A study of the phase transitions and structural chemistry of CsH3(SO4)2 and Cs3H(SO4)2 single crystals using H1 and C133s nuclear magnetic resonances

Abstract

The H1 and C133s spin-lattice and spin-spin relaxation times of CsH3(SO4)2 and Cs3H(SO4)2 single crystals were measured using nuclear magnetic resonance (NMR) near the phase transition temperatures of these crystals. CsH3(SO4)2 crystals undergo three phase transitions at high temperatures (TC1=320 K, TC2=420 K, and TC3=496 K), whereas Cs3H(SO4)2 undergoes four phase transitions (TC1=225 K, TC2=253 K, TC3=306 K, and TC4=419 K). The behavior of T1 for the H1 and C133s nuclei in the two crystals differs markedly. For CsH3(SO4)2, the H1 spin-lattice relaxation time increases with increasing temperature, whereas for Cs3H(SO4)2 this relaxation time decreases with increasing temperature. These results indicate that the molecular motion of H1 in the proton-rich CsH3(SO4)2 crystals differs from that of H1 in Cs3H(SO4)2 crystals. The changes in the H1 and C133s spin-lattice relaxation times at the phase transition temperatures result from changes in the environments of the H1 and C133s nuclei during the transitions. In addition, the spin-lattice relaxation times of the CsH3(SO4)2 and Cs3H(SO4)2 crystals indicate that they have superionic character above TC2 (=420 K) and TC1 (=225 K), respectively. Further, new hydrogen sulfates of alkaline metals are discussed in terms of their hydrogen-bonding systems. For compounds of formula CsXHNSO4 (where M is an alkali metal, X+N=2), the value of N gives the average number of hydrogen donor functions (OH groups) per SO4 tetrahedron. The N value defines the main features of the hydrogen-bonding systems.