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 27Al/23Na second-order quadrupolar lineshapes, are observed as a function of the I=1/2 rf field strength for both 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 19F→23Na experimental and calculated TQCP lineshapes were observed for moderate to high 19F rf field strengths.