Crystallization and electrochemical performance of La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ)- Ce_(0.8)Gd_(0.2)O_(1.9) thin film cathodes processed by single solution spray pyrolysis

摘要

La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3 - δ)-Ce_(0.8)Gd_(0.2)O_(1.9) (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 °C. Films annealed at 600 °C contained a mixture of amorphous regions and crystalline regions composed of fine crystallites (< 5 nm). Annealing above 600 °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 °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 °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.