Proton dynamics in [(NH4)1−xRbx]3H(SO4)2 with x = 0.54 were studied by means of 1H solid-state nuclear magnetic resonance. The 1H magic-angle-spinning nuclear magnetic resonance spectra were traced at room temperature, and 1H static nuclear magnetic resonance spectra and spin-lattice relaxation times (T1) were measured at 296 to 490K. The 1H chemical shift for the acidic proton (15.4ppm) indicated H bonds of intermediate strength between (NH4)3H(SO4)2 and Rb3H(SO4)2. In phase II, a very fast local and anisotropic motion of the acidic protons takes place and NH4+ ions start to diffuse translationally just below the transition temperature. In phase I, both NH4+ ions and the acidic protons diffuse translationally. The acidic protons diffuse with an activation energy of 29kJ/mol and the inverse of a frequency factor of 6.0 x 10−13s. No proton exchange was observed between NH4+ ions and the acidic protons in both phases.

1H NMR Study of Proton Dynamics in [(NH4)1−xRbx]3H(SO4)2 (x = 0.54). H.Omi, K.Suzuki, S.Hayashi: Solid State Ionics, 2008, 179[21-26], 842-6