The effect of pressure upon phase transitions and protonic conductivity was studied at pressures of up to 2GPa, and at temperatures of between 300 and 500K (table 12). It was found that the temperature of the super-protonic transition in both crystals decreased with pressure at pressures of up to 1GPa. New phases originated in Rb3H(SeO4)2 at pressures above 1.22GPa, and in (NH4)3H(SO4)2 at pressures above 1.02GPa. The activation volumes of low- and high-conductivity phases were deduced from the pressure dependences of the protonic conductivity.

V.V.Sinitsyn, A.I.Baranov, E.G.Ponyatovsky, L.A.Shuvalov: Solid State Ionics, 1995, 77, 118-21

Table 12

Conductivity Parameters (c-axis) for (NH4)3H(SO4)2 and Rb3H(SeO4)2