The influence of hydrostatic pressure on the phase transition temperature of ferroelectric crystals of the KH2PO4-type

Abstract

The shift of the transition temperature with pressure for KH2AsO4 (dTc/dp = (−3.3 ± ± 0.2) deg/kbar) and for RbH2PO4 (dTc/dp = (−8.2 ± 0.3) deg/kbar) was determined by dielectric‐constant measurements under hydrostatic pressure up to 1.2 kbar. The experimental data are analysed using a formula for the shift of Tc with pressure derived from Kobayashi's theory.

Can the isotopic shift in KDP be explained by tunneling only?

“…The molecular-field theory gives the following expressions for the susceptibility in the paraelectric phase x , for the transition temperature Tc, and for the spon- The tunneling is of no importance at very high temperatures where it can be written 1) In (2) also the molecular-field approximation was used. Table 1 Estimates of important quantities for the three isomorphous substances D H The data in brackets are calculated under the assumption a), i. e. J = J *) Data from paper (2).…”

“…cent measurements (2) of the pressure dependence of the transition point indicate that the ltferroelectric" interaction between the protons is appreciably weaker than between the deuterons. It opens the possibility to attribute a large part of the isotopic shift to changes in "ferroelectric" interaction.…”

Influence of Tunneling on Dielectric Behaviour of KH2PO4

“…A series of measurements (far infrared absorption (3), Raman scattering (4), and T shift with hydrostatic pressure (5)) has been carried out to demonstrate the role of the tunneling mechanism. The evaluation of S2 from the measurements mentioned requires further information on the KDP dynamics, e.g., data on the protonlattice interaction o r the knowledge of the form of the potential along the hydrogen bond.…”