Confirmation of octahedrally coordinated phosphorus in AlPO₄ -containing stishovite by ³¹P NMR

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

Source: European Journal of Mineralogy, Volume 21, Number 4, August 2009 , pp. 667-671(5)

Publisher: E. Schweizerbart'sche Verlagsbuchhandlung

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Abstract:

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. The^VI 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 only^IV P, as well as^IV Al,^VI Al, and a minor amount of^V 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.

Keywords: PHOSPHORUS; STISHOVITE; ALUMINUM PHOSPHATE; HIGH PRESSURE PHASES; NMR SPECTROSCOPY

Document Type: Research article

DOI: http://dx.doi.org/10.1127/0935-1221/2009/0021-1953

Publication date: 2009-08-01

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