NMR studies of hydrogen diffusion in hydrogen uranyl phosphate tetrahydrate (HUP)

1H NMR spin-lattice relaxation times, T1 (Zeeman) and T1p (rotating frame) and spin-spin relaxation times, T2, and 31P NMR solid-echoes are reported for phase I and II of hydrogen uranyl phosphate tetrahydrate (HUP) at temperatures in the range 200-323 K. The spectral density functions extracted from the measured relaxation times for phases I and II are consistent with a 2D diffusion mechanism for hydrogen motion. 31P second moments determined from the solid-echoes show that all the hydrogens diffuse rapidly in phase I, and that the hydrogen-bond site nearest to the phosphate oxygen is not occupied in phase II. The mechanism for diffusion in phase II is discussed. 30 refs.; 6 figs.; 2 tabs