Assessment of thermochemically stable apatite La10(SiO4)6O3 as electrolyte for solid oxide fuel cells

Apatite-type lanthanum silicate with a formula of La10(SiO4)6O3 is a potential candidate electrolyte for SOFC system because of its high ionic conductivity and low activation energy. Pure La10(SiO4)6O3 powder was prepared by solid state reaction and using a suitable thermal pretreatment (1000 °C/5 h) of the as-purchased La2O3 powder. Materials characterization, thermal behaviors, and electrical properties of La10(SiO4)6O3 samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and two-point probe DC conductivity. A pure La10(SiO4)6O3 pellet was prepared at the sintering process of 1600 °C and 2.5 h with a high relative sintered density of 96.91%. The existence of secondary phases in La10(SiO4)6O3 pellet resulted in a lower conductivity than that of pure La10(SiO4)6O3 pellet. Eight-hour reduction-resistant stability tests under reducing atmosphere at the elevated temperature of pure La10(SiO4)6O3 prepared in this study shows a good thermochemical stability as compared to the well-developed 8 mol% Y2O3 stabilized ZrO2 (8YSZ).