Structure of a new form of silicon phosphate (SiP2O7) synthesized at high pressures and temperatures

► Silicon phosphate transforms into a new phase at high pressure and temperature. ► The high pressure phase is 14.8% denser than the low-pressure phase. ► The structure is based on a linkage of SiO6 polyhedra and P2O7 dimers. ► The way the two units are packed is reminiscent of the CsCl arrangement. ► The new structure is monoclinic and is a unique structure.