Proton dynamics in Cs3(HSO4)2(HPO4) studied by 1H NMR

Proton dynamics in Cs3(HSO4)2(H2PO4) has been studied by means of 1H solid-state NMR as well as thermal analyses. The thermal analysis shows an endothermic peak at 408 K, which corresponds to a superprotonic transition. Above the transition temperature a mass loss is observed in a dry atmosphere, which is easily recovered in a conventional dry atmosphere below the transition temperature. The 1H magic-angle-spinning NMR spectra at room temperature show two peaks at 13.5 and 15.8 ppm, and a shoulder at 11.3 ppm from tetramethylsilane, demonstrating a presence of several inequivalent proton sites. Translational diffusion of protons takes place in both a room-temperature phase (RT) and a high-temperature phase (HT). In both phases reorientation of the SO4/PO4 tetrahedron limits the rate of the proton transport. The 1H mean residence times are estimated as Ea = 33 kJ mol− 1 and τ0 = 0.97 × 10− 9 s for phase RT from the second moment analysis and as Ea = 20 kJ mol− 1 and τ0 = 5.0 × 10− 12 s for phase HT from the analysis of the 1H T1 results.