A. V. Shil’nikov

Dielectric and electromechanical properties of (1−x)PMN-xPZT ferroelectric ceramics

The dielectric and electromechanical characteristics of the (1−x)PMN-xPZT ferroelectric ceramics have been obtained at different temperatures, amplitudes, and frequencies of the measuring field and at different bias field strengths. It is shown that this ferroelectric ceramics at low and infralow frequencies possesses pronounced relaxor properties in a certain temperature range and ferroelectric properties in other temperature range. The temperature and amplitude ranges have been determined, in which the permittivity ɛ′ either only decreases or first increases and then decreases with an increase in the measuring field amplitude E0. The temperature ranges of existing the phases similar to the superparaelectric phase, dipole glass phase, and ferroelectric phase are evaluated from the temperature dependences of the coercive field Ec(T) and the remanent polarization Pr(T) and also from the reverse dependences of ɛ* and the electromechanical characteristics. The PZT concentration in the PMN-PZT system is determined, at which the electrostrictive constant M11 is maximum. It is demonstrated that, in the neighborhood of the temperature at a maximum of ɛ′, the strain S3 is quadratic in the field E=; that is, S3=M11E2.

Specific features of the electrical properties upon smeared phase transitions in multicomponent ferropiezoelectric ceramics based on lead zirconate titanate

The reverse dependences of the permittivity ɛr′ (E=) and the polarization and depolarization currents in multicomponent ferropiezoelectric ceramics based on lead zirconate titanate (PZT) are investigated over a wide range of temperatures. The results obtained make it possible to separate the effects associated with the phase transformation and the effects predominantly caused by the switching of the domain structure in the studied material. The assumption is made that two smeared phase transitions occur in the system under consideration.

Effect of gamma irradiation on the dielectric response of a Sr0.75Ba0.25Nb2O6 relaxor single crystal

The effect of gamma irradiation from a 60Co source at a dose D = 4.75 × 104 R on the dielectric properties of a Sr0.75Ba0.25Nb2O6 (SBN-75) single crystal with a smeared phase transition is investigated in the low-and infralow-frequency ranges. The behavior of the dielectric response is compared with the behavior of the depolarization currents induced in unirradiated and irradiated samples of the Sr0.75Ba0.25Nb2O6 compound. The observed changes in the electrical properties of the Sr0.75Ba0.25Nb2O6 single crystal in the temperature range of the smeared phase transition are associated with the stabilization of the ferroelectric phase of the material in an internal bias field generated by radiation-induced defects.

Dielectric properties of single-crystal deuterated triglycine sulfate (DTGS) in ultra-weak low-and infra-low-frequency electric fields

The complex permittivity ɛ* is studied with separate readings for ɛ′ and ɛ″ at low and infralow frequencies and ultraweak fields. The effective conductivity λ is determined. An Arrhenius dependence is observed for ln ɛ′(1/T), ln ɛ″(1/T), and ln λ(1/T), both in the paraphase and in the polar phase. It is proposed that the conductivity of crystalline DTGS in the paraphase is an ion jump conductivity.

Effect of mechanical stresses on the dielectric response of PZT ferroelectric thin films

This paper reports on the results of the investigation into the effect of mechanical stresses on the dielectric properties of PZT ferroelectric thin films. An external load G applied to the sample brings about an increase in the residual tensile stress along one of the axes of the film. It is demonstrated that, in weak and moderate electric fields, an increase in the stress σ leads to an increase in the permittivity ε′ of the sample. A further increase in the strength of the measuring electric field results in the opposite effect: the permittivity ε′ decreases with increasing external load G. The observed effects are explained in terms of the specific features revealed in the behavior of the domain structure of the ferroelectric thin films in fields of internal stresses.

The contributions from different mechanisms of motion of domain boundaries to the effective permittivity of triglycine sulfate crystals in moderate low-and infralow-frequency fields

A study of the special features of contribution of domain boundaries to the effective permittivity ɛeff* of a TGS crystal is made in electric fields of various frequencies and in a wide temperature range of the polar phase, up to the phase transition temperature. In considering the experimental data obtained, we classify the defects into three types depending on their interaction strength with the domain boundaries. Using the approach developed, we explain the frequency and temperature dependences of the contributions from the hysteretic and relaxation mechanisms of motion of the domain boundaries to ɛeff*

Investigation of the low-and infralow-frequency dielectric response of Ba0.7Sr0.3TiO3 thin films

The low-and infralow-frequency dielectric properties of Ba0.7Sr0.3TiO3 thin films annealed at temperatures of 750 and 900°C are investigated over wide ranges of temperatures (from −180 to +100°C), frequencies (from 0.1 Hz to 10.0 kHz), and amplitudes of the measuring electric field (from 15 to 255 kV/cm). The samples are found to undergo giant relaxation characteristic of layered heterogeneous structures. It is noted that, at a higher annealing temperature (900°C), the relaxation region is shifted toward lower temperatures (higher frequencies).

Reverse dependences of the permittivity of xPZN − (1 − x)PSN ferroelectric ceramics on the bias electric field

The effect of bias electric fields E= on the dielectric response of xPZN − (1 − x)PSN ferroelectric solid solutions with PZN contents x = 0, 0.05, 0.20, and 0.50 is investigated in the temperature ranges corresponding to the smeared phase transitions of the studied compounds. It is concluded that an increase in the PZN content in this system leads to a narrowing of the temperature range of existence of the relaxor phase.

Effect of an Electric Field on the Fracture of Ferroelectric Ceramic Materials

This paper reports on the experimental results of measuring the time elapsed between the loading and the fracture of ferroelectric ceramic specimens under the action of a static electric field and mechanical stresses that differ in magnitude. The dependence of the durability of the specimens on the applied stress is determined for electric fields in the range from 0 to 5 MV/m. It is shown that, in the time range 1–103 s, the durability of the ferroelectric ceramic material substantially increases in weak electric fields (the hardening effect) and significantly decreases in strong electric fields. The results obtained can be explained in terms of the fact that the load and the electric field affect the same defects (fracture nuclei) in the ferroelectric ceramics.

Long-time relaxation phenomena in Pb0.94Ba0.06Sc0.5Nb0.5O3 (PBSN-6) single crystals

Long-time polarization relaxation in the temperature range where PBSN-6 single crystals reside in the relaxor state was studied. An analysis of the time dependence of the permittivity ε′(t) performed at measuring frequencies from 1 Hz to 1 kHz in weak electric fields E0 showed that the relaxation (or freezing) times derived by extrapolating relations of the type ε′(t) ∼ log(t/t0) and ε′(t) ∼ exp{−[ln(t/t0)]β} range from 108 to 1011 min and depend substantially on the bias voltage applied to the sample. A study of the pattern of the dielectric response in moderate and strong infralow-frequency fields revealed that, after a sample was maintained under a bias lower than the coercive force, it no longer exhibited the additional anomalies in the amplitude dependences of the effective loss tangent taneff(E0) than were observed in a thermally recuperated sample.