Crystal structure of SrGeO(3) in the high-pressure perovskite-type phase

Single crystals of the SrGeO(3) (strontium germanium trioxide) high-pressure phase have been synthesized successfully at 6 GPa and 1223 K. The compound crystallizes with the ideal cubic perovskite-type structure (space group Pm-3m), which consists of a network of corner-linked regular GeO(6) octa­hedra (point-group symmetry m-3m), with the larger Sr atoms located at the centers of cavities in the form of SrO(12) cubocta­hedra (point-group symmetry m-3m) in the network. The degrees of covalencies included in the Sr—O and the Ge—O bonds calculated from bond valences are 20.4 and 48.9%, respectively. Thus, the Ge—O bond of the GeO(6) octa­hedron in the SrGeO(3) perovskite has a strong covalency, comparable to those of the Si—O bonds of the SiO(4) tetra­hedra in silicates with about 50% covalency. The thermal vibrations of the O atoms in the title compound are remarkably suppressed in the directions of the Ge—O bonds. This anisotropy ranks among the largest observed in stoichiometric cubic perovskites.