MEIONITE: RIETVELD STRUCTURE-REFINEMENT, 29Si MAS AND 27Al SATRAS NMR SPECTROSCOPY, AND COMMENTS ON THE MARIALITE MEIONITE SERIES

Abstract

Rietveld structure refinement, 29 Si magic angle spinning (MAS) and 27 Al satellite transition (SATRAS) NMR spectroscopic data are given for three natural samples of meionite and for synthetic end-member meionite. Trends in structural parameters and NMR spectra are discussed for the solid-solution series from marialite to meionite. The a cell dimension and 27 Al SATRAS NMR spectra show a continuous change through the series, whereas the space group, c cell dimension and 29 Si MAS NMR spectra show different trends for the three subseries, Si 9.0–8.3, Si8.3–7.4 and Si7.4–6.0. Over the interval Si 9.0–8.3, the space group is I4/m, the c cell dimension increases with Al content, and 29 Si spectra show multiple well-resolved peaks; the anion site is occupied by Cl – , and the T(1) site, by Si. Si–Al order between the T(2) and T(3) sites causes the space group for Si 8.3–7.4 to be P42/n and the 29 Si MAS NMR spectra to be dominated by Si(1) (3Si1Al) and Si(3) (1Si3Al) peaks. Here, there is a negative correlation between c cell dimension and Al content. Over the interval Si 7.4–6.0, the c cell parameter increases with Al content, the space group is I4/m, and multiple 29 Si MAS NMR peaks become broad and poorly resolved. Ca 2+ continues to replace monovalent cations in the M site,