PHASE INTERACTION AND DISTRIBUTION IN MIXED IONIC ELECTRONIC CONDUCTING CERIA-SPINEL COMPOSITES

Mixed Ionic electronic conductors find various applications as SOFC cathodes and oxygen transport membranes. Dual phase composites are a promising class of thermochemical stable materials, in which two ceramic phases are coupled to provide a pure electronic and ionic conducting pathway, respectively. Composites of 20 mol% Gadolinia doped ceria (GDC) and FeCo2O4 spinel (FCO) are investigated. GDC-FCO 60:40 wt-% ratio showed reasonable oxygen permeation with ionic conductivity as the limiting factor. Starting from this composition, spinel content was stepwise reduced to as low as 10 wt-% in the composite and their corresponding electrical conductivity and oxygen permeation were measured from which ambipolar conductivity was calculated. GDC-FCO 85:15 wt-% ratio shows the highest amhipolar conductivity comparable to standard single phase La0.58Sr0.4Fe0.8Co0.2O3-delta (LSCF) at 850 degrees C. The Microstructure analysis showed reversible and thus temporary spinel decomposition at sintering temperature as well as phase interaction forming a Gd- and Fe-rich orthorhombic perovskite with traces of Ce and Co. To further investigate the phase interaction and secondary phase formation, Pulsed Layer Deposition of FCO layer (similar to 400 nm) on a polycrystalline GDC substrate and annealing at varying temperatures and times from 1000 to 1200 degrees C were carried out. These samples were analyzed by XRD, STEM, and SIMS to understand the intertayer interaction of the phases.