08-04U

Within the proposed unified proton model for ferroelectric KH$_2$PO$_4$ type compounds thermodynamic and longitudinal and transverse dynamic characteristics of the KH$_2$PO$_4$ type ferroelectrics and the NH$_4$H$_2$PO$_4$ type antiferroelectrics are calculated in the four-particle cluster approximation taking into account short-range and long-range interactions. Theoretical calculation results for K(H$_{1-x}$D$_{x}$)$_2$PO$_4$ type ferroelectrics and N(H$_{1-x}$D$_{x}$)$_4$(H$_{1-x}$D$_{x}$)$_2$PO$_4$ type antiferroelectrics obtained in mean crystall approximation are compared with corresponding experimental data is done. At proper choice of a parameter set the developed theory provides correct description of the experimental data for these compounds.