• journal_title：American Mineralogist
• Contributor：Bing Zhou ; Barbara L. Sherriff ; J. Stephen Hartman ; Gang Wu
• Publisher：Mineralogical Society of America
• Date：2007-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2007.2269
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：92
• issue：1
• firstpage：34
• section：Articles

Simulations of high-resolution ¹⁹F-decoupled ²⁷Al and ²³Na magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra of the aluminofluoride minerals, cryolite, cryolithionite, thomsenolite, weberite, chiolite, prosopite, and ralstonite combined with theoretical modeling have given accurate values of chemical shift (δ_iso), and quadrupolar interaction parameters (C_q and η), thereby eliminating ambiguities incurred by the complex nuclear interactions. These NMR data have been correlated with local electronic environments in the minerals, which were calculated using Full Potential Linearized Augmented Plane Wave (FP LAPW) modeling based on the structures from X-ray diffraction (XRD) data. This combination of NMR, XRD, and modeling techniques allowed the analysis and optimization of the crystal structures.

The electronegativities and distances of neighboring ions, represented here by an environmental parameter χ, are shown to control δ_iso of both ²³Na and ²⁷Al. The calculations using χ, also show that the ions beyond the nearest neighbor play an important role in determining δ_iso of ²⁷Al and ²³Na in these aluminofluoride minerals, and the substitution of OH for F significantly affects the shielding around ²⁷Al in prosopite and ralstonite. There is a positive correlation between the site distortion at the Na and Al sites and the values of C_q in these aluminofluoride minerals.