A. Peláiz-Barranco

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.

Piezo-, pyro-, ferro-, and dielectric properties of ceramic/polymer composites obtained from two modifications of lead titanate

Two modifications of lead titanate ceramic and the polyetherketoneketone polymer (PEKK) have been used to obtain two polymer/ceramic composites. The piezo-, pyro-, ferroelectric, and dielectric properties were studied. The calcium modified lead titanate/polyetherketoneketone (PTCa/PEKK) composite shows better piezo- and pyro-electric properties than that of the samarium and manganese modified lead titanate/polyetherketoneketone (PSTM/PEKK) composite. Also, a lower dielectric permittivity and remanent polarization values with a higher coercive field are obtained. The results are discussed considering the modifications made in the ceramic phases of each composite. The presented properties for both composites are still substantially lower than those in bulk ceramics.

Dielectric relaxation and conductivity behavior in modified lead titanate ferroelectric ceramics

The frequency and temperature dielectric response and the electrical conductivity behavior around the ferroelectric–paraelectric phase transition temperature are studied in the ferroelectric ceramic system (Pb0.88Sm0.08)(Ti1−xMnx)O3, with x = 0,1,3 at.%. The contribution of the conductive processes to the dielectric relaxation for the studied frequency range is discussed considering the oxygen vacancies as the most mobile ionic defects in perovskites, whose concentration seems to increase with the manganese content. The relaxation processes below the transition temperature are associated with the decay of the polarization in the oxygen-defect-related dipoles due to their hopping conduction. Above the ferroelectric–paraelectric phase transition temperature, the electrical conduction is governed by the thermal excitation of carriers from oxygen vacancies; the relaxation processes are associated with ionic dipoles distorted by the oxygen vacancies.

Domain structures and nanostructures in incommensurate antiferroelectric PbxLa1−x(Zr0.9Ti0.1)O3

The details of the domain structure of the incommensurate antiferroelectric structure in La-doped zirconium-rich lead zirconate titanate have been revealed in detail for the first time. The structure is dominated by 60° domain boundaries close to {101} planes of the primitive perovskite cell; and tilts of the perovskite sublattice of about 0.5° are also noted at such boundaries consistent with a small tetragonal distortion of the primitive cell. Within each domain a streaked nanostructure is revealed under weak diffraction conditions perpendicular to the long b-axis of the incommensurate supercell, which appears to be a consequence of planar faulting perpendicular to this b-axis. 90° domain boundaries are also observed but are less frequent than 60° boundaries and in contrast to previous reports, these often have rather curved and irregular boundary planes. The close similarity of all these features, with the one exception of the streaked nanostructure, to the domain structure of the commensurate antiferr...

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.

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.

Dielectric Relaxation Mechanisms in Relaxor Bi-Layered Perovskites

Sr1-xBaxBi2Nb2O9 (x = 50 and 90 mol%) ferroelectric bi-layered perovskites exhibit a complex dielectric response, showing typical relaxor behavior with strong dispersion of the dielectric permittivity. The Cole-Cole model describes the relaxation processes. Two relaxation processes are analyzed considering: i) the relaxor-like ferroelectric behavior, resulting from the inhomogeneous distribution of barium due to its preference for the bismuth site in the (Bi2O2)2+ layers, and ii) the interaction between the dipoles, which form the microdomains above the relaxor ferroelectric peak, and the electrons, which are due to the ionization of the oxygen vacancies.

Domain Structure in Relaxor PLZT Ceramics

This paper presents the study of ceramic Pb1-3x/2 Lax (Zr1-y Tiy)O3, x/80/20 and x/70/ 30 solid solutions, where x = 6, 8 and 10%, which show a relaxor behavior with diffuse phase transition. It was possible to observe clusters of nanoregions characteristic of relaxors by means of polarized light microscopy using a lambda plate, which improves the birefringence of phases present in ceramic solid solutions. The structure pattern of clusters clearly shows two interference colors, which could be associated to tetragonal and rhombohedral distortions of perovskite unit cell, typical for compositions in the boundary region.

Pyroelectric behavior and thermally stimulated processes in niobium modified lead zirconate titanate ferroelectric ceramics

The thermally stimulated processes in niobium modified lead zirconate titanate ferroelectric system are analyzed from the thermally stimulated depolarization current. Different theoretical models are considered to evaluate the i-T experimental data. The results are associated with the space charge, the pyroelectric response, and the electrical conduction mechanism related to the oxygen vacancies. The results for the pyroelectric contribution are discussed considering the niobium concentration.

Study of incommensurate phases in Lanthanum-doped zirconium-rich Lead Zirconate Titanate ceramics

The microstructure and nanostructure of zirconium-rich Pb(Zr,Ti)O3 ceramics doped with small amounts of La which are right at transition between the ferroelectric (FE) and antiferroelectric (AFE) orderings has been examined using Transmission Electron Microscopy (TEM) imaging and diffraction. In this region, the La doping frustrates the formation of simple FE or AFE phases and promotes long period ordered phases (2-3 nm) with ordering along with unit cells incommensurate with the primitive cubic unit cell. We show that the domain structure in these materials is closely related to that previously observed in AFE PbZrO3. Moreover, precision measurements of crystallographic tilts at domain boundaries using Kikuchi diffraction methods also confirms the close relationship to PbZrO3. The domains also contain a nanostructure perpendicular to the long-period ordering direction, but the reasons for the appearance of this nanostructure remain unclear.