Sr-fresnoite determined from synchrotron X-ray powder diffraction data

The fresnoite-type compound Sr₂TiO(Si₂O₇), distrontium oxidotitanium disilicate, has been prepared by high-temperature solid-state synthesis. The results of a Rietveld refinement study, based on high-resolution synchrotron X-ray powder diffraction data, show that the title compound crystallizes in the space group P4bm and adopts the structure of other fresnoite-type mineral samples with general formula A₂TiO(Si₂O₇) (A = alkaline earth metal cation). The structure consists of titanosilicate layers composed of corner-sharing SiO₄ tetra­hedra (forming Si₂O₇ disilicate units) and TiO₅ square-based pyramids. These layers extend parallel to the ab plane and are stacked along the c axis. Layers of distorted SrO₆ octa­hedra lie between the titanosilicate layers. The Sr²⁺ ion, the SiO₄ tetra­hedron and the bridging O atom of the disilicate unit are located on mirror planes whereas the TiO₅ square-based pyramid is located on a fourfold rotation axis.