Lanthanum gallate-based sintered body, manufacturing method thereof, and solid oxide fuel cell using the same as solid electrolyte

A lanthanum gallate-based sintered body comprises a base material formed of lanthanum gallate-based oxide, and grains having a KNiFstructure and/or grains having a layered perovskite structure are dispersed into the base material. Consequently, the lanthanum gallate-based sintered body has a high mechanical strength and is excellent in thermal resistance. Further, a SOFC having excellent properties can be obtained by using the lanthanum gallate-based sintered body as the solid electrolyte.