EFFECTS OF TiO_2 ADDITION ON MICROSTRUCTURE AND IONIC CONDUCTIVITY OF GADOLINIA-DOPED CERIA SOLID ELECTROLYTE

摘要

Ceria containing trivalent rare-earth is a solid electrolyte with higher ionic conductivity than the yttria fully-stabilized zirconia standard ionic conductor. This feature turns these ceria-based ionic conductors promising materials for application in solid oxide fuel cells operating at intermediate temperatures (500-700°C). One of the most utilized approaches to optimize the electrical conductivity and other properties of these materials is the introduction of a second additive. In this work, ceria-20 mol% gadolinia with additions of TiO_2 was prepared by solid state reaction. The main purpose was to investigate the effects of the additive on densification, microstructure and electrical conductivity of the solid electrolyte. Sintered pellets were characterized by evaluating apparent density, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and electrical conductivity by impedance spectroscopy. The additive was found to influence all studied properties. Increase of densification was obtained with TiO_2 addition. This additive promotes increase of the blocking of charge carriers at the grain boundaries due to solute exsolution and formation of the pyrochlore Gd_2Ti_2O_7 phase at grain boundaries for contents in excess of the solubility limit.