97-03E

On the basis of the proposed microscopic model, we study the effects of hydrostatic and uniaxial $\sigma _{3}$ pressures on the physical properties of a DADP crystal. The thermal, static and dynamic dielectric properties of a considered crystal are investigated within the cluster approximation. A thorough numerical analysis of obtained results is performed. Proper choice of the theory parameters we obtain a satisfactory description of experimental results for pressure dependence of the transition temperature of DADP. On the basis of carried calculations, we obtain possible dependences of physical characteristics on the uniaxial $\sigma _{3}$ and hydrostatic stresses. We show that it is possible to describe the pressure effects on antiferroelectric DADP and ferroelectric DKDP crystals within the same model. Further experimental study of uniaxial and hydrostatic pressure effects on the physical properties of considered crystals is required.