Original paper

Confirmation of octahedrally coordinated phosphorus in AlPO4 -containing stishovite by31 P NMR

Stebbins, Jonathan F.; Kim, Namjun; Brunet, Fabrice; Irifune, Tetsuo


Using31 P and27 Al Nuclear Magnetic Resonance (NMR) spectroscopy, we confirm the discovery of six-coordinated phosphorus (VIP) in stishovite that contains about 1 wt% P2 O5 and Al2 O3 (synthesized at 18 GPa), as described in a recent study based on micro-X-ray Absorption Near-Edge Structure (XANES) data at the phosphorus and aluminum K -edges in a similar sample. We also confirm the presence of six-coordinated Al (VI Al) in the stishovite. TheVI P is marked by a31 P NMR peak far below the known range for phosphate groups in solid oxide materials, at 158 ppm. A sample of pure AlPO4 made under the same conditions contained onlyIV P, as well asIV Al,VI Al, and a minor amount ofV Al. Observed chemical shifts and peak shapes in this material, along with X-ray powder diffraction data (XRPD), indicate a mixture of the high-pressure form of AlPO4 (Cmcm, CrVO4 -structure), its lowcristobalite form, an amorphous phase, and one or more unknown crystalline phases.


phosphorusstishovitealuminum phosphatehigh pressure phasesnmr spectroscopy