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Influence of F content on the composition of Al-rich synthetic phlogopite: Part II. Probing the structural arrangement of aluminum in tetrahedral and octahedral layers by Al-27 MQMAS and H-1/F-19-Al-27 HETCOR and REDOR experiments

TitleInfluence of F content on the composition of Al-rich synthetic phlogopite: Part II. Probing the structural arrangement of aluminum in tetrahedral and octahedral layers by Al-27 MQMAS and H-1/F-19-Al-27 HETCOR and REDOR experiments
Publication TypeJournal Article
Year of Publication2003
AuthorsFechtelkord, M, Behrens, H, Holtz, F, Bretherton, JL, Fyfe, CA, Groat, LA, Raudsepp, M
JournalAmerican Mineralogist
Volume88
Pagination1046-1054
Date PublishedJul
Type of ArticleArticle
ISBN Number0003-004X
KeywordsANGLE-SPINNING NMR, DOUBLE-RESONANCE, F-19 MAS-NMR, FLUORINE, HIGH-FIELD, NMR, QUADRUPOLAR NUCLEI, SI-29, SOLID-STATE NMR, SPECTRA, SUBSTITUTION
Abstract

The influence of F substitution on the local structure of Al in the tetrahedral and octahedral sheets of synthetic Al-rich phlogopite samples with nominal gel compositions of K(Mg3-xAlx)[Al1+xSi3-xO10] (OH)(y)(F)(2-y) between 0.0 less than or equal to x less than or equal to 0.8 and 0.5 less than or equal to y less than or equal to 1.8, was studied by Al-27 MAS, MQMAS, {H-1/F-19} –> Al-27 2D CPMAS (HETCOR) and {H-1/F-19} Al-27 REDOR solid-state NMR and by IR spectroscopy. Changes in intensity of the absorption bands in the OH-stretching region of the IR spectra clearly indicate the incorporation of octahedral Al. Signals from the different phases can be separated in the Al-27 MQMAS NMR spectra by generation of an isotropic dimension in F1. The Al-27 quadrupolar parameters of the four phases were estimated from Al-27 MAS NMR spectra obtained at 104.26 and 208.42 MHz. The quadrupolar coupling constant and isotropic chemical shift increases with increasing Al content for the Al-IV site in phlogopite. The Al-VI site shows a clear increase of the asymmetry parameter and C-Q with increasing F content. The estimated Al-27 signal areas show the lowest amount of impurity phases at high OH contents and a stabilization of Al-VI sites by hydroxyl groups. The {H-1} –> Al-27 2D CPMAS (HETCOR) NMR experiment at short contact times provides information about site neighborhoods of tetrahedral Al sites and Mg3OH as well as Mg2AlOH sites, whereas magnetization is only transferred to the octahedral At sites from hydroxyl groups in Mg2AlOH sites. The {F-19} –> Al-27 2D CPMAS (HETCOR) NMR spectrum is dominated by Al-IV sites coupled to the Mg3F complex in phlogopite. Resonances from Mg2AlF complexes are not observed. Finally, the {H-1/F-19} Al-27 REDOR experiments support the results of the 2D CPMAS (HETCOR) experiments.

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