I. R. Zachek

Features of the behavior of longitudinal static and dynamic dielectric, piezoelectric, and elastic characteristics of KH2PO4 and NH4H2PO4 crystals

Along with their electromechanical coupling coefficients, the longitudinal dielectric, piezoelectric and elastic characteristics in ferroelectric KH2PO4 and antiferroelectric NH4H2PO4 crystals are calculated using a modified proton ordering model that considers piezoelectric coupling and the four-particle cluster approximation. The possibility of detecting piezoactivity in solid solutions of K1 − x(NH4)xH2PO4 is substantiated.

Mitsui model with diagonal strains: A unified description of external pressure effect and thermal expansion of Rochelle salt NaKC_4H_4O_6·4H_2O

We elaborate a modification of the deformable two-sublattice Mitsui model of [Levitskii R.R. et al., Phys. Rev. B. 2003, 67, 174112] and [Levitskii R.R. et al., Condens. Matter Phys., 2005, 8, 881] that consistently takes into account diagonal components of the strain tensor, arising either due to external pressures or due to thermal expansion. We calculate the related to those strains thermal, piezoelectric, and elastic characteristics of the system. Using the developed fitting procedure, a set of the model parameters is found for the case of Rochelle salt crystals, providing a satisfactory agreement with the available experimental data for the hydrostatic and uniaxial pressure dependences of the Curie temperatures, temperature dependences of spontaneous diagonal strains, linear thermal expansion coefficients, elastic constants c_ij^E and c_i4^E, piezoelectric coefficients d_1i and g_1i (i=1,2,3). The hydrostatic pressure variation of dielectric permittivity is described using a derived expression for the permittivity of a partially clamped crystal. The dipole moments and the asymmetry parameter of Rochelle salt are found to increase with hydrostatic pressure.

Monoclinic elastic and piezoelectric properties of Rochelle salt. Description within the modified Mitsui model

We propose a modification of the two-sublattice Mitsui model that takes into account a coupling with diagonal components of the strain tensor. Within the developed model, we calculate the piezoelectric and elastic characteristics of Rochelle salt related to those strains. In the approximation of zero thermal expansion, we find a set of the model parameters providing a satisfactory agreement with the available experimental data for the elastic constants cEij and c E i4 and for the piezoelectric constants d1j and g1j .

Dynamics of the Rochelle salt NaKC_{4}H_{4}O_{6}·4H_{2}O crystal studied within the Mitsui model extended by piezoelectric interaction and transverse field

We calculated dynamic dielectric permittivity of the Rochelle salt within the Mitsui model, extended by piezoelectric interaction and transverse eld. Calculations were based on the parameters derived earlier within the study of thermodynamic properties of Rochelle salt. The study of dynamic properties was performed within the Bloch equation method. We showed that taking transverse eld into account allows for better description of the Rochelle salt relaxation dynamics. Furthermore, we showed that taking transverse eld into account results in the appearance of a resonant component in dynamic permittivity like it is observed in experiment. However, in accordance with the calculations, resonant response reveals itself within infrared frequency range, whereas in experiment it is observed within submillimeter spectral region.

Role of piezoelectricity in dielectric response of Rochelle salt type crystals

Comparing the spontaneous polarizations, static and dynamic dielectric properties of piezoelectric Rochelle salt and non-piezoelectric RbHSO4 we explore the role played by piezoelectric coupling in forming the dielectric response of the crystals of this type. The calculations for crystals of both types are performed within the Mitsui model, modified for the case of Rochelle salt by including the terms related to piezoelectric coupling with spontaneous strain ε4. It is shown that such a modification improves the agreement between theory and experiment for spontaneous polarization and yields a correct temperature behavior of relaxation times and dynamic dielectric permittivity of Rochelle salt in the vicinity of the transition points.

Dielectric, Electromechanical, and Elastic Properties of K1−x(NH4)xH2PO4 Compounds

We present the results of the thermodynamic theory of piezoelectric ferroelectrics and of the phenomenological theory of thermodynamic characteristics of the KH2PO4 type ferroelectrics. Available experimental data for the dielectric, piezoelectric, and elastic characteristics of the K1−x(NH4)xH2PO4 type systems are described using the proposed microscopic theory of these crystals.

Isotopic effects in partially deuterated piezoelectric crystals of Rochelle salt

We develop a theory for dielectric, piezoelectric, and elastic properties of partially deuterated (quenched disorder) crystals of Rochelle salt with taking into account the piezoelectric coupling. Results of numerical calculations are presented for a completely deuterated Rochelle salt and compared with available experimental data. Isotopic effect is explored within the mean crystal approximation, as well as within the developed theory using different trial sets of the fitting parameters. Theory predictions are given for the temperature and composition dependences of the calculated characteristics for partially deuterated crystals.

Piezocaloric and multicaloric effect in the KH2PO4 type ferroelectrics

ABSTRACT Using the proton ordering model modified by taking into account the dependence of the dipole moments on the order parameter, we explore the piezocaloric and multicaloric effects in the KH2PO4 type ferroelectrics, caused by the shear stress σ6 and longitudinal electric field E3. The multicaloric effect is shown to be stronger than either electrocaloric or piezocaloric effects, especially at temperatures far from the phase transition.

Dielectric Properties of Monoclinic RbD2PO4. The Influence of Hydrostatic Pressure

We proposed a modified proton ordering model for the quasi-one-dimensional monoclinic RbD2PO4, that takes into account linear over strains ϵi and ϵ5 contributions to the proton subsystem energy. Within the framework of the model, using the two-particle cluster approximation we calculate the static dielectric permittivity of the crystal. The dynamic dielectric permittivity of the crystal is calculated within the D.N. Zubarev nonequilibrium statistical operator method. The available experimental data for static and dynamic permittivities, are described. The effect of hydrostatic pressure on the physical characteristics of the crystal is explored.

Piezoelectric Resonance and Sound Attenuation in Rochelle Salt

A dynamic dielectric response of Rochelle salt is considered within a two-sublattice Mitsui model with piezoelectric coupling. Phenomena of crystal clamping, piezoelectric resonance, and microwave dispersion are described. Existence of a cut-off frequency for sound propagation is shown.