Pressure effect on superprotonic phase transition in mixed [(NH4)xRb1−x]3H(SO4)2 crystals

The pressure effect on the superprotonic phase transition temperatures is studied for the series of [(NH4)xRb1−x]3H(SO4)2 mixed crystals, x=0, 0.2, 0.5, 0.8 and 1. It is shown that the R3m superprotonic phase does not occur in Rb3H(SO4)2 at atmospheric pressure, but becomes stable at a pressure greater than 0.14 GPa. The scaling correlation is found between the A2/a–R3m transition lines in all P–T phase diagrams studied.