Single- and Double-Resonance Experiments of Quadrupolar Nuclei in Solids Using Sensitivity Enhancement of the Central Transition

Population enhancement for NMR of the central transition of quadrupolar nuclei in solids is performed by using adiabatic radiofrequency sweeps of the satellite transitions. Single-resonance experiments are reported for ¹⁷O, ²³Na, ²⁷Al, and ⁹³Nb nuclei in powders of Al₂O₃, NaNbO₃, and LiNbO₃, and in Pyrex glass. Experimental techniques using single-coil probe circuits capable of both wideband frequency sweeps and narrowband detection are presented. The combination of population enhancement with cross polarization from ²⁷Al to ¹⁷O in α-Al₂O₃ (corundum) powder is demonstrated. The sensitivity-enhancement technique is robust, with no critical parameters.