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

摘要

A new high-pressure phase, silicon phosphate hydroxide, was prepared at 8.3 +/- 0.5 GPa and 1000 degrees C in > 98% 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 P2(1) (No. 14), a = 6.8446(11) angstrom, b = 6.8683(13) angstrom, c = 6.8446(11) angstrom, beta = 11 9.77(1)degrees, and Z = 4. The refinement gave a conventional R-obs of 0.0320 and wR(obs), 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 HgSeO(4)center dot H2O. It is also related to the SbOPO4 structure by a small distortion that lowers the symmetry from C2/c in SbOPO4 to P2(1)/c (P2(1)) in SiPO4(OH). (c) 2005 Elsevier Inc. All rights reserved.