Freezing and structural relaxation in water non-stoichiometric ferroelastics of m_z h_y (ao₄)_(z+y)/2xh₂o family

Abstract

Some aspects of the ferroelastic phase transitions involving a change of a structural water con-tent in Cs₅H₃(SO₄)₄ xH₂O, Cs₅H₃(SeO₄)₄ xH₂O and K₉H₇(SO₄)₈ xH₂O single crystals are discussed. Water stoichiometric compositions (x = 1) exhibit well defined improper ferroelastic phase transitions while decreasing of water content leads to suppressing of the phase transition and supercooling of disordered paraelastic phase down to the helium temperatures. Two most interesting effects are discussed: freezing-in disordered state at low temperatures and strong influence of ambient atmosphere on the kinetics of two-phase mixed state

Key Words:

• Ferroelastics
• phase transitions
• orientational glasses
• protonic conductivity