In the present work, our aim is to decipher the cationic ordering in the octahedral and tetrahedral sheets of two Al-rich synthetic materials, namely, phlogopites of nominal composition K(Mg3-x Alx )[Al1+x Si3-x O10 ](OH)y F2-y and lepidolites in the system trilithionite-polylithionite with composition K (Lix Al3-x )[Al4-2x Si2x O10 ](OH)y F2-y , by directly probing the aluminium distribution through 27 Al and 17 O magic-angle spinning, multiple-quantum magic-angle spinning, and 27 Al-27 Al double-quantum single-quantum nuclear magnetic resonance (NMR) experiments. Notably, 27 Al-27 Al double-quantum single-quantum magic-angle spinning NMR spectra, recorded at 9.34 and/or 20.00 T, show the spatial proximity or avoidance of the Al species inside or between the sheets. In both studied minerals, the ensemble of NMR data suggests a preference for [4] Al in the tetrahedral sheet to occupy position close to the [6] Al of the octahedral sheets.
Keywords: 17O MAS NMR; 27Al MAS NMR; cation ordering; lepidolite; phlogopite.
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