Experimental and theoretical investigations were made of the effect of two different types of conductivity, electrical and ionic, upon magic-angle spinning nuclear magnetic resonance spectra. The experimental demonstration of these effects involved 63Cu, 65Cu and 127I variable-temperature magic-angle spinning nuclear magnetic resonance studies of samples of γ-CuI, a Cu+-ion conductor at high temperatures as well as a wide-bandgap semiconductor. Previous observations, that the chemical shifts depended very strongly upon the square of the spinning-speed as well as the particular sample studied and the magnetic field strength, were extended. Instead, it was found that spinning bulk CuI, a p-type semiconductor due to Cu+ vacancies in non-stoichiometric samples, in a magnetic field generated induced AC electric currents that could resistively heat the sample by over 200 C. These induced currents oscillated along the rotor spinning axis at the spinning speed. Their associated heating effects were disrupted in samples containing inert filler material, indicating the existence of macroscopic current pathways between micron-sized crystallites. A theoretical analysis and finite-element simulation was presented that accounted for the magnitude and rapid time-scale of the resistive heating effects and the quadratic spinning speed dependence of the chemical shift observed experimentally. All three nuclei exhibited quadrupolar satellite transitions extending over several hundred kHz that reflected defects perturbing the cubic symmetry of the zincblende lattice. Broadening of these satellite transitions with increasing temperature arose from the onset of Cu+ ion jumps to sites having different electric field gradients. This broadening was quantitatively analyzed for the 63Cu and 65Cu nuclei by using a simple model; yielding an activation barrier of 0.64eV for the Cu+ ion jumps responsible for the ionic conductivity. This agreed with earlier results based upon the 63Cu nuclear magnetic resonance relaxation times of static samples

Electrical and Ionic Conductivity Effects on Magic-Angle Spinning Nuclear Magnetic Resonance Parameters of CuI. J.P.Yesinowski, H.D.Ladouceur, A.P.Purdy, J.B.Miller: Journal of Chemical Physics, 2010, 133[23], 234509