L. A. Shuvalov

On the piezoelectric effect in acentric ferroelectric ceramics with zero polarization

Abstract Conditions sufficient for the piezoelectric effect to arise in acentric depoled (P = 0) ferroelectric ceramics whose domains possess an arbitrary polar symmetry is considered. The calculation shows that such ceramics should exhibit the piezoelectric effect if the values of the domain piezomoduli obey the conditions d 31 + d 32 + d′ 24 + d′ 15 – 2d 33 ¦ 0 and (or) d′ 14—d′ 25 ¦ 0. The measurements were made of the dependencies of the piezomodule of PZT-type ceramics on the residual polarization values. As established, the piezoelectric effect does not vanish on full electric depoling of ceramics.

The effect of mechanical stress on the properties of electrically depolarized piezoelectric ceramics

Abstract It is shown that electrically depolarized (zero remanent polarization) piezoceramics may be poled by mechanical stress. Mechanical stress applied to partially depolarized piezoceramics causes growth of polarization and change of its sign.

Phase coexistence in mixed K1-x(NH4)xH2PO4 crystals

The dielectric permittivity and polarization measurements have been performed in mixed crystals K1-x(NH4)xH2PO4 (KADP-x%) with x = 0.19, 0.24, and 0.32. It was found out that the ferroelectric phase transition in KADP-19 is preceded by a mixed ferroelectric-paraelectric state. The coexistence of ferroelectric and proton-glass states in KADP-24 takes place at low temperature.

Spatial visualization of domains in lithium niobate crystals

Abstract Visualization of 180°-domains in LiNbO3 by means of conventional polarizing microscope based on electrooptical phenomena is described. It is shown that the best results are given by visualization via pyroelectrooptical effect, when internal fields revealing the domain walls are created due to violation of the polarization and compensation of pyroeffect by screening charge. Morphological description and classification of various domain are presented. The relation between domain structure and crystal imperfections was studied. It has been proved that in LiNbO3 180°-domains are both free and pinned on macrodefects.

Domain reorientations and piezoeffect in PZT ceramics

Abstract The relationship between piezoelectric characteristics of PZT ceramics and the value of its remanent polarization has been considered in this paper. Corresponding measurements have been done. Using BaTiO3 as a model the dependencies piezomodule on the value of remnent polarization have been calculated with taking account of piezoelectric interaction between crystallites and the domain scatter in the value of a coercive field. The experimental results are explained in terms of the mentioned scatter.

Proton glass Cs5H3(SO4)4.xH2O: Relaxation dynamics

Abstract Dielectric, ultrasonic, calorimetric and dilatometric measurements were carried out in the Cs5H3(SO4)4.xH2O single crystals. Two different relaxation mechanisms in the frequency range 10−2 – 107 Hz were found. The low-frequency relaxation is of the Kohlraush form and exhibits typical glass-like behavior, while high-frequency one is described by an integral of a Debye relaxator over Gaussian distribution of relaxation times. The general nature of the acoustic and high-frequency dielectric relaxation is shown. The relation between stretched exponential and anomalous behavior of the thermal dilatation and heat capacity is discussed.

P-T-phase diagram of superprotonic conductor Rb3H(SeO4)2

The effect of hydrostatic pressure up to 2 GPa on the phase transitions has been studied in the superprotonic conductor Rb3H(SeO4)2. Among the important results of these investigations are the large decrease in the superprotonic phase transition temperature Tsi with pressure (dTsi/dP = -47 ± 7 GPa/K) and the inducing of new phase IV by the hydrostatic pressure P ≥ 1.22 GPa. The thermo-dynamical relationship between phases III, III, II, IV as well as the possibility of the existing of tetracritical point at P = 1.22 ± 0.02 GPa and T = 390 ± 2 K are discussed.

Some peculiarities of ferroelectric ordering in CsH2PO4 crystals

The influence of the bias electric field E2 on anomalies of the elastic stiffness coefficient C22 and dielectric permetivity e2 in crystals of CsH2PO4 have been studied. Strong influence of E2 on the value and shape of anomalies of C22 has been found. Below the phase transition temperature e2 e(Tc-T-γ with γ = 3 at the fields E2 e 103 V/cm.

Nonequilibrium dielectric permittivity of K1−x(NH4)xH2PO4 solid solution

Abstract The dielectric and polarization study of K1−x(NH4)xH2PO4 mixed crystals has been made. In the crystals with 0.22 ≤ × ≤ 0.72 a transition to low temperature proton glass state is realized. It was found that the dielectric dispersion of proton glass compounds is well described by the Vogel-Fulcher law. The nature of a large thermal hysteresis of polarization in the mixed crystals (x ≤ 0.22) is discussed.

Dielectric relaxation in incommensurate phase of Rb2ZnCl4 due to domain and soliton processes

Abstract 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.