M. H. Lente

90° domain wall relaxation and frequency dependence of the coercive field in the ferroelectric switching process

The mechanisms involved in the polarization switching process in soft and hard Pb(Zr53,Ti47)O3 (PZT) bulk ceramics were investigated through the dependency of the hysteresis loop on the frequency. In order to determine the influence of the defects on the domain switching dynamics, the samples were characterized in the virgin state and after a fatigue or a depinning process. The frequency dependence of the polarization revealed a strong relaxation of the 90° domain walls at ∼100 Hz. The results also revealed a strong influence of the kind of defect and their distribution in the ferroelectric matrix on the domain switching dynamics, which were reflected in the frequency dependence of the coercive field and the percentage of the backswitching. Initially, it was observed that the frequency dependence of the coercive field for the soft and the hard PZT in the virgin state had just one rate of change per decade in the entire frequency range investigated, which is the standard behavior found in the literature. H...

Microwave dielectric dispersion process in perovskite ferroelectric systems

The microwave dielectric dispersion process was investigated in relaxor and normal ferroelectric compositions of Pb1−xLaxTiO3 ceramics. The results revealed the following remarkable features: (i) the mechanism responsible for the microwave dielectric dispersion process in perovskite ferroelectric systems may be associated to the vibration of the boundaries of polar regions, independently of their size and dynamical properties; (ii) the characteristic frequency, fR, is governed by the ratio between the force constant and the effective mass of such boundaries; (iii) the temperature dependence of fR above the temperature of the maximum of the dielectric permittivity directly reflects the ferroelectric-type phase transition.

Hot-pressed transparent PLZT ceramics from low cost chemical processing

Lanthanum-modified lead zirconate titanate (PLZT) ceramics were obtained with high transmittance in the visible range by a combination of an inexpensive chemical processing and hot pressing. Optical, microstructural, pyroelectric, ferroelectric and dielectric properties characterized in this study attested the applicability of the employed method in the production of PLZT transparent ferroelectric ceramics. In fact, the corresponding analyzed physical parameters are in very good agreement with those obtained in samples traditionally prepared by other methods. Furthermore, due to high sample quality, a phenomenological analysis of the PLZT 10/65/35 relaxor features was performed in these ceramics.

X-ray powder diffraction structural characterization of Pb1 − xBaxZr0.65Ti0.35O3 ceramic

The structure of Pb(1-x)Ba(x)Zr(0.65)Ti(0.35)O(3) (PBZT) ceramic materials with 0.00 < or = x < or = 0.40 was studied using synchrotron X-ray powder diffraction data. According to the Rietveld refinements, the structure of PBZT ceramics with x = 0.00, 0.10 and 0.20 at room temperature was rhombohedral R3c. A phase transition from rhombohedral to cubic was observed at 543 and 463 K for x = 0.10 and 0.20, respectively. The refinement for the compositions x = 0.30 and x = 0.40 showed a cubic structure from 10 to 450 K, in good agreement with the dielectric properties of these samples.

Effect of the composition and sintering process on the electrical properties in Pb(Mg1/3 Nb2/3)O3–PbTiO3 ceramics

Abstract The effects of the composition and the sintering process on the ferroelectric, dielectric and electromechanical properties in (1–x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 ceramics with 0.1⩽x⩽0.4 were investigated. It was found that the densification process was strongly dependent on the amount of PT. For the lowest concentration of PT the microstructure of the both hot-pressed and conventional sintered samples were very similar, reflecting in almost identical electrical properties. Nevertheless, it was noticed that the higher amount of PT higher was the deviation of the electrical properties between the conventional and the hot-pressed samples. The gradual decreasing of the physical properties of the conventional sintered ceramics was related to the gradual decrease of the density and inhomogeneous microstructure. The results also revealed that for the lower concentration of lead titanate a relaxor behavior is noticed with a high electrostrictive effect, which was almost hysteretic free. However, higher amount of lead titanate led to a “normal” ferroelectric behavior.

Investigation of dielectric anomalies at cryogenic temperatures in (1−x)[Pb(Mg1∕3Nb2∕3)O3]–xPbTiO3 system

Complex electrical permittivity measurements in (1−x)[Pb(Mg1∕3Nb2∕3)O3]–xPbTiO3 ceramics for 0.10⩽x⩽0.40 were performed in the frequency and temperature range from 1to100kHz and from 15to600K, respectively. Unexpected dielectric anomalies, which were frequency dependent, were found at cryogenic temperatures. It was verified that this dielectric behavior is always observed, independent of whether the composition presents a “normal” ferroelectric or a relaxor characteristic. The results were analyzed within the framework of two current models found in the literature. It was concluded that none of the proposed mechanisms uniquely satisfies the experimental results in the composition range investigated here.

Temperature coefficient of piezoelectric constants in Pb(Mg1/3 Nb2/3)O3 - PbTiO3 ceramics

In this work, the thermal stability of piezoelectric constants of PMN-PT ceramics in the tetragonal and rhombohedral phases were investigated in a wide range of temperatures. The results showed that the tetragonal PMN-PT presented higher thermal stability and, consequently, the temperature coefficients for the piezoelectric constants were approximately zero. This result revealed to be much better than that commonly found for PZT ceramics. Although the rhombohedral PMN-PT presented a slight lower thermal stability, the values found for the coupling factor were significantly higher than the tetragonal composition.

Ferroelectric Domain Dynamics in PMN-PT Ceramics

The polarization switching process was investigated in PMN-PT ceramics through the frequency dependence of the hysteresis loops and the electric field induced-strain measurements. In order to investigate the influence of the ferroelectric phase on the domain reorientation process, PMN-PT ceramics with rhombohedral and tetragonal symmetries were studied. The higher coercive field observed in the tetragonal composition was associated with a higher lattice distortion. The results suggested that the ceramic with rhombohedral symmetry presents a higher collective reorientation of the domains than the tetragonal one. The reorientation of the domains was modeled as occurring in a viscous medium where several resistance forces such as viscous force and restoring forces act on them. The coercive field was interpreted as an effective field necessary to overcome these resistance forces.

Anelastic and Dielectric Characterization of Pb(Fe0.50Nb0.50)O3 Multiferroic

Magnetoelectric coupling in multiferroics materials remains as an interesting subject from fundamental as well as technological point of view, and in many cases is mediated via lattice strain. Therefore, anelastic measurements can be a powerful procedure to better understand this phenomenon. In this work, as fired Pb(Fe 0.50 Nb 0.50 )O 3 ceramics were investigated through dielectric and ultrasonic techniques in temperature range from 15 K to 450 K. The anelastic experimental results present anomalies (additional to those related to the ferroelectric (T C ) and antiferromagnetic (T N ) ordering), which could be associated with not reported ferroelectric-ferroelectric (T∼ 315 K) and an antiferromagnetic-ferromagnetic phase transitions (110 K), respectively.

Structural Characterization of Pb1−xBaxZr0.65Ti0.35O3 Ferroelectric Ceramics

In this work, X-ray absorption near edge structure (XANES) and X-Ray Diffraction (XRD) have been used to characterize, respectively, the short and long range-order structure of Pb1− xBaxZr0.65Ti0.35O3 ceramics for 0.0 ≤ x ≤ 0.40. According to XRD-Rietveld refinements, a gradual rhombohedral to cubic like-phase transition occurs with increasing barium content. It is verified that the rhombohedral structural model fits well with the lower barium-content samples, while for the highest barium-content sample (x = 0.40) the fitting parameters obtained for the cubic phase is significantly better. The XANES measurements indicated that the local structure around Ti remains distorted for all barium concentrations, thus suggesting that the local structure of PBZT is weakly dependent on the crystallographic phase.