Effects of TiO2 addition on microstructure and ionic conductivity of gadolinia-doped ceria solid electrolyte

Abstract

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 (500–700ºC). One of the most utilized approaches to optimize the electrical conductivity and other properties of these materials is the introduction of a second additive, which could change the specific properties of cerium dioxide. Subsequently, in this work, ceria-20 mol% gadolinia with additions of TiO2 is prepared using solid state reaction. The main purpose is to investigate the effects of the additive on densification, microstructure and electrical conductivity of the solid electrolyte. Sintered pellets are characterized by evaluating apparent density, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and electrical conductivity by impedance spectroscopy. It was found that the small additions of titanium oxide improved the densification and turned negligible the porosity of sintered gadolinia-doped ceria specimens. This additive promotes increase of the blocking of charge carriers at the grain boundaries due to solute exsolution and formation of the pyrochlore Gd2Ti2O7 phase at grain boundaries for contents in excess of the solubility limit.