Crystallization and electrochemical performance of La0.6Sr0.4Co0.2Fe0.8O3-delta-Ce0.8Gd0.2O1.9 thin film cathodes processed by single solution spray pyrolysis

La0.6Sr0.4Co0.2Fe0.8O3-delta-Ce0.8Gd0.2O1.9 (LSCF-CGO) thin films obtained by spray pyrolysis of a single precursor solution were investigated by XRD, TEM and impedance spectroscopy at annealing temperatures ranging from 500 to 900 degrees C. Films annealed at 600 degrees C contained a mixture of amorphous regions and crystalline regions composed of fine crystallites (nm). Annealing above 600 degrees C increased the ratio of crystalline to amorphous material, led to the segregation of the films into distinct LSCF and CGO phases, and promoted grain growth. The electrical behavior of the films depended on annealing temperature. At testing temperatures of 400 degrees C and below, the polarization resistance of films with lower annealing temperatures was larger than the polarization resistance of films with higher annealing temperatures. However, at testing temperatures of 500 degrees C and above the polarization resistance of films with lower annealing temperatures was equal to or lower than the polarization resistance of films with higher annealing temperatures. This was reflected by the activation energy that decreased with increasing annealing temperature. The varying electrical behavior may be related to microstructural changes that caused bulk diffusion to be the rate-limiting step in films with lower annealing temperatures and oxygen dissociation to be the rate-limiting step in films with higher annealing temperatures. (C) 2011 Elsevier B.V. All rights reserved