Local Structure and Protons in Non-Stoichiometric Pseudo-Cubic Pollucite Mineral by Multinuclear NMR

The pollucite structure is considered as a candidate ceramic crystalline matrix for the immobilization and long-term storage of 135Cs 137Cs fission products, thus, their structural characteristics have particular importance. However, its local has not been fully resolved from reciprocal-space techniques infrared spectroscopy, important discrepancies exist in available literature. Two birefringent non-stoichiometric specimens Tanco pegmatite (Cs0.83Na0.20Al1.13Si2.56O6) Mt. Mica (Cs0.94Na018Al1.23Si2.78O6), with powder X-ray diffraction patterns consistent cubic Ia-3d space-group symmetry, very different degree hydrothermal alteration, were used this work. High-resolution magic-angle spinning multinuclear magnetic resonance (MAS NMR) including 29Si, 27Al, 23Na, 133Cs, 1H spectra at 9.4 T, well 1H, 27Al{1H} dipolar evolutions 27Al{29Si} Heteronuclear Multiple Quantum Coherence (HMCQ) 17.6 to investigate role protons. 29Si suggest disordered Si/Al distribution only one tetrahedral T site, but preference Si atoms Q41 (3Si,1Al) Q42 (2Si,2Al) environments, comparison random Loewenstein distributions, due charge dispersion effects. two spectroscopically distinct sites Al atoms. 23Na 133Cs indicate broad site distributions these cavity cations. anisotropic character long-range structure, pseudo-cubic symmetry lack strict periodicity, can be explained an incipient displacive transition lower symmetry. These are essentially anhydrous minerals despite cross-polarization experiments suggesting that some protons -OH groups, whereas water molecules found relation phyllosilicate impurities alteration specimen perhaps also liquid fluid inclusions.