Proton dynamics in Cs2(HSO4)(H2PO4) studied by 1H NMR

Proton dynamics in Cs2(HSO4)(H2PO4) has been studied by 1H NMR. The compound shows a large thermal history. The high-temperature phase (phase HT) is retained for a considerably long period on cooling. The original room-temperature phase (phase RT) does not recover on cooling from phase HT, and another room-temperature phase (phase RT2) is produced. 1H NMR spectra indicate that reorientation of the SO4/PO4 tetrahedron takes place in phases RT and RT2 and that protons diffuse translationally in phases RT2 and HT. In all the phases, the mean residence time of protons has a distribution, being demonstrated by 1H spectral line shapes and 1H spin-lattice relaxation times. Protons diffuse with the inverse of the frequency factor (τ0) of 0.90×10−13 s and the activation energy (Ea) of 36 kJ/mol in phase HT, being obtained from analysis of the 1H spin-lattice relaxation times. These parameters can well explain the macroscopic electric conductivity. Reorientation of the SO4/PO4 tetrahedron limits the proton transport in phase HT as well as in phase RT2.