Publications

The transverse dielectric constant of KD2PO4 was measured in the temperature range 79<T<322 °K. A large discontinuity appears at the transition temperature Tc indicating a well-defined first-order transition. A new feature of the data is a dome-shaped figure above Tc, resembling the magnetic susceptibility of many antiferromagnetic materials. Extension of a well-known pseudospin model for KH2PO4 to the transverse direction is achieved by taking into account the direct contribution of the displacements of the protons to the transverse polarization. Calculation of the transverse susceptibility for this model within the four-cluster approximation leads to a new independent determination of the Slater-Takagi energy configuration parameters ɛ0 and ɛ. Excellent fit to the data is achieved for the choices ɛ0kB=92 °K, ɛ1kB=907 °K and indicates that the tunneling integral for KD2PO4 is negligible. These values are very close to those derived by independent measurements of ultrasonic sould velocity and specific heat. The results of the model are also compared with the available data for the transverse susceptibility of CsH2AsO4.