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The process of Rb2ZnCl4 crystal repolarization under the harmonic electric field influence in the ferroelectric phase near the Curie temperature was studied by the harmonic analysis method. The stu...

The repolarization process of Rb2ZnCl4 crystals under the influence of a harmonic electric field in the ferroelectric phase in the vicinity of the domain structure freezing temperature T*≈150 K was...

The repolarization of Rb2ZnCl4 crystal under the influence of a harmonic electric field in the ferroelectric phase near the Curie temperature is studied via harmonic analysis. Study of the current density harmonics allows construction of the dependence of the density of electrical energy $${{W}_{{\text{c}}}}$$ on polarization $${{P}_{{\text{c}}}}$$ measured in the dynamics, and investigation of the temporal evolution of this dependence after destabilization of the domain structure by an alternating electric field. It is found that the nature of this dependence varies considerably during relaxation.

The reactive component $${{J}_{c}}(t)$$ and the active component $${{J}_{g}}(t)$$ time dependences by the harmonic analysis method of the current density $${{J}_{x}}(t)$$ time dependences arising in the repolarization process in the studied samples in the ferroelectric phase under the action of an electric field $$E(t)$$, whose amplitude is higher than the coercive one, are obtained. Obtained dependences analysis showed general regularities in the dynamics of the (Rb1 – xKx)2ZnCl4 crystals domain boundaries. The regularities of the defects influence on the nonlinear physical properties associated with the domain structure dynamics are revealed.

Coefficients of the expansion of electrical energy $${{W}_{c}}$$ in the ferroelectric phase near phase transition temperature $${{T}_{c}}$$ are determined from an even power series according to polarization $${{P}_{c}}$$ by studying the dynamics of repolarization in A2BX4 group crystals according to the Landau–Ginzburg–Devonshire theory. Experimental results are compared to the theoretical concepts of the Landau–Ginzburg–Devonshire theory describing dependences $${{W}_{c}}({{P}_{c}})$$ in static.

The values of the WC energy expansion coefficients in a series of PC polarization even powers on the base of study of the Rb2ZnCl4 crystal repolarization dynamics according to the theory of Landau-Devonshire are determined. The comparison of experimental results in the dynamics with theoretical concepts of the Landau-Devonshire theory describing dependencies WC(PC) in static is obtained.

Values of the expansion coefficients of electrical energy Wc in a series with respect to even powers of polarization Pc are determined using the Landau–Devonshire theory by studying the repolarization dynamics of an Rb2ZnCl4 crystal. Experimental results obtained from the dynamics are compared to theoretical representations of the Landau–Devonshire theory that describe the dependences of Wc(Pc) in statics.

Landau–Devonshire decomposition coefficients W C in a series with respect to P C are determined via harmonic analysis of experimental free energy coordinates W C of a Rb2ZnCl4 crystal, depending on its polarization P C . The number of terms needed in W C decomposition is determined for quantitative evaluation of the measured data.

Harmonic analysis of repolarization in A2BX4-group crystals in the ferroelectric phase near phase-transition temperature Tc is used to separate the contributions to the harmonic-component amplitudes in the output signal of a Sawyer-Tower circuit from charging the reference capacitor with capacitive and conductive current through such a crystal. Harmonic analysis of dielectric hysteresis loops obtained by placing a specimen in an electric field with harmonically changing strength reveals general regularities in the evolution of the domain walls of A2BX4-group crystals. It is established that the domain structure affects the nonlinear polarization properties of our specimens. The dependence of the potential relief of ferroelectric ion motion in a harmonically changing electric field is plotted on the basis of the experimental results.

Harmonic analysis of the dielectric hysteresis loops near the phase transition temperature Tc obtained under application of harmonic electric field with intensity above the intensity of the coercive field is presented. It is shown that, the direction of polarization reverses when the field value satisfies condition Ec =Em sin ϕ0. The increase in E c while approaching Tc is shown to be the reason for the anomalous temperature independent behavior of E coer.

The contributions to the amplitudes of the harmonic components of the output signal of the Soyer-Tower circuit from charging the reference capacitor with capacitive current and the conduction current of an investigated specimen are separated via the harmonic analysis of repolarization in a Rb2ZnCl4 crystal in the ferroelectric phase near the phase transition temperature Tc. Harmonic analysis of the dielectric hysteresis loops obtained when the specimen was affected by an electric field whose intensity Ein changed according to harmonic law with amplitude Em showed that at Em > Ecoer (where Ecoer is the intensity of the coercive field), the process of repolarization starts and stops when Ein reaches values of Emsin(φ0 − α0) and Emsin(φ0 + α0), respectively (where φ0 is the shift of phases between the voltage of the harmonic signal source and the voltage of the first harmonic in the reference capacitor in the Soyer-Tower circuit, and α0 is the phase corresponding to the normalized duration of repolarization). When the current value of intensity Ein coincides with Ec = Emsinφ0, the direction of polarization reverses. The increase in Ec when Tc is approached is shown to be the reason for the anomalous temperature-independent behavior of Ecoer.

Contributions from the repolarization of rubidium tetrachlorozincate Rb2ZnCl4 samples near the domain structure freezing temperature (T* ≈ 150K) and the resulting conductivity to amplitudes of the harmonic components of the Sawyer-Tower circuit output signal were separated. The nonlinear dependence of sample polarization (ignoring dielectric loss) and the dependence of instantaneous conductivity on the applied harmonic voltage were determined. It was shown that the shape of the potential profile of domain wall motion changes appreciably over a relatively narrow temperature range near T*.

The frequency dependencies of coercive field and polarization of TGS in wide frequency (10-1-104Hz) and temperature (280-330 K) ranges were observed.

The dependencies of relaxation times τ1 and τ2 at constant electric field in TGS crystals were observed.

The polarization and dielectric properties of model ferroelectric crystals of the triglycine sulphate group (TGS) and the A2BX4 group (Rb2ZnCl4) were studied. General laws of dielectric relaxation near the Curie point were determined.

Dielectric relaxation in an incommensurate phase of Rb2ZnCl4 crystal has been studied after soliton structure equilibrium was disturbed by a temperature change and an application of alternating electric field. A temperature dependence of relaxation time is discussed in terms of mechanism of phase soliton pinning by point defects.

It is shown that an equilibrium curve of temperature dependence of dielectric permittivity ex in the vicinity of the Curie point coincides with the ex (T) curve in the heating regime in commensurate phase and goes between the curves on heating and on cooling in the incommensurate phase and the equilibrium temperature of the phase transition coincides with the ex peak temperature on crystal heating.

The influence of prehistory of the Rb2ZnCl4 crystal in ferroelectric phase (FP) on the relaxation of dielectric permittivity (ϵx) in the incommensurate phase (IP) near the point of phase transition (T c) from FP into IP was studied. The analysis of the time dependences of ϵx in IP allows to speak of relaxation processes with relaxation times τ1 and τ2. It was found out that τ1 was related to the ferroelectric domain wall disappearance in IP. It is shown that the main reason of domain structure presence in IP is the pinning of domain boundaries by point defects in FP. The relaxation time τ2 is probably related to an attainment of the soliton structure equilibrium.

A comprehensive study of dielectric and polarization properties of the ferroelectric Rb2ZnCl4 crystal in the vicinity of 150 K has been performed. The investigation results were compared with the temperature dependences of threshold field of domain boundary unpinning from stoppers and relaxation time of soliton structure near this temperature. The peculiarities of dielectric and polarization properties of Rb2ZnCl4 near 150 K are discussed in terms of the ideas of the presence of structural phase transition as well as of the change in the domain wall structure that may lead to the “freezing” of the domain structure.

The noneqilibrium dielectric permittivity of the Rb2ZnCl4 crystal in the region of incommensurate phase has been investigated. It was shown that metastable states in the incommensurate phase was due to some physical processes that associated with the annihilation of domain structure at a temperature above the Curie point and the formation of incommensurate modulated wave.

The temperature evolution of the nonequilibrium dielectric permittivity of Rb2ZnCl4 crystals has been investigated in the whole metastable state region in the commensurate phase at a frequency of 1592 Hz and an electric field strength from 0.3 V/cm to 200 V/cm. A soliton and a domain contribution to the nonequilibrium dielectric permittivity has been separated.

The elastic and anelastic properties of Rb2ZnCl4 single crystals at low and infralow frequencies has been measured in temperature region including incommensurate and ferroelectric phases.

The results of investigation of low-frequency dielectric losses in the DTGSel and TGS crystals near the phase transition temperature at great amplitudes of external alternating measuring stresses are presented. The principle differences and common features of dielectric losses depending on the order of phase transition are shown.

Slow metastable states in real ferroelastics have been investigated using the inverse torsion pendulum method at infrasonic frequencies. It is shown that different physical processes leading to slow relaxation are due to the presence of domain boundaries and their interaction with defects.

The relaxation of dielectric permittivity in the classical model ferroelectric Rochelle salt within the ferroelectric phase was studied. Physical model explaining the behaviour of the relaxation time near Curie points is discussed.

Elastic and unelastic properties of K2ZnCl4 have been studied in a wide temperature range. 4Characteristic properties of the crystal at the ferroelectric phase transition at 145°K are discussed.

It is shown that at low frequencies near the ferroelectric first-order phase transition of DTGSel crystal new physical mechanisms responsible for dielectric losses take place.

The results of measurements of anelastic and elastic infra-low frequency properties of K(DxH1-x)3(SeO3)2 crystals at x=0; 0.7; 0.8; 0.85; 0.94 in the temperature range from 90 to 300 K at frequency of 10−4-10Hz are reported. The domain structure, lattice defects and crystal deuteration are shown to be responsible for the formation of mechanical hysteresis loops, the relaxation processes and shape memory effect.

Dielectric, optical and elastic properties of dimethylaminaluminiumsulphate crystals were studied. The crystal is shown to undergo a nearly tricritical second order phase transition with the symmetry change 2/m–m at Tc = 150 K. The transition can be classified as a proper ferroelectric one of the order-disorder type. Above the Tc the crystal exhibits ferroelastic behaviour.

The internal friction Q−1 in LiNbO3 single-domain and poly-domain crystals is investigated. It is found that the Q−1 maximum in the vicinity of 300°C is the supperposition of two peaks. Q−1 maxima at −30 and 300°C are discussed in terms of the interaction model between domain boundaries and two types of charged point defects having different mobilities. [Russian Text Ignored].

Temperature dependences of internal friction Q −1 and shear modulus G at the frequency of ∼ 1 c/s of KH3(SeO3)2 crystals were studied by torsion pendulum technique in the temperature range from −190°C to+50°C. Two peaks were found on the Q −1(T) curves, the first in the vicinity of Tc and the second at −150°C related to the phase transition and loss domain mechanism respectively. The measurements show that below Tc Q −1(T) and G(T) the behaviour considerably depends on domain structure state. Shear elastic stiffnesses c 44, c 55 and c 66 above Tc have been calculated from experimentally found Gx , G y and G x . It was clarified that c 55 tends to zero when T ← T c . The basic experimental results are discussed in terms of phenomenological theory.

The internal friction and elastic constants of the proper ferroelastic KH3(SeO3)2 have been studied at infralow frequencies. In the investigation the inverse torsion pendulum [1] and the apparatus for registration of mechanical hysteresis loops were used [2]. It has been found that the elastic and inelastic properties of the crystals depend substantially in the ferroelastic phase on the state and dynamics of the domain structure [3].