Structure of a new form of silicon phosphate (SiP{sub 2}O{sub 7}) synthesized at high pressures and temperatures

• Published in: Journal of solid state chemistry Vol. 190
• Main Authors: Leinenweber, Kurt, Stearns, Linda A., Nite, Jacob M., Nemeth, Peter, Groy, Thomas L.
• Format: Journal Article
• Language: English
• Published: United States 15-06-2012
• Subjects: CARBIDES; CESIUM CHLORIDES; DIMERS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; LATTICE PARAMETERS; MONOCLINIC LATTICES; MONOCRYSTALS; PYROPHOSPHATES; SILICON PHOSPHATES; SPACE GROUPS; SYMMETRY; TOPOLOGY
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/J.JSSC.2012.02.031

A new high-pressure phase of SiP{sub 2}O{sub 7} has been found and its crystal structure solved and refined from a single crystal grown at a condition of 16 GPa and 2000 Degree-Sign C and recovered to ambient conditions. The material is monoclinic, with the space group P2{sub 1}/c and lattice parameters a=4.3042(7) A, b=7.1505(12) A, c=6.2897(11) A, {beta}=103.805(2). The structure contains SiO{sub 6} octahedra in a corner-sharing arrangement with P{sub 2}O{sub 7} dimers, the same structural elements and vertex-sharing present in all the low-pressure forms of SiP{sub 2}O{sub 7}. However, the network is more condensed: the topology of the packing of SiO{sub 6} octahedra and P{sub 2}O{sub 7} dimers (represented by Si and the bridging oxygen that both lie on centers of symmetry) is that of the CsCl structure, with some distortion. The resulting phase is 11.2% to 22.3% denser than the various low-pressure forms of SiP{sub 2}O{sub 7}. The structural data indicates that the P{sub 2}O{sub 7} dimers are linear (P-O-P angle=180 Degree-Sign ), an unusual feature for phosphates. - Graphical abstract: Single crystals of a new form of SiP{sub 2}O{sub 7} were synthesized at high pressure and temperature and the structure solved. Left: the high pressure multi-anvil assembly in a nest of 25.4 mm carbide anvil cubes. Center: the high pressure multi-anvil apparatus. Right: the monoclinic structure of the new phase: blue octahedra are SiO{sub 6} units and the yellow tetrahedra are PO{sub 4} units. Highlights: Black-Right-Pointing-Pointer Silicon phosphate transforms into a new phase at high pressure and temperature. Black-Right-Pointing-Pointer The high pressure phase is 14.8% denser than the low-pressure phase. Black-Right-Pointing-Pointer The structure is based on a linkage of SiO{sub 6} polyhedra and P{sub 2}O{sub 7} dimers. Black-Right-Pointing-Pointer The way the two units are packed is reminiscent of the CsCl arrangement. Black-Right-Pointing-Pointer The new structure is monoclinic and is a unique structure.