Pressure dependence of the static and dynamic properties of KH₂PO₄ and related ferroelectric and antiferroelectric crystals

Abstract

A summary of the effects of hydrostatic pressure on the properties of KDP and related crystals is presented with some emphasis on recent results. Topics discussed include the decrease and ultimate vanishing of T_c with pressure, the underdamped soft mode, the strong deuteration dependence of the pressure effects, the pressure-induced tricritical point in KDP, the unusual pressure behavior of CsH₂PO₄ and CsD₂PO₄, the proton glass behavior of Rb,_1-x(NH₄)_xH₂PO₄ mixed crystals, and the pressure-induced crossover from classical to quantum behavior in KDP and NH₄H₂PO₄. The results emphasize that pressure studies have been very significant, if not crucial, to the discovery and/or understanding of many phenomena in these materials. It will also be pointed out that KDP at high pressure was the first known quantum ferroelectric.