The effect of hydrostatic pressure on thermodynamic characteristics of NH3_3CH2_2COOH⋅\cdotH2_2PO3_3 type ferroelectric materials

The model of NH$_3$CH$_2$COOH$\cdot$H$_2$PO$_3$, modified by taking into account the piezoelectric coupling between the ordering structure elements and the strains $\varepsilon_i$, $\varepsilon_j$, is used for investigation of the effects that appear under external pressures. Within two-particle cluster approximation, the components of polarization vector and static dielectric permittivity tensor of the mechanically clamped and free crystals, their piezoelectric and thermal characteristics are calculated. The effect of hydrostatic pressure on the phase transition and the calculated physical characteristics of the crystal is studied. A good quantitative description of experimental data for these crystals is obtained.Comment: 14 pages, 15 figure

Deformation effects in glycinium phosphite ferroelectric

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.Comment: 17 pages, 20 figure

Electrocaloric effect in KH2_2PO4_4 family crystals

The proton ordering model for the KH$_{2}$PO$_{4}$ type ferroelectrics is modified by taking into account the dependence of the effective dipole moments on the proton ordering parameter. Within the four-particle cluster approximation we calculate the crystal polarization and explore the electrocaloric effect. Smearing of the ferroelectric phase transition by a longitudinal electric field is described. A good agreement with experiment is obtained.Comment: 10 pages, 6 figures; this article is a shortened version of arXiv:1405.1327 published in Condensed Matter Physic

Influence of electric fields on dielectric properties of GPI ferroelectric

Using modified microscopic model of GPI by taking into account the piezoelectric coupling with strains $\varepsilon_i$ in the frames of two-particle cluster approximation, the components of polarization vector and static dielectric permittivity tensor of the crystal at applying the external transverse electric fields $E_1$ and $E_3$ are calculated. An analysis of the influence of these fields on thermodynamic characteristics of GPI is carried out. A satisfactory quantitative description of the available experimental data for these characteristics has been obtained at a proper choice of the model parameters.Comment: 17 pages, 17 figure