials performance as mixed conductors. Although after almost complete reaction between constituents, the best permeability was observed for the LSGM/LSFC combination processed under moderate firing conditions. Ceria-based composites, while preserving a typical composite microstructure, and suffering small compositional changes due to interaction between constituents, behaved always below the result of an ideal combination of the best characteristics of the individual components. Materials interaction, from modest compositional changes to formation of new phases, with deep changes in nominal composition, can be understood both as a challenge requiring proper identification of ideal processing conditions for phase preservation, but also as an opportunity for the development of entirely new composites and materials with compositional heterogeneities at grain size level.