The effect of pressure upon proton conduction in single crystals was studied by using hydrostatic pressures of up to 2GPa, at temperatures ranging from 290 to 500K. It was found that the pressure-temperature phase diagrams of these compounds, in the region of super-protonic phase transitions, exhibited a similarity that was not only qualitative but - for some parameters - was also quantitative. At pressures of up to 1GPa, the temperature of the phase transition to a state with a high proton conductivity decreased with pressure; with a slope of -47 or -59K/GPa for Rb3H(SeO4)2 and (NH4)3H(SO4)2, respectively. It was shown that new denser phases appeared at pressures of more than 1.02 or 1.22GPa in Rb3H(SeO4)2 and (NH4)3H(SO4)2, respectively. It was shown that the applied pressure caused an increase in the conductivity of super-protonic and low-conductivity phases. The activation volumes for protonic conduction in various phases of the crystals were determined. The magnitude and sign of the activation volume was correlated with the geometrical parameters of the H bond.

V.V.Sinitsyn, A.I.Baranov, E.G.Ponyatovskii: Fizika Tverdogo Tela, 1995, 37[7], 2059-69 (Physics of the Solid State, 1995, 37[7], 1121-6)