  To study the effects appearing under mechanical stresses, we have used the
model of glycinium phosphite ferroelectric, modified by taking into account the
piezoelectric coupling of ordering structure elements with lattice strains. In
the frames of two-particle cluster approximation, the components of
polarization vector and static dielectric permittivity tensor of the crystal,
as well as its piezoelectric and thermal characteristics are calculated.
Influence of shear stresses, hydrostatic and uniaxial pressures on the phase
transition and physical characteristics of the crystal is studied.
