Title: THERMODYNAMICS AND DIELECTRIC PROPERTIES OF KH_2PO_4, RbH_2PO_4, KH_2AsO_4, RbH_2AsO_4 FERROELECTRICS
Author(s): R.R.Levitskii, B.M.Lisnii, O.R.Baran (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine)

Within the proton ordering model with taking into account the short-range and long-range interactions as well as tunnelling effects, in the framework of the cluster approximation, we study the thermodynamic and static dielectric properties of the \kdp type ferroelectrics. Theoretical results are compared with the corresponding experimental data and with the results of theoretical calculations of other sources. We show that under the proper choice of the theory parameters, a very good quantitative description of the available experimental data is obtained for the temperature dependence of spontaneous polarization, specific heat, longitudinal and transverse static dielectric permittivities, as well for the Curie-Weiss temperature and constant.
Suitability of the model for the description of experimental data for the crystals \kdp, \rdp, \kda, \rda without taking into account striction, fluctuations, and other effects is discussed.

Key words: cluster approximation, KDP, tunnelling, phase transition, dielectric permittivity, Curie-Weiss temperature, Curie-Weiss constant
PACS: 77.22.Ch, 77.80.Bh, 77.84.Fa