Pressure effect on phase transitions in MeHAO4 superprotonic conductors (A = S, Se and Me = NH4, Rb, Cs)

Abstract

The review is devoted to the behavior of some compounds of the hydrogensulfates and hydrogenselenates families under pressure. Many of these crystals undergo unusual phase transitions at ambient pressure and moderate temperatures. These transitions result in the formation of networks of dynamically disordered hydrogen bonds providing fast proton transport through the crystal structure. New additional high proton conducting (superprotonic) states can also be produced by applying pressure. Moreover, even if no superprotonic phases are formed in the compound at ambient pressure, such phases can become thermodynamically stable at high pressures, as it was demonstrated for NH4HSO4 and RbHSO4 crystals.