Tetrastrontium-digalliumoxide (Sr4Ga2O7)—synthesis and crystal structure of a mixed anion strontium gallate related to perovskite

Abstract: Crystal growth experiments yielded single crystals of Sr4Ga2O7. The title compound is monoclinic, space group P1c1, , , , , , ( for 7155 observed reflections and 660 parameters). The crystals showed twinning by pseudo-merohedry. Furthermore, the diffraction data exhibited the typical features of a superstructure. Sr4Ga2O7 can be classified as a mixed anion gallate comprising insular [GaO4]-groups and [Ga3O10]-trimers. Both anion groups are located in layers perpendicular to [100]. 32 symmetrically independent Sr-cations crosslink between the tetrahedral anion groups. Alternatively, the compound can be described as a 3×4×4 superstructure of ABO3 perovskite, with 22.2% vacancies in the oxygen sublattice. The relationship with perovskite can be expressed in the following crystal chemical formula: Sr(Ga2/3Sr1/3)(O7/9□2/9)3. A discussion of the structure in the context with other similar defect perovskites in presented. [Copyright &y& Elsevier]