V. G. Gavrilyachenko

Phase Transitions in Polarized Samples of Multicomponent Solid Solutions Based on Lead Zirconate Titanate

The physical properties of multicomponent solid solutions that are based on lead zirconate titanate and belong to the rhombohedral part of the phase diagram are investigated. The conditions for the existence of the R3c, R3m, and P4mm phases in polarized samples are determined. The region of existence of the relaxor phase is revealed.

Magnetoresistivity of La0.7Sr0.3MnO3/Sb2O3 glass composites at room temperature

The ceramic composites La0.7Sr0.3MnO3/Sb2O3 with different weight ratios of the components have been synthesized. Their magnetoresistive properties have been studied in weak magnetic fields. The values of negative isotropic magnetoresistance of the 90%La0.7Sr0.3MnO3/10% Sb2O3 composites at room temperature are found to be 1.2% and 14% for 0.25 and 20 kOe, respectively. The observed increase in magnetoresistance with an increase in the field has specific features of the relaxation process.

Phase transitions in polarized heterophase systems based on lead zirconate titanate

Temperature dependences of the depolarization currents have been studied and phase transformations between the R3c, R3m, P4mm, and Pm3m phases have been determined in samples of the five-component heterophase ferroelectric ceramics based on lead zirconate titanate.

Specific features of the dielectric spectrum of CaCu3Ti4O12 in the low-frequency range

The dielectric spectra of CaCu3Ti4O12 ceramics with giant values of the dielectric constant have been presented. The spectrum exhibits Debye dispersion with an activation energy of 0.075 eV in the high-frequency range of 106–107 Hz, and a characteristic plateau has been seen in the frequency dependence of the dielectric constant in the range of 104–105 Hz. A considerable increase in the loss factor ɛ″ has been observed in the low-frequency part of the spectrum and a capacitive-to-inductive impedance transition has been revealed in some samples at a frequency below 10−2 Hz. The causes of this transition have been discussed.

Electrical conductivity and thermopower of lead titanate crystals

The temperature dependences of the thermopower α and volume conductivity σV of lead titanate crystals have been studied in the temperature range 400–550 K, in which there are anomalies of the permittivity ɛ that are not related to the phase transition. It has been found that, in this temperature range, the thermopower α has a maximum and changes sign in many crystals; in this case, σV decreases. It has been assumed that the anomalies of α and σV, which correlate with anomalies of ɛ, are caused by thermal activation of electron traps, which leads to compensation of the p-type conductivity. The concentrations of free charge carriers and their drift mobility in the paraphase near the Curie point have been determined. These data indicate that the possibility exists of occurring the total internal screening of the bound charge Ps.

Dielectric Relaxation Phenomena in Lead Titanate Crystals

Relaxation properties of crystalline lead titanate are interpreted in terms of Maxwell-Wagner polarization.

Effect of high-temperature annealing on the dielectric properties of PbTiO3 crystals

The permittivity anomalies observed in PbTiO3 in the range 20–300°C are assumed to be initiated by electron-induced polarization of the trap—electron dipoles with relaxation. The traps are lead and oxygen vacancies. Thermal quenching of the traps suppresses the anomalies.

Dielectric spectrum of multicomponent relaxor ceramics based on PZT

ABSTRACT The dielectric spectrum of multicomponent relaxor ceramic based on PZT was studied. In non-polarized sample, Debye-type dispersion region is found with the dispersion frequency of the order of 106 Hz. During polarization of the sample, this dispersion is suppressed. It is assumed that upon cooling from the paraphrase, without applied electric field, the relaxor ceramics transition to the dipole glass state occurs. Polarization converts it into a ferroelectric state, which is confirmed by characteristic piezoresonance response in the dielectric spectrum.

Electrophysical properties of six-component ZTS-based ferrosoft ceramic

The properties of six-component ZTS-based ferrosoft ceramic are studied. The ceramic is found to exhibit properties of a ferroelectric relaxor. The R3c → R3m rhombohedral phase transition is observed in the ferroelectric phase of this composite. Polarization of samples with a constant electric field upon cooling through the Curie point enlarges the temperature range of the R3m phase’s existence, compared to roomtemperature polarization.

Dynamic fatigue during polarization switching of lead zirconate titanate ceramics with variable ferroelectric hardness

The remanent polarization of lead zirconate titanate ceramics with variable ferroelectric hardness is experimentally studied in a strong ac field. The results obtained suggest that the main mechanism of multiplication of crystal defects that controls the fatigue rate of soft ferroelectric ceramics is the process of twinning and untwinning in crystallites during polarization switching. In hard ferroelectric ceramics, the formation of a hysteresis loop is accompanied by the formation of stable configurations of mechanical twins in crystallites due to secondary twinning. Polarization switching in these configurations does not induce twin-wall motion, and the fatigue rate is low.