Proton conductivity and structural dynamics in Cs5H3(SO4)4/SiO2 composites

Cs5H3(SO4)4·yH2O and (1−x)Cs5H3(SO4)4/xSiO2 composite electrolytes (x=0.3–0.9) have been investigated by means of impedance, IR and Raman spectroscopy, differential scanning calorimetry and X-ray analysis. Cs5H3(SO4)4·yH2O has a phase transition to a high-conductive disordered state (σ∼10−2 S cm−1) at Ttr=418 K induced by changes in the structural-water content. This phase transition is shown to be reversible yet the converse transition from the high-temperature phase is slow. Although heterogeneous doping causes only a moderate increase in the low-temperature conductivity of the ionic salt, it stabilizes the high-conductive disordered state. The vibration spectroscopy data confirm the formation of the Cs5H3(SO4)4 disordered state in composites. The composite conductivity does not depend on the composition up to x=0.7 and decreases at x≥0.8 due to the percolation effect. The structural dynamics of SO4 tetrahedra is shown to correlate with the proton conductivity.