High-pressure synthesis and crystal structure of silicon phosphate hydroxide, SiPO4(OH)

A new high-pressure phase, silicon phosphate hydroxide, was prepared at image and 1000 °C in image purity. From X-ray diffraction on a pseudo-merohedrally twinned crystal, it was found that SiPO4(OH) crystallizes in a monoclinic cell with space group image (No. 14), image, and image. The refinement gave a conventional image of 0.0320 and image of 0.0864 for the overlapped data from both twin components. In the structure, SiO6 octahedra form chains along [101], with PO4 tetrahedra alternating along the chain in the b-direction. The parallel chains link up with tetrahedral corners from other chains to form a 3-dimensional network. SiPO4(OH) belongs to a structural family that includes image. It is also related to the SbOPO4 structure by a small distortion that lowers the symmetry from image in SbOPO4 to image in SiPO4(OH).