Triple quantum cross-polarization NMR of 1H/27Al and 19F/23Na spin systems in solids

Changes in the triple quantum cross-polarization (TQCP) matching profiles and Al-27/Na-23 second-order quadrupolar lineshapes, are observed as a function of the I=1/2 rf field strength for both st;static and MAS conditions. These were interpreted by considering the orientation dependence of the nutation frequency associated with the TQ transition. Only a fraction of the spins in the powder, with specific orientations of the EFG tensor, can match the Hartmann-Hahn condition at the same time, for a fixed I=1/2 rf field strength. Good fits between F-19-->Na-23 experimental and calculated TQCP lineshapes were observed for moderate to high F-19 rf field strengths. (C) 1999 Elsevier Science B.V. All rights reserved.