Diffusion of ammonium ions in [(NH4)1−xRbx]3H(SO4)2 studied by 1H spin–lattice relaxation in the rotating frame

Translational diffusion of NH4+ ions in [(NH4)1−xRbx]3H(SO4)2 has been evaluated quantitatively by means of 1H spin–lattice relaxation times in the rotating frame, T1ρ. In the high-temperature phase (phase I), the mean residence times of NH4+ ions are three or four orders of magnitude larger than those of the acidic protons. In the room-temperature phase (phase II), they are two or three orders of magnitude larger than those of the acidic protons. The transition from phases II to I causes one order of magnitude enhancement in the diffusion of NH4+ ions. The mean residence time of NH4+ ions increases with increase in the Rb content. The similar trend is also observed in phase II.