6Li nuclear magnetic resonance chemical shifts, coordination number and relaxation in crystalline and glassy silicates

Abstract Unlike 7 Li magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra, 6 Li MAS NMR spectra of silicates are dominated by chemical shift effects, often have a very high resolution and hence can provide significant structural information. In this study we demonstrate a good correlation between 6 Li isotropic chemical shifts and oxygen coordination number, and use this result to describe the range of coordination environments for Li in silicate glasses. We also show that the second-order quadrupolar shift for 7 Li can often be derived from 7 Li and 6 Li MAS spectra acquired at a single magnetic field. For a series of natural lepidolite samples with significant but varying contents of Mn and Fe, spin-lattice relaxation data show a power-law behavior and a three-dimensional distribution of paramagnetic centers, but homonuclear dipolar couplings can be important. The 6 Li spectrum for lithium orthosilicate (which has three-, four-, five- and six-coordinated Li) is consistent with that predicted by the X-ray structure.