The M and 1H spin-lattice relaxation rates in single crystals were measured over wide temperature ranges. The temperature dependences of the 1H spin-lattice relaxation rates in RbHSO4 and NH4HSO4 could be explained by using the Bloembergen-Purcell-Pound theory, while the temperature dependence of the 1H spin-lattice relaxation rate in KHSO4 could not. The relaxation process for M in MHSO4 crystals varied; depending upon the nature of M. It was known that the characteristic features of MHSO4 crystals depended upon whether M was K, Rb, Cs or NH4. Thus, NH4HSO4 and RbHSO4 exhibited ferro-electricity, but KHSO4 and CsHSO4 did not. Although the crystals considered were all members of the alkali acid sulfate family, the relaxation rate results varied; depending upon the mechanism of ionic motion. This suggested that the differences in the chemical properties of K, Rb, Cs and NH4 were responsible for the variations in the nature of the phase transitions in these crystals.

M and 1H NMR, Ionic Motions and Phase Transitions in Proton Conducting MHSO4 (M = K, Rb, Cs and NH4) Single Crystals. A.R.Lim, K.Y.Lim: Physica Status Solidi B, 2005, 242[12], 2417-26