E. I. Sitalo

Bias Field Effect on the Dielectric and Pyroelectric Response of Pb(Fe0.5Ta0.5)O3 Relaxor Multiferroic Ceramics

Dielectric and pyroelectric studies of PbFe0.5Ta0.5O3 ceramics have been carried out under different bias field values. E,T-phase diagram has been constructed using these data. It has been found out that PbFe0.5Ta0.5O3 combines the properties of both relaxors and usual ferroelectrics. The results obtained show that the origin of the relaxor-like behavior in PbFe0.5Ta0.5O3 seems to be somewhat different as compared to canonical relaxors.

Bias Field Effect on Dielectric and Pyroelectric Properties of (1-x)Pb(Fe1/2Nb1/2)O3–xPbTiO3 Ceramics

Dielectric, X-ray, pyroelectric and piezoelectric studies of the (1-x)PbFe1/2Nb1/2O3–(x)PbTiO3 ceramics from the 0 ≤ x ≤ 0.2 range fabricated by solid state synthesis and usual sintering have been carried out. In PbFe1/2Nb1/2O3 and compositions with low Ti content anomalies of dielectric, pyroelectric and piezoelectric parameters, corresponding to the transition between two ferroelectric phases have been observed at 85–90°C. A dramatic effect of bias field on dielectric and pyroelectric responces was revealed.

Piezoelectric Properties of PbFe1/2Nb1/2O3–PbTiO3 Ceramics from the Morphotropic Phase Boundary Compositional Range

Dielectric, X-ray, and piezoelectric studies of highly-resistive Li-doped (1-x)PbFe1/2Nb1/2O3–(x)PbTiO3 (PFN-xPT) ceramics from the 0 ≤ x ≤ 0.2 range fabricated by solid state synthesis and usual sintering have been carried out. Distinct anomalies of dielectric and piezoelectric parameters, corresponding to the transition between rhombohedral (monoclinic) and tetragonal ferroelectric phases have been observed in pure PbFe1/2Nb1/2O3 and PFN-xPT compositions with PbTiO3 content up to 8 mol.%. x,T-phase diagram of the PFN-xPT solid solution system have been constructed using these data.

Modeling of Piezoelectric Properties of 0.67PMN-0.33PT Ceramics with Different Degree of Texturing

Modeling of dielectric, piezoelectric, and elastic properties of 0.67PMN-0.33PT ceramic composition with different degree of texturing has been carried out within the effective media approach. The full sets of dielectric, piezoelectric, and elastic coefficients have been calculated for various distributions of crystallites orientations using the data for single domain crystals and crystals with the engineered domain structure. It is shown that maximal values of piezoelectric properties exhibit the texture, in which the polar axes of all crystallites with pseudotetragonal symmetry are oriented in the direction corresponding to the [001] direction of the prototype perovskite cubic unit cell.

Dependences of the dielectric and pyroelectric properties of (1 − x)PbFe1/2Nb1/2O3−xPbTiO3 ferroelectric ceramics solid solutions on the PbTiO3 content in a compositional range of 0 ≤ x ≤ 0.08

Abstract(1 − x)PbFe1/2Nb1/2O3−xPbTiO3 (PFN-xPT) ferroelectric ceramics with low dielectric loss and pronounced anomalies of dielectric and pyroelectric properties near the ferroelectric-ferroelectric phase transition was obtained by doping with lithium. The temperature dependence of the position of the morphotropic boundary between the rhombohedral (monoclinic) and tetragonal phases in the x-T phase diagram of the PFN-xPT system was determined for the first time.

X-ray and dielectric studies of hot-pressed K2Sr4Nb10O30 ceramics

ABSTRACT X-ray diffraction (XRD) and dielectric studies of dense hot-pressed K2Sr4Nb10O30 ceramics with a tetragonal tungsten bronze–type structure revealed texturing of the samples and substantial anisotropy of the dielectric permittivity. XRD studies of the K2Sr4Nb10O30 powder show a diffuse phase transition in the 140 – 160°C range while a diffused and frequency-independent maximum of the dielectric permittivity is observed at about 120–125°C for ceramic samples. Substantial anisotropy of the dielectric permittivity (more than 50% in the phase transition region) as well as samples texturing and a difference between phase transition temperatures of the powder and ceramic samples are supposed to be caused by anisotropic residual stresses.

Ferroelectric and magnetic phase transitions in multiferroic PbFe 0.5 Ta 0.5 O 3 -PbTiO 3 solid solutions

Dielectric, X-ray, piezoelectric and Mossbauer studies of highly-resistive Li-doped (1-x)PbFe_0.5Ta_0.5O₃-(x)PbTiO₃ ceramics from the 0<; x <;0.3 range fabricated by solid state synthesis and usual sintering have been carried out. Addition of PbTiO₃ to PbFe_0.5Ta_0.5O₃ increases the temperature T_m of the permittivity maximum, decreases the diffusion of this maximum and lowers the Neel temperature T_N. However above a certain compositional threshold fast lowering of T_N stops and a new magnetic state with comparatively high (~50 K) transition temperature becomes stable in a rather wide compositional range.

The effect of bias field on the value and temperature dependence of the piezoelectric coefficient d31 in (1 − x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (x = 0.06, 0.13) single crystals

It is established that, as a result of application of even a small (∼0.5 kV cm−1) bias field E, the maximum of the piezoelectric coefficient d31 in (1 − x)Pb(Mg1/3Nb2/3)O3 − xPbTiO3(x = 0.06, 0.13) crystals shifts from the Vogel-Fulcher temperature to the critical point in the E-T phase diagram of a given composition. The field dependence of the d31(T) peak magnitude has a maximum near the E values corresponding to the critical point.

The local cationic configurations in the K2Sr4Nb10O30 lattice and peculiarities of its surface piezoresponse

ABSTRACT Basing on the X-ray diffraction studies, a possibility of six local cationic configurations was established for K2Sr4Nb10O30 (KSN) having a tetragonal tungsten bronze-type structure. The association of these locally charged configurations may lead to the formation of the electrically active nanoregions. The piezoresponse force microscopy studies revealed at the KSN surface the presence of a subsystem of nano- or meso-size regions, which may be electrically active. Distribution and reference size of these regions have been estimated using the Fourier filtering of the source piezoresponse image.

Structure and Properties of Ferroelectric Materials after Mechanoactivation

The mechanoactivation of ferroelectric materials with perovskite structure is performed. Structural changes of the ferroelectric materials after mechanoactivation based on X-ray absorption spectra (XAFS) and X-ray diffraction data (XRD) are studied. The Fourier analysis of EXAFS spectra allows quantitative estimates to be obtained for the local atomic structure of the investigated materials after activation. The effect mechanoactivation has on permittivity in a wide range of frequencies and temperatures is considered.