Lead Magnoniobate Research Articles

The delay time of phase transition to the polar phase in relaxor ferroelectrics

We measured the time dependence behavior of the dielectric permittivity of lead lanthanum zirconate titanate (PLZT) transparent ceramic sample and a single-crystal lead magnoniobate (PMN) from the moment of the field application at certain temperatures after the zero-field cooled regime. The delay time of the phase transition from the glasslike state to the field-induced ferroelectric state was determined from the sharp change in the dielectric permittivity in PMN single crystal. The same transition in PLZT has more smooth behavior. We found the temperature dependence of the delay time of the phase transition under ultraviolet illumination for PMN single crystal.

Influence of composition nonstoichiometry and ordering effects on the properties of ferroelectric ceramics based on lead magnoniobate

The effects of violation of the stoichiometry of lead magnoniobate in the preparation of compositions (1-x)PbMg1/3Nb2/3O3 – xPbMg1/2Nb1/2O2,75 with a step of 0.1 and 0≤x≤1 have been studied by X-ray diffraction methods. Differences in the unit cell parameters of the ferroelectric ceramic samples of the composition under study were found. It was shown that the effect of ordering of different types of atoms in the cells, leading to the formation of a superstructure and a doubling of the lattice period, was not observed in any of the samples. . Measurements of the dielectric constant of the synthesized samples and the tangent of the dielectric loss angle showed a violation of the Curie-Weiss law, which indicates the diffusion of the phase transition.

Combined Real-Time Study of Dielectric Response and Piezoresponse of Pb(Mg1/3Nb2/3)O3 Relaxor in an Electric Field

A method of synchronous measurement of the piezoresponse signal and electrical impedance when studying the processes of polarization switching in an external electric field has been described. Using the developed technique, the processes of switching ferroelectric (FE) phase of lead magnoniobate induced by an electric field are studied. It is shown that a polydomain structure with a weak piezoresponse is formed during the initial appearance of the FE phase. A change in the direction of the external field leads to polarization switching, and the switching process passes through an intermediate glass-like phase. Training the sample by multiple switching leads to a sharp increase in piezoresponse, which can be associated with a single-domain state formation.

The delay of phase transition to the polar phase in relaxors: influence of ultraviolet illumination

The time dependence behavior of the dielectric permittivity of lead lanthanum zirconate titanate transparent ceramic sample from the moment of the field application at certain temperatures after the zero-field cooled regime is compared to that exhibited by a single-crystal lead magnoniobate. The delay time of the phase transition from the glasslike to the field-induced ferroelectric state was determined from the sharp change in the dielectric permittivity in a lead magnoniobate single crystal. The same transition in lead lanthanum zirconate titanate has more smooth behavior. In the case of ultraviolet illumination, the delay becomes a few times shorter for both cases.

Совместное исследование диэлектрического и пьезотклика релаксора Pb(Mg-=SUB=-1/3-=/SUB=-Nb-=SUB=-2/3-=/SUB=-)O-=SUB=-3-=/SUB=- в реальном масштабе времени при приложении электрического поля

The method of the study of the polarization switching processes in ferroelectrics by an external electric field using synchronous measurement of an electric impedance and piezoelectric response is described. Using the developed technique, the switching processes in the electric field-induced ferroelectric phase (FE) of lead magnoniobate are studied. It is shown that, upon the initial occurrence of the SE phase, a multidomain structure with a weak piezoelectric response is formed. A change in the direction of the external field leads to polarization switching, and the switching process passes through an intermediate glassy phase. raining a sample by repeated switching leads to a sharp increase in the piezoelectric response, which can be attributed to the formation of a single-domain state.

Temperature Dependences of Structural Parameters of PMN in the Region of Diffuse Phase Transition

In this work, we analyzed the structural parameters of the lead magnoniobate sample in the temperature range from 20 ºC to 450 ºC by X- ray structural analysis. It was found that the PMN cubic perovskite cell does not undergo distortions over the entire temperature range under study. In the vicinity of a temperature of 250 ºC in PMN, an abrupt decrease in the coefficient of linear expansion from 1.06∙10-5 K-1 to 0.32∙10-5 K-1, which is possibly associated with a change in the anharmonicity of the potential relief of atoms in the structure, is recorded.

Optical stimulated transfer from glass state to polar phase in relaxors

We measured the time dependences of the dielectric permittivity of a single crystal lead magnoniobate in [110] orientation from the moment of the field application at the certain temperatures after the zero-field cooled regime. The delay time of the phase transition from the glasslike to the field-induced ferroelectric state was determined for the sharp change in the dielectric permittivity at the several temperatures. The phase transition to the ferroelectric state was confirmed by measuring the pyroelectric current. Then the same experiment was repeated in illumination condition. The effect of illumination on the delay time of the phase transition was investigated. In the case of ultraviolet illumination, the delay time became few times shorter.

Electrocaloric Effect in a Lead Magnoniobate–Scandoniobate Relaxor

The electrocaloric effect and also the dielectric, pyroelectric, acoustic, and piezoelectric properties of a lead magnoniobate–scandoniobate solid solution in a biasing electric field have been studied. The dielectric and electromechanical contributions to the pyroelectric and electrocaloric effects are discussed.

Photostimulated Currents in Single Crystals of Lead Magnoniobate and Lead Magnoniobate Titanate

The spectral dependences of photostimulated currents in single crystals of lead magnoniobate and lead magnoniobate titanate are investigated. The results suggest that the distribution of the density of impurity states in the bandgap of the studied crystals is quite wide. These levels could participate in the formation of diffuse phase transitions.

Электрокалорический эффект в релаксоре магнониобате-скандонибате свинца

AbstractThe electrocaloric effect and also the dielectric, pyroelectric, acoustic, and piezoelectric properties of a lead magnoniobate–scandoniobate solid solution in a biasing electric field have been studied. The dielectric and electromechanical contributions to the pyroelectric and electrocaloric effects are discussed.

Analysis on the anisotropic electromechanical properties of lead magnoniobate titanate single crystal for ring type ultrasonic motors

This work discussed the optimized cut of single crystal lead magnoniobate titanate (PMNT) for use of ring type travelling wave ultrasonic motors (USMs), according to anisotropic analysis on electromechanical properties. The selection criterion of crystal orientation relies on the circular uniformity of the induced travelling wave amplitude on the stator surface. By calculating the equivalent elastic coefficient c11 and lateral piezoelectric constant d31, the optimal crystal orientations were proposed for PMNT single crystals poled along different directions. For single crystal poled along <001>c directions, the optimal orientation lies along [001]c with d31=-1335pC/N and k31=0.87. The crystallographic orientation [025]c is the optimized orientation for single crystals poled along <011>c direction with d31=199pC/N and k31=0.55. The optimal orientation of 1R configuration is [332¯]c with a large enhancement of d31 = 1201 and k31=0.92.

Low-frequency polarization relaxation in PMN + 2% Li2O ferroelectric ceramics in the region of diffuse phase transition

Studies of dielectric nonlinearity in lead magnoniobate ceramics doped with lithium show that at a certain value of external field amplitude E, two peaks appear on the temperature dependences of effective dielectric permittivity ɛeff′(T). They are caused by the dynamics of the polar regions in the vicinity of diffuse phase transition and by variation in their volume under the action of field E.

Diffuse scattering anisotropy and inhomogeneous lattice deformations in the lead magnoniobate relaxor PMN above the Burns temperature

Neutron diffuse scattering measurements on single crystal PbMg${}_{1/3}$Nb${}_{2/3}$O${}_{3}$ above the Burns temperature are reported. The high temperature elastic diffuse component is highly asymmetric near reciprocal lattice points not corresponding to high-symmetry directions. This asymmetry can be described using Huang scattering formalism assuming that the scattering originates from mesoscopic lattice deformations due to elastic defects. Qualitative agreement between this model and the experimental data is achieved with simple, isotropic defects. It is demonstrated that the weak satellite maxima near Bragg reflections can be interpreted in terms of a finite resolution effect.

Quantum-mechanical calculations and analysis of vibrational modes in lead magnoniobate

The vibrational modes in lead magnoniobate have been calculated using the frozen phonon method. It has been shown that lead atoms participate in two radically different vibrational modes, namely, a nonpolar antiferrodistortive mode, which involves the antiphase motion of some lead atoms with respect to other lead atoms, and a polar mode, which includes the polar motion of lead atoms with respect to other atoms of the lattice. The nontrivial properties of lead magnoniobate have been discussed in terms of the unity and conflict of these modes.

Two-mode behavior of the PbMg1/3Nb2/3O3 relaxor

The low-frequency lattice dynamics of lead magnoniobate has been studied using inelastic neutron scattering in the temperature range 650 K < T < 1050 K. The measurements have been performed in two Brillouin zones, (200) and (300). The data corresponding to these two zones and different values of the reduced wave vector have been treated in a common frame. It has been shown that the model assuming one optical phonon mode fails in an adequate description of scattering in both zones. The model involving a two-mode behavior of soft optical phonons provides a good agreement with experimental data. It has been demonstrated that the frequency of the low-energy soft-mode component follows the Curie-Weiss law with the Curie temperature TC = 400 K, which fits well dielectric spectroscopy measurements.

Photostimulated phenomena in relaxors

The action of illumination on the conducting and dielectric properties of lead magnoniobate was investigated. The photostimulated currents were examined and the spectral dependence of photoconductivity in the region of diffuse phase transition was obtained. It was found that the illumination affects the dielectric properties and that its action is memorized at temperatures below room temperature. The role of defect states in the formation of relaxor properties is discussed on the basis of the obtained data.

Potential relief on the surface of polarized ferroelectric electrets from an analysis of the anomalous electron emission spectra

A technique is proposed for determining the specific features in the potential distribution over a free surface of polarized ferroelectric electrets from analyzing the anomalous electron emission spectra. This technique is applied to examine the potential distribution over the surface of a lead magnoniobate single crystal and ferroelectric ceramics. Reasoning from the results obtained for the lead magnoniobate crystal, the inference is drawn that the degree of perfection of surface layers of ferroelectric single crystals can be controlled using the anomalous electron emission spectra.

On the kinetics of slow polarization in the lead magnoniobate ferroelectric relaxor

Polarization and repolarization of a (100)-oriented lead magnoniobate crystal in slowly varying and dc electric fields were measured in a temperature interval including the relaxor and field-induced ferroelectric states. Throughout the interval covered, the polarization was shown to exhibit features characteristic of relaxors, namely, open, nonreproducing polarization trajectories in the first few cycles of quasistatic dielectric hysteresis loops and very long relaxation times. The slow thermally activated relaxation stage follows the universal power law evolution, which permits one to determine possible simple spectra of the relaxation time distribution. Temperature dependences of some relaxation and spectral parameters were derived, and their differences in the relaxor and ferroelectric phases are discussed.

Description of ferroelectric phase transitions in solid solutions of relaxors in the framework of the random-field theory

A model based on the random-field theory is proposed for calculating the properties of solid solutions of ferroelectric relaxors. The electric dipoles randomly distributed in the system are treated as sources of random fields. The random field distribution function is calculated taking into account the contribution of nonlinear and correlation effects and the differences in the dipole orientations for different solid solution components. The dependence of the phase transition temperature Tc on the concentration of solid solution components is analyzed. Numerical calculations are performed for the lead scandoniobate and lead scandotantalate solid solutions (PbSc1/2Nb1/2O3)1−x(PbSc1/2Ta1/2O3)x with different degrees of ordering and the lead magnoniobate and lead titanate solid solution (PbMg1/3Nb2/3O3)1−x(PbTiO3)x. It is shown that the higher transition temperature for more disordered solid solutions of the composition (PbSc1/2Nb1/2O3)1−x(PbSc1/2Ta1/2O3)x in the range 0≤x<0.5 is associated with the larger nonlinearity coefficient for PbSc1/2Nb1/2O3 as compared to that for PbSc1/2Ta1/2O3. The theory provides a means for calculating the region of the coexistence of the phases with different symmetry groups in the temperature-composition phase diagram of the (PbMg1/3Nb2/3O3)1−x(PbTiO3) solid solution. Numerical calculations with the use of the fitting parameters obtained from the known transition temperatures Tc for the solid solution components adequately describe the experimental phase diagrams for the aforementioned solid solutions of ferroelectric relaxors.

Hydrothermal synthesis of lead magnoniobate powder

Lead Magnoniobate (designated as PMN) is the most promising ferroelectric relaxor material. Hydrothermal synthesis of PMN under low temperature demonstrated positive results with niobium oxide as one of the starting materials. The as-prepared nanometer crystallized pyrochlore phase can be transformed into perovskite phase by heat treatment at elevated temperatures. Both of the powders before and after heat treatment were analysed by means of X-ray diffractometry (XRD), differential thermal analysis (DTA) and X-ray photoelectron spectroscopy (XPS).