NMR investigation of ammonium ion motions in two ammonium bisulfates

Nuclear magnetic second moment and spin–lattice relaxation time studies have been performed over the temperature range 77–388 K for two ammonium bisulfates; the ferroelectric NH4HSO4 and the antiferroelectric (NH4)3H(SO4)2. The results suggest a rapid general reorientation of the NH4 + ions over the whole temperature range in both materials, brought about by the superposition of a threefold reorientation on two less hindered twofold reorientations. The NH4HSO4 shows an additional mechanism, absent from the (NH4)3H(SO4)2 results, which is attributed to a loss of distortion of the NH4 + tetrahedron at high reorientational frequencies.