J. D. S. Guerra

Ionized oxygen vacancy-related electrical conductivity in (Pb 1−x La x ) (Zr 0.90 Ti 0.10 ) 1−x/4 O 3 ceramics

The electrical conductivity behaviour in the paraelectric state has been investigated in lanthanum modified lead zirconate titanate (PLZT) ceramics, considering the universal relaxation law. The contribution of conductive processes to the dielectric response for the low-frequency range was discussed taking into account the oxygen vacancies mechanism. The activation energies for the thermally hopping and conductivity processes were obtained. The results for the frequency dependence of the conductivity suggest at the oxygen vacancy hopping processes, due to relaxations in oxygen vacancy-related dipoles, being mainly responsible for the conduction behaviour in the studied system.

Evidence for the monoclinic-tetragonal phase coexistence in Pb(Zr0.53Ti0.47)O3 thin films

The structure and ferroelectric properties of PbZr0.53Ti0.47O3 thin films were investigated in detail by using the x-ray diffraction technique. The surface morphology of the film was studied by using the atomic force microscopy technique, showing a film with a dense morphology and a smooth surface. Based on recent results reported by Pandey et al (2008 Acta Crystallogr. A64 192), Rietveld refinements of the structure were conducted considering different models proposed in the literature. Results suggested the monoclinic and tetragonal (M+T) phase coexistence, with P4mm and Cm space groups, respectively. The monoclinic phase (68 mol%) is dominant over the tetragonal phase (32 mol%) for this PZT film composition.

Multiferroism and magnetoelectric coupling in (PbZr0.65Ti0.35O3)0.97–(BaFe12O19)0.03 ceramic composites

The ferroelectric, magnetic, and magneto-electric properties of a PZT/Ba-hexaferrite (PbZr0.65Ti0.35O3/BaFe12O19) ceramic composite are reported. The expected rhombohedral-PZT and Ba-hexaferrite phases have been confirmed from structural and Rietveld refinement analyses, without additional undesired phases. Well-saturated ferroelectric and magnetic hysteresis loops confirmed the ferroelectric and magnetic nature of the study system, revealing enhanced characteristics when compared to those reported for typical multiferroics. The existence and enhancement of the magneto-electric response have been demonstrated by measuring the effect of the external DC magnetic field on the dielectric permittivity. The obtained results suggest an excellent candidate for room temperature multiferroic system with enhanced properties.

Domain wall contribution to dielectric and piezoelectric responses in 0.65Pb(Mg1/3Nb2/3)–0.35PbTiO3 ferroelectric ceramics

In this paper, the contribution of the domain walls motion to the dielectric and piezoelectric responses for the 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 system is investigated. A monotonically increasing temperature dependence of the dielectric permittivity is observed from very low temperatures up to the ferroelectric–paraelectric phase transition temperature. It is verified that the major contribution to dielectric response at room temperature is from the extrinsic effect. A linear dependence of the permittivity with the amplitude of the ac applied electric field is verified from the nonlinear dielectric measurement. Rayleighs model is used to quantitatively evaluate the dielectric response, leading to similar behaviour of the typical soft PZT. On the other hand, direct piezoelectric response also displays a Rayleigh-type behaviour. Piezoelectric measurements show in the entire investigated dynamic stress range a decrease in the piezoelectric response with both increase in frequency of the applied dynamic stress and increase in the pre-stress on the samples.

Modeling the dielectric response of lanthanum modified lead zirconate titanate ferroelectric ceramics-an approach to the phase transitions in relaxor ferroelectrics

The relaxor behavior of lanthanum modified lead zirconate titanate (PLZT) ferroelectric ceramics, for a La/Zr/Ti ratio of x/60/40, has been analyzed. An approximation to the dynamical behavior of the polar nano-regions (PNRs) has been discussed, taking into account a relaxation model, which considers a distribution function for the relaxation times. A good agreement between theoretical and experimental results was obtained. The behaviors of the mean relaxation time and its standard deviation with temperature were discussed, considering the correlation between the polar nano-regions and the freezing temperature. The temperature dependence of the polarization showed an anomalous behavior around a temperature, which was associated with the freezing temperature, according to the proposed model in the present work.

High frequency dielectric relaxation in lanthanum modified PbTiO3 ferroelectric ceramics

Dielectric measurements of lanthanum modified lead titanate ceramics were carried out in a frequency and temperature range of 70 ´ 106Hz - 2 ´ 109Hz and 300 K - 420 K, respectively. Dielectric relaxation appears around 7 ´ 108Hz at room temperature, and the maximum of the dielectric relaxation was around 393 K, the transition temperature (Tc). The relaxation frequency passes through a minimum at Tc and the dielectric relaxation exists in both paraelectric and ferroelectric phases. A fitting of the experimental data with the Debye relations gives some keys for understanding the dielectric behavior of such materials.

The pyroelectric behavior of lead free ferroelectric ceramics in thermally stimulated depolarization current measurements

The present paper shows a detailed analysis on the thermally stimulated processes in barium modified SrBi2Nb2O9 ferroelectric bi-layered perovskite, which is one of the most promising candidates for non-volatile random access memory applications because of its excellent fatigue-resistant properties. A numerical method is used to separate the real pyroelectric current from the other thermally stimulated processes. A discharge due to the space-charge injected during the poling process, the pyroelectric response, and a conductive process are discussed in a wide temperature range from ferroelectric to paraelectric phase. The pyroelectric response is separated from the other components to evaluate the polarization behavior and some pyroelectric parameters. The remanent polarization, the pyroelectric coefficient, and the merit figure are evaluated, which show good results.

Synthesis and Electrical Properties of PZT/BaFe12O19 Multiferroic Ceramics

Multiferroic ceramics, based on the ferroelectric and ferrimagnetic phases of the Pb(Zr0.65Ti0.35)O3 (PZT) and BaFe12O19 (BaM) systems, respectively, were obtained from the conventional ceramic method. The electrical properties have been investigated in a wide temperature and frequency range. The influence of the magnetic phase on the ferroelectric and dielectric properties of the ferroelectrics phases have been taken into account. The phase transition characteristics shown to be strongly affected by the amount of the BaM phase, while the dielectric properties revealed to be directly dominated by the presence of conductive effects related to the charge transport mechanisms associated to the magnetic phase.

Effect of the sintering conditions on the electrical properties of Nd3+ modified PLZT ceramics

The effect of the sintering method on the microstructural and electrical properties of (Pb0.89Nd0.02La0.09)(Zr0.65Ti0.35)O3 (PNLZT) ceramics was studied by impedance spectroscopy. Structural and microstructural analyses were performed using x-ray and scanning electron microscopy techniques. Two different sintering routes were employed: the conventional and the hot-pressing sintering methods. The impedance analysis provided a convincing evidence for the existence of both grain (g) and grain boundary (gb) contributions to the conduction process. An equivalent circuit for the impedance behaviour has been proposed and discussed. The variation in the sintering method produces significant changes in the grain and grain boundary conductivities. For the grain effect, the main conduction mechanism has been associated with oxygen vacancy migration. Otherwise, for grain boundary conductivity the impedance behaviour has been discussed in terms of the brick-layer and the constriction resistance models (BLM and CRM, respectively).

Photoluminescence in Pb0.95Sr0.05(Zr1−xTix)1−yCryO3 ferroelectric ceramic system

Over the past several years, there has been a remarkable growth and development in new ceramic and/or composite materials to be used in the electro-electronic industry. Ferroelectric materials have been recognized for their multifunctional physical properties; also, their optical properties are a subject of intense research effort due to their possible electro-optic applications. In this work, the visible photoluminescence effect is analyzed at room temperature in a sintered Pb0.95Sr0.05(Zr1−xTix)1−yCryO3 perovskite-type structure system, doped with Sr and Cr. The excitation bands used were 267, 325, 373, 457, 635, and 680 nm, but the best result was obtained at 373 nm. The intensity and energy of such emission in this system have been studied by changing the molar Cr concentration (0 < y < 0.005) and the Ti content (x), with x = 0.20, 0.40, 0.53, 0.60, and 0.80, on both sides of the morphotropic phase boundary (MPB) zone. The principal emission bands are at the energies 1.73, 1.87, and 3.03 eV. The chang...