OFF-RESONANCE NUTATION NUCLEAR-MAGNETIC-RESONANCE STUDY OF FRAMEWORK ALUMINOSILICATE GLASSES WITH LI, NA, K, RB OR CS AS CHARGE-BALANCING CATION

Framework aluminosilicate glasses with varying charge-balancing cation (Li, Na, K, Rb and Cs) have been studied with Al-27 and Si-29 magic-angle spinning nuclear magnetic resonance (MAS NMR)and Al-27 on-resonance and off-resonance nutation NMR spectroscopy, This first application of off-resonance nutation NMR to disordered samples proves that it is a promising technique for the determination of mean quadrupole interactions in amorphous systems. Linewidths for Al decrease systematically with increasing size of the cation, due to a decrease in the quadrupole interaction from 5.0 MHz for the Li glass to 2.8 MHz for the Cs glass. A simple point-charge model effectively predicts the decrease in the quadrupole interaction. This indicates that the alkali ion is located close to aluminum. Looking at the residual linewidth after subtraction of the quadrupole broadening, the Al chemical shift distribution does not change significantly with the type of alkali ion. The same is true for the observed Si linewidth.