Oxide ion and electron transport properties in lanthanum silicate oxyapatite ceramics

An oxygen-excess-type lanthanum silicate (LSO) solid electrolyte with high chemical stability as well as high ion conductivity was developed by optimizing the chemical composition, La 9.333 + x (Si 6 − y Al y )O 26 + 1.5 x − 0.5 y . It was found that La 10 (Si 5.8 Al 0.2 )O 26.9 ( x = 0.667, y = 0.2) exhibited the highest conductivity among them, and addition of a small amount of iron was effective for the improvement of its chemical stability. The LSO specimen of x = 0.667 and y = 0.2 with iron addition (0.5 mol%) was chemically stable and had a conductivity of 5.6 × 10 − 2 S cm − 1 under air at 1073 K, while its electronic conductivity was less than 2.0 × 10 − 4 S cm − 1 at the same temperature. The oxygen tracer diffusion coefficient, D O * of this material was determined as 2.0 × 10 − 8 cm 2 s − 1 at 1073 K.