Proton magnetic resonance study of lithium ammonium sulfate

Nuclear magnetic resonance studies have been made of the protons in the ferroelectric salt NH4LiSO4. Absorption line shapes and spin–lattice relaxation times have been measured over the temperature range 77 to 400 K. The results indicate that another phase transition occurs in this material at 133 K, in addition to that previously observed at 284 K. The ammonium ions are found to be weakly hindered in the lattice, undergoing rapid general reorientations over the whole temperature range. The onset of the ionic motion is discussed in terms of simultaneous reorientations around its threefold and twofold symmetry axes.