Tetrahedral Tilting and Oxygen Vacancy Stabilization and Migration in LaSr(GaO)O Mixed Electronic/Oxide Ionic Conductors.

The LaO/SrO/GaO ternary system contains several compounds with remarkable oxide or proton ionic conduction. Among them, the layered LaSr(GaO)O compound is a less commonly studied material. Here, the crystal structure, electrical conduction properties, and ionic migration mechanism of the LaSr(GaO) O (0 ≤ ≤ 0.3) system are thoroughly analyzed. Diffraction methods indicate that the system crystallizes in the tetragonal space group 4/, which is compatible with the presence of a subtle GaO tetrahedral tilting along the axis, leading to a slight deviation of the body-centered tetragonal structure previously reported. This feature is essential to further understanding the mixed p electronic/oxide ion-conducting behavior of the system. Upon La for Sr substitution, oxygen vacancies arise at the loosely bound oxide sublattice, which at high temperature go through the GaO tetrahedral layer, leading to the formation of intermediate corner-sharing GaO tetrahedral dimers, and migrate via the continuous breaking and re-formation of the dimers, assisted by the synergic rotation and deformation of neighboring GaO tetrahedra. The unique structural and electrical features of LaSr(GaO)O materials within the LaO/SrO/GaO ternary system emphasize their potential application as cathode materials in LaGaO-based fuel cells.