Impact of Cr-poisoning on the conductivity of LaNi_(0.6)Fe_(0.4)O_3

摘要

This study demonstrates the significant impact of Cr on the electronic conductivity of a LaNi_(0.6)Fe_(0.4)O_3 (LNF) porous cathode layer at 800 °C. Vapor transport of Cr-species, originating from a porous metallic foam, and subsequent reaction with LNF, results in a decrease of the electronic conductivity of the LNF-layer. Cr has been detected throughout the entire cross-section of a 16μm thick LNF layer, while Ni, besides its compositional distribution in the LNF layer, has also been found in enriched spots forming Ni-rich metal oxide crystals. Transmission electron microscopy revealed that Cr is gradually incorporated into the LNF-grains, while Ni is proportionally expelled. Electron diffraction performed in the center of a sliced grain showed the initial rhombohedral crystal structure of LNF, whereas diffraction performed close to the edge of the grain revealed the orthorhombic perovskite crystal structure, indicating a Cr-enriched perovskite phase. Progressive Cr deposition and penetration into the LNF grains and necks explains the electronic conductivity deterioration. The impact of Cr-poisoning on the electronic conductivity of the LNF porous layer is considerably smaller at 600 C than at 800 C.