Tetrahedral Tilting and Oxygen Vacancy Stabilization and Migration in La 1- x Sr 2+ x (GaO 4 )O 1-0.5 x Mixed Electronic/Oxide Ionic Conductors.

The La 2 O 3 /SrO/Ga 2 O 3 ternary system contains several compounds with remarkable oxide or proton ionic conduction. Among them, the layered LaSr 2 (GaO 4 )O compound is a less commonly studied material. Here, the crystal structure, electrical conduction properties, and ionic migration mechanism of the La 1- x Sr 2+ x (GaO 4 ) O 1-0.5 x (0 ≤ x ≤ 0.3) system are thoroughly analyzed. Diffraction methods indicate that the system crystallizes in the tetragonal space group P 4/ ncc , which is compatible with the presence of a subtle GaO 4 tetrahedral tilting along the c 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 3+ for Sr 2+ substitution, oxygen vacancies arise at the loosely bound oxide sublattice, which at high temperature go through the GaO 4 tetrahedral layer, leading to the formation of intermediate corner-sharing Ga 2 O 7 tetrahedral dimers, and migrate via the continuous breaking and re-formation of the dimers, assisted by the synergic rotation and deformation of neighboring GaO 4 tetrahedra. The unique structural and electrical features of La 1- x Sr 2+ x (GaO 4 )O 1-0.5 x materials within the La 2 O 3 /SrO/Ga 2 O 3 ternary system emphasize their potential application as cathode materials in LaGaO 3 -based fuel cells.