Abstract
The phase transitions and proton dynamics of Cs 5H 3(SO 4) 4·0.5H 2O single crystals were studied by measuring the NMR line shape, the spin-lattice relaxation time, T 1, and the spin–spin relaxation time, T 2, of the 1H and 133Cs nuclei. The “acid” protons and the “water” protons in Cs 5H 3(SO 4) 4·0.5H 2O were distinguished. The loss of water protons was observed above T C1, whereas the content of water protons was found to recover above T C2. Therefore, the water protons play a special role in the stability of the superprotonic phase at high temperatures. The mechanism of fast proton conduction was found to consist of hydrogen-bond proton transfer involving the breakage of the weak part of the hydrogen bond and the formation of a new hydrogen bond. Thus, these structural phase transitions probably involve significant reorientation of the SO 4 tetrahedra and dynamical disorder of the hydrogen bonds between them.
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