Phenomenological theory of phase transitions in CsHSO4

Phenomenological theory of phase transitions in superprotonic crystal CsHSO4 is developed. The explanation of phase transition between two monoclinic phases is given. The superprotonic phase of the symmetry D162h, (or D62h) is theoretically predicted. The partial proton ordering in predicted phases is constructed. The qualitative consideration of the temperature-pressure phase diagram in CsHSO4 is given.

Keywords:

• phase transition
• symmetry transformation
• order parameter
• free energy