Showing papers on "Ferroelectric ceramics published in 2004"

Room-temperature saturated ferroelectric polarization in BiFeO3 ceramics synthesized by rapid liquid phase sintering

Abstract: Single-phased ferroelectromagnet BiFeO3 ceramics with high resistivity were synthesized by a rapid liquid phase sintering technique. Saturated ferroelectric hysteresis loops were observed at room temperature in the ceramics sintered at 880 °C for 450 s. The spontaneous polarization, remnant polarization, and the coercive field are 8.9 μC/cm2, 4.0 μC/cm2, and 39 kV/cm, respectively, under an applied field of 100 kV/cm. It is proposed that the formation of Fe2+ and an oxygen deficiency leading to the higher leakage can be greatly suppressed by the very high heating rate, short sintering period, and liquid phase sintering technique. The latter was also found effective in increasing the density of the ceramics. The sintering technique developed in this work is expected to be useful in synthesizing other ceramics from multivalent or volatile starting materials.

Templated Grain Growth of Textured Piezoelectric Ceramics

Abstract: Crystallographic texturing of polycrystalline ferroelectric ceramics offers a means of achieving significant enhancements in the piezoelectric response. Templated grain growth (TGG) enables the fabrication of textured ceramics with single crystal-like properties, as well as single crystals. In TGG, nucleation and growth of the desired crystal on aligned single crystal template particles results in an increased fraction of oriented material with heating. To facilitate alignment during forming, template particles must be anisometric in shape. To serve as the preferred sites for epitaxy and subsequent oriented growth of the matrix, the template particles need to be single crystal and chemically stable up to the growth temperature. Besides templating the growth process, the template particles may also serve as seed sites for phase formation of a reactive matrix. This process, referred to as Reactive TGG (RTGG), has been used to obtain highly oriented Pb(Mg1/3Nb2/3)O3-PbTiO3, Sr0.53Ba0.47Nb2O6, and (N...

The effect of flexoelectricity on the dielectric properties of inhomogeneously strained ferroelectric thin films

Abstract: Recent experimental measurements of large flexoelectric coefficients in ferroelectric ceramics suggest that strain gradients can affect the polarization and permittivity behaviour of inhomogeneously strained ferroelectrics. Here we present a phenomenological model of the effect of flexoelectricity on the dielectric constant, polarization, Curie temperature (TC), temperature of maximum dielectric constant (Tm) and temperature of the onset of reversible polarization (Tferro) for ferroelectric thin films subject to substrate-induced epitaxial strains that are allowed to relax with thickness, and the qualitative and quantitative predictions of the model are compared with experimental results for (Ba0.5Sr0.5)TiO3 thin films on SrRuO3 electrodes. It is shown that flexoelectricity can play an important role in decreasing the maximum dielectric constant of ferroelectric thin films under inhomogeneous in-plane strain, regardless of the sign of the strain gradient.

Sodium-bismuth titanate based lead-free ferroelectric materials

Abstract: In search of lead-free ferroelectric ceramics with improved properties, an investigation was carried out on barium and strontium-modified Na0.5Bi0.5TiO3 (NBT) ceramics. Many compositions among the Ba and Sr-modified ceramic materials exhibit diffuse phase transition and are characterised by a strong temperature and frequency dispersion of the permittivity which would be connected with the cation disorder in the A site of the perovskite unit cell.

Microstructure and dielectric properties of Mg-doped barium strontium titanate ceramics

Abstract: The dielectric properties of Ba0.8Sr0.2TiO3 ceramics doped with Mg from 0.5 to 10 mol % have been investigated systematically. Two effects of Mg doping on the dielectric properties of the Ba0.8Sr0.2TiO3 ceramics have been observed. At low Mg doping concentrations (<2 mol %), Mg mainly acts as an acceptor dopant to replace Ti in the B site of ABO3 perovskite structure, leading to a shift of Curie point (TC) to lower temperatures and a diffused phase transition. The permittivity and dielectric loss are suppressed gradually as the Mg content increases and the grain size decreases drastically. At higher Mg doping concentrations (⩾2 mol %), further suppression of permittivity and losses without further TC shift are observed, which indicates a “composite” mixing effect. The grain size remains almost constant. The solubility limit of Mg in the Ba0.8Sr0.2TiO3 appears to be ∼2 mol %.

Large recoverable electrostrain in Mn-doped (Ba,Sr) TiO3 ceramics

Abstract: In this letter we demonstrate that with a different principle, BaTiO3 ceramics, so far considered as inferior piezoelectrics compared with Pb(Zr,Ti)O3 (PZT), can show a large recoverable electrostrain This principle utilizes a point-defect-mediated reversible domain switching mechanism, which can in theory generate 0368% strain for BaTiO3 ceramics at the best condition Experimental results showed that, after aging at room temperature, 10mol% Mn-doped (Ba095Sr005)TiO3 ceramics generate a large recoverable nonlinear strain of about 012%–015% at a field of 3kV∕mm This value exceeds that of conventional hard PZT piezoelectric ceramics A microscopic model for the domain-related electrostrain effect in ceramics is proposed It is also found that the large electrostrain effect is quite stable with respect to both changing frequency and fatigue cycles Large electrostrain remains recoverable down to 005Hz and after 10000cycles These results demonstrate the potential of our approach in achieving large

Non-linear constitutive modeling of ferroelectrics

Abstract: Due to the large coupling between their electrical and mechanical properties, ferroelectric ceramics are increasingly being implemented in novel devices. This review reports on recent advances in the development of predictive constitutive models for the coupled and non-linear electromechanical behavior of ferroelectrics. Such constitutive models are required to analyze the performance of ferroelectric devices and to model the failure processes in these devices and materials. The topics covered in this review include micro-electromechanical constitutive models, macroscopic phenomenological modeling for polycrystals, and the implementation of these non-linear constitutive models.

Coupled magnetodielectric properties of laminated PbZr0.53Ti0.47O3/NiFe2O4 ceramics

Abstract: Simple multiferroic laminated ceramics of lead–zirconate–titanate PbZr0.53Ti0.47O3(PZT)/NiFe2O4 were prepared by a conventional ceramic processing. The measured magnetodielectric properties demonstrated strong dependence on the relative thickness of the PZT layers, magnetic bias, and angle between the bias and polarization in the laminated ceramics. Recent theoretical approaches were employed to explain these observed behaviors. The maximum magnetoelectric sensitivity (αE31) of the ceramics samples could reach up to as high as 0.21 V/A at 11.9 kA/m. In particular, at low magnetic bias, the laminated ceramics were found to have a very large magnetoelectric sensitivity linearly varying with the bias.

Fatigue in Ferroelectric Ceramics and Related Issues

Abstract: 1 Introduction.- 2 Macroscopic Phenomenology.- 3 Agglomeration and Microstructural Effects.- 4 Acoustic Emission and Barkhausen Pulses.- 5 Models and Mechanisms.- 6 Recent Developments.- 7 Summary.- A Solutions to Integrals.- References.

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

Abstract: 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. However, after the fatigue or the depinning process, two rates of changes were noticed. Consequently, evidence of an upper-frequency limit for the coercive field changes was found. The percentage of the backswitching and its behavior for the soft PZT was almost independent of the fatigue state in the entire frequency range investigated. Nevertheless, for the hard PZT, an opposite behavior was verified. The reorientation of the domains was modeled as occurring in a viscous medium where several forces, such as viscous and restoring forces, act on them.

Ab initio studies of polarization and piezoelectricity in vinylidene fluoride and BN-based polymers.

Abstract: Highly piezoelectric and pyroelectric phases of boron-nitrogen-based polymers have been designed from first principles. They offer excellent electrical and structural properties, with up to 100% improvement in the piezoelectic response and an enhanced thermal stability with respect to polyvinylidene fluoride (PVDF). Since methods for their synthesis are readily available, these polymers are extremely promising for numerous technological applications, rivaling the properties of ferroelectric ceramics and superseding PVDF-based materials in high-performance devices.

Correlation among oxygen vacancies in bismuth titanate ferroelectric ceramics

Abstract: Pure Bi4Ti3O12 ceramics were prepared using the conventional solid-state reaction method and their dielectric properties were investigated. A dielectric loss peak with the relaxation-type characteristic was observed at about 370K at 100Hz frequency. This peak was confirmed to be associated with the migration of oxygen vacancies inside ceramics. The Cole–Cole fitting to this peak reveals a strong correlation among oxygen vacancies and this strong correlation is considered to commonly exist among oxygen vacancies in ferroelectrics. Therefore, the migration of oxygen vacancies in ferroelectric materials would demonstrate a collective behavior instead of an individual one due to this strong correlation. Furthermore, this correlation is in proportion to the concentration and in inverse proportion to the activation energy of oxygen vacancies. These results could be helpful to the understanding of the fatigue mechanisms in ferroelectric materials.

Tunability and relaxor properties of ferroelectric barium stannate titanate ceramics

Abstract: Barium stannate titanate [Ba(SnxTi1−x)O3, x=0.1, 0.2, 0.3, and 0.4] ceramics were prepared using a conventional solid-state reaction process. Their dielectric properties were measured under direct current bias fields ranging from 0to2.5kV∕cm. A transformation from normal to relaxor ferroelectrics was observed when x⩾0.3. Broken long-range order or “dirty” ferroelectric domains and nanodomains were observed in Ba(Sn0.1Ti0.9)O3 and Ba(Sn0.4Ti0.6)O3 by transmission electron microscopy, respectively. Voltage driven tunability was found to decrease with increasing Sn content. The change from normal ferroelectric into relaxor ferroelectric had a negative impact on the tunability value of the materials.

Stress effects in sol-gel derived ferroelectric thin films

Abstract: Residual stress development during processing of sol-gel derived ferroelectric thin films influences electromechanical properties and performance. The present work investigates the effects of stress on field-induced polarization switching in ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) (52/48) thin films. Film response is measured as a function of externally applied mechanical stress using a double-beam laser-Doppler heterodyne interferometer. This apparatus successfully eliminates any displacement contribution from flexural vibration of the substrate and enables measurement of the strain-electric field hysteresis loops as a function of applied stress. The field-induced strain in the PZT film increases with increasing compressive stress, while the opposite trend is observed for applied tensile stress. The dependence of electromechanical response on the external stress is attributed to the initial tensile residual stress state in the film. Tensile stress creates an in-plane clamping effect on the domains in the ...

High-pressure synthesis and ferroelectric properties in perovskite-type BiScO3–PbTiO3 solid solution

Abstract: Stabilization of a perovskite-type solid solution (1−x) PbTiO3–x BiScO3 with x⩾0.45 was demonstrated by high-pressure synthesis, and the phase diagram and the ferroelectric properties of the solid solution were investigated. The crystal symmetry of the perovskite subcell change in turn from tetragonal, to rhombohedral, to pseudocubic, to monoclinic, and then to triclinic as x increases. It was found that the tetragonal, rhombohedral, and pseudocubic phases are ferroelectric, while the monoclinic phase is not. In the morphotropic phase boundary in the vicinity of x=0.37 between tetragonal and rhombohedral phases, the maximum electromechanical coupling factor and the minimum coercive electric field were just like those observed in other Pb-based ferroelectric perovskites. In addition, relaxor behavior in the dielectric constant was observed in the vicinity of x=0.5.

Piezoelectric Properties of BaTiO3–(Bi1/2K1/2)TiO3 Ferroelectric Ceramics

Abstract: The dielectric, ferroelectric and piezoelectric properties of barium titanate (BaTiO3)-based solid solution, (1-x)BaTiO3–x(Bi1/2K1/2)TiO3 (0≤x≤1) (BT–BKT100x), a candidate lead-free piezoelectric ceramic, were studied using a starting material of fine BaTiO3 powder. The Curie temperature, Tc, of the BT–BKT ceramics shifted to higher temperatures than those of BT with increasing the amount (x) of (Bi1/2K1/2)TiO3 and Tc was higher than 200°C at x=0.2. Electromechanical coupling factor, k33, and piezoelectric constant, d33, were 0.37 and 75.8 pC/N for BT–BKT20 + MnCO3 (0.1 mass%), and 0.40 and 100 pC/N for BT–BKT5 + MnCO3 (0.1 mass%), respectively.

Microstructural studies of (PbLa)(ZrTi)O3 ceramics using complex impedance spectroscopy

Abstract: Lanthanum modified lead zirconate titanate (PLZT:8∕60∕40) ceramics prepared by a sol-gel route showed a well-defined microstructure comprising of grains separated by boundaries. Complex impedance spectroscopy has provided a convincing evidence for the existence of both grain (bulk) and grain-boundary effects that were separated in the frequency domain in impedance spectrum. The impedance analysis further provided the value of relaxation frequency, which was a characteristic intrinsic property of the material and was independent of sample geometrical factors. Relaxation frequency calculated at different temperatures was used to evaluate bulk dielectric constant (eb), which was compared with the real part of the dielectric constant (e′). The temperature variation of the bulk electrical conductivity (σdc) indicated an evidence of Arrhenius-type thermally activated process showing a linear variation up to a temperature of 713°K and was predominantly governed by grain boundary conduction showing a plateau regi...

Polar oxides : properties, characterization, and imaging

Abstract: 1 Dielectric Properties of Polar Oxides (U. Bottger).1.1 Introduction.1.2 Dielectric polarization.1.3 Ferroelectric polarization.1.4 Theory of Ferroelectric Phase Transition.1.5 Ferroelectric Materials.1.6 Ferroelectric Domains.Bibliography.2 Piezoelectric Characterization (S. Trolier-McKinstry).2.1 Important piezoelectric constants.2.2 Measurements in bulk materials.2.3 Measurements in thin films.2.4 Conclusions.Bibliography.3 Electrical Characterization of Ferroelectrics (K. Prume, T. Schmitz, S. Tiedke).3.1 Introduction.3.2 Measurement methods.3.3 Measurement types.Bibliography.4 Optical Characterization of Ferroelectric Materials (C. Buchal).4.1 Introduction: Light propagation within anisotropic crystals.4.2 The electro-optic effect.4.3 Non-linear optics.Bibliography.5 Microwave Properties and Measurement Techniques (N. Klein).5.1 Introduction.5.2 Basic relations defining microwave properties of dielectrics and normal/superconducting metals.5.3 Surface impedance of normal metals.5.4 Surface impedance of high-temperature superconductor films.5.5 Microwave properties of dielectric single crystals, ceramics and thin films.5.6 General remarks about microwave material measurements.5.7 Non resonant microwave measurement techniques.5.8 Resonator measurement techniques.5.9 Conclusions.Bibliography.6 Advanced X-ray Analysis of Ferroelectrics (K. Saito, T. Kurosawa, T. Akai, S. Yokoyama, H. Morioka, H. Funakubo).6.1 Introduction.6.2 Experimental.6.3 Results and discussion.6.4 Conclusions.Bibliography.7 Characterization of PZT-Ceramics by High-Resolution X-Ray Analysis (M. J. Hoffmann, H. Kungl, J.-Th. Reszat, S. Wagner).7.1 Introduction.7.2 Experimental.7.3 Results and discussion.7.4 Summary.Bibliography.8 In-Situ Synchrotron X-ray Studies of Processing and Physics of Ferroelectric Thin Films (G. B. Stephenson, S. K. Streiffer, D. D. Fong, M. V. Ramana Murty, O. Auciello, P. H. Fuoss, J. A. Eastman, A. Munkholm, C. Thompson).8.1 Introduction.8.2 Growth of ultrathin ferroelectric films.8.3 Observation of nanoscale 180 stripedomains.Bibliography.9 Characterization of Polar Oxides by Photo-Induced Light Scattering (M. Imlau, M. Goulkov, M. Fally, Th. Woike).9.1 Introduction.9.2 Fundamentals.9.3 Experimental.9.4 Summary.Bibliography.10 Ferroelectric Domain Breakdown: Application to Nanodomain Technology (G. Rosenman, A. Agronin, D. Dahan, M. Shvebelman, E. Weinbrandt, M. Molotskii,Y. Rosenwaks).10.1 Introduction.10.2 Nanodomain size limitations.10.3 AFM nanodomain tailoring technology.10.4 Ferroelectric domain breakdown.10.5 Nanodomain superlattices tailored by multiple tip arrays of HVAFM.10.6 Conclusions.Bibliography.11 Pyroelectric Ceramics and Thin Films: Characterization, Properties and Selection (R. W. Whatmore).11.1 Introduction.11.2 The physics of pyroelectric detectors.11.3 Measurement of physical parameters.11.4 Pyroelectricmaterials and their selection.11.5 Pyroelectric ceramics and thinfilms.11.6 Conclusions.Bibliography.12 Nano-inspection of Dielectric and Polarization Properties at Inner and Outer Interfaces in PZT Thin Films (L. M. Eng).12.1 Introduction.12.2 Methods.12.3 Materials.12.4 Results.12.5 Conclusion.Bibliography.13 Piezoelectric Relaxation and Nonlinearity investigated by Optical Interferometry and Dynamic Press Technique (D. Damjanovic).13.1 Introduction.13.2 Measurement techniques.13.3 Investigation of the piezoelectric nonlinearity in PZT thin films using optical interferometry.13.4 Investigation of the piezoelectric relaxation in ferroelectric ceramics using dynamic press.Bibliography.14 Chaotic Behavior near the Ferroelectric Phase Transition (H. Beige, M. Diestelhorst, R. Habel).14.1 Introduction.14.2 Dielectric nonlinear series-resonance circuit.14.3 Nonlinear nature of the resonant system.14.4 Tools of the nonlinear dynamics.14.5 Experimental representation of phase portraits.14.6 Comparison of calculated and experimentally observed phase portraits.14.7 Controlling chaos.14.8 Summary.Bibliography.15 Relaxor Ferroelectrics - from Random Field Models to Glassy Relaxation and Domain States (W. Kleemann, G. A. Samara, J. Dec).15.1 Introduction.15.2 Polar nanoregions.15.3 Cubic relaxors.15.4 Role of pressure.15.5 Dynamics of the dipolar slowing-down process.15.6 Uniaxial relaxors.15.7 Domain dynamics in uniaxial relaxors.Bibliography.16 Scanning Nonlinear Dielectric Microscope (Y. Cho).16.1 Introduction.16.2 Nonlinear dielectric imaging with sub- nanometer resolution.16.3 Higher order nonlinear dielectric microscopy.16.4 Three-dimensional measurement technique.16.5 Ultra High-Density Ferroelectric Data Storage Using Scanning Nonlinear Dielectric Microscopy.16.6 Conclusions.Bibliography.17 Electrical Characterization of Ferroelectric Properties in the Sub-Micrometer Scale (T. Schmitz, S. Tiedke, K. Prume, K. Szot, A. Roelofs).17.1 Introduction.17.2 Sample preparation.17.3 Contact problems.17.4 Parasitic capacitance.17.5 In-situ compensation.Bibliography.18 Searching the Ferroelectric Limit by PFM (A. Roelofs, T. Schneller, U. B ottger, K. Szot, R. Waser).18.1 Introduction.18.2 Polycrystalline ferroelectric PTO thin films on platinized silicon substrates.18.3 Separated lead titanate nano-grains.18.4 Conclusion.Bibliography.19 Piezoelectric Studies at Submicron and Nano Scale (E. L. Colla, I. Stolichnov).19.1 Introduction.19.2 Investigating cycling induced suppression of switchable polarization in FeCaps.19.3 Size effect on the polarization patterns in -sized ferroelectric film capacitors.19.3.1 Downscaling of ferroelectric capacitors.19.4 Direct observation of inversely-polarized frozen nanodomains in fatigued Fe- Caps.Bibliography.Authors.Index.

Dielectric response of the charge-ordered two-dimensional nickelate La1.5Sr0.5NiO4

Abstract: We report the dielectric response of La1.5Sr0.5NiO4, a system that experiences charge ordering above room temperature (TCO=480K) and a rearrangement of its charge-order pattern in the temperature region 160–200K. A careful analysis of the role of the electrical contacts used, sample thickness, and grain size on the experimental data allows us to determine that this material exhibits a high intrinsic dielectric constant. In addition, the temperature dependence of the dielectric constant, that shows a maximum in the region of the rearrangement of the charge-order pattern, points to a link between the two phenomena.

Relaxorlike dielectric properties and history-dependent effects in the lead-free K0.5Na0.5NbO3–SrTiO3 ceramic system

Abstract: Typical relaxorlike dielectric properties, such as broad dispersive dielectric maximum, Vogel–Fulcher temperature dependence of the characteristic relaxation frequency, and paraelectric-to-glass crossover in the temperature dependence of the dielectric nonlinearity, have been detected in the derived lead-free K0.5Na0.5NbO3–SrTiO3 ceramic system. Relatively large values of the dielectric constant, being almost independent of the frequency in the range of 100Hz–1MHz, suggest possible applications based on this environmentally friendly system. Furthermore, the history-dependent effects, such as aging of the dielectric constant and fatigue of the polarization switching, are much weaker than in some widely used lead-based relaxors.

Preparation and Characterization of Barium Titanate Suspensions for Stereolithography

Abstract: Ferroelectric photoactive suspensions for stereolithography have been developed by dispersing a high volume fraction of barium titanate powder in hexanediol diacrylate (HDDA) with the aid of effective photoinitiators and dispersants. Rheological properties showed a shear thinning behavior and a low viscosity at a shear rate adequate for the recoating process. The barium titanate–HDDA suspension showed poor curing behavior due to the large refractive index difference between the ceramic and the resin. The coarse barium titanate–HDDA suspension showed a smaller surface reflectance and a larger cure depth than the fine barium titanate–HDDA suspension.

Effects of lanthanum doping on the dielectric properties of Ba(Fe0.5Nb0.5)O3 ceramic

Abstract: The relaxor type of ferroelectric material Ba(FeNb)1∕2O3, which has a partially disordered perovskite structure, has been characterized and shown a maximum plateau of the dielectric permittivity depending upon the temperature. The dielectric constant at a low frequency is up to 30 000 at room temperature. While the single-phase La-doped Ba(FeNb)1∕2O3, Ba1−xLax(Fe1∕2Nb1∕2)1−x∕4O3(0⩽x⩽0.2) has a monoclinic structure solid solutions up to x⩽0.2, the lattice parameters decrease with an increasing La concentration. The temperature dependence of the dielectric constant of the La-doped Ba(FeNb)1∕2O3 was measured with different La contents, showing that the dielectric permittivity is higher than 105 at an 8mol% La concentration. The present dielectric dispersion was interpreted on the basis of the interfacial polarization at the grain-boundary region.

Combined effect of preferential orientation and Zr/Ti atomic ratio on electrical properties of Pb(ZrxTi1−x)O3 thin films

Abstract: Lead zirconate titanate [Pb(ZrxTi1−x)O3, PZT] thin films with various compositions, whose Zr/Ti ratio were varied as 40/60, 48/52, 47/53, and 60/40, were deposited on Pt(111)/Ti/SiO2/Si substrates by sol-gel method. A seeding layer was introduced between the PZT layer and the bottom electrode to control the texture of overlaid PZT thin films. A single perovskite PZT thin film with absolute (100) texture was obtained, when lead oxide was used as the seeding crystal, whereas titanium dioxide resulted in highly [111]-oriented PZT films. The dielectric and ferroelectric properties of PZT films with different preferential orientations were evaluated systemically as a function of composition. The maximums of relative dielectric constant were obtained in the morphotropic phase boundary region for both (100)- and (111)-textured PZT films. The ferroelectric properties also greatly depend on films’ texture and composition. The intrinsic and extrinsic contributions to dielectric and ferroelectric properties were dis...

Dielectric and pyroelectric properties of lead zirconate titanate/polyurethane composites

Abstract: 0-3 composite ranging between 0 and 3, of ferroelectric ceramic lead zirconate titanate (PZT) and thermoplastic elastomer polyurethane (PU) were fabricated. The pyroelectric and dielectric properties of the hot-pressed thin film samples of various PZT volume fractions were measured. The experimental dielectric permittivities and losses agreed reasonably well with the Bruggeman model. The room temperature pyroelectric coefficients of the composites were found to increase linearly with PZT volume fraction and substantially larger than expected. For example, for a composite with 30% PZT, its pyroelectric coefficient is about 90μC∕m2K at room temperature, which is more than tenfold of a PZT∕PVDF composite of the same ceramic volume fraction. We propose a model in which the electrical conductivity of the composite system is taken into consideration to explain the linear relationship and the extraordinarily large pyroelectric coefficients obtained.

High-frequency electron paramagnetic resonance investigation of the Fe3+ impurity center in polycrystalline PbTiO3 in its ferroelectric phase

Abstract: The intrinsic iron(III) impurity center in polycrystalline lead titanate was investigated by means of high-frequency electron paramagnetic resonance spectroscopy in order to determine the local-environment sensitive fine-structure parameter D. At a spectrometer frequency of 190GHz, a spectral analysis of a powder sample was unambiguously possible. The observed mean value D=+35.28GHz can be rationalized if Fe3+ ions substitute for Ti4+ at the B site of the perovskite ABO3 lattice forming a directly coordinated FeTi′–VO∙∙ defect associate. A consistent fit of the multifrequency data necessitated the use of a distribution of the D values with a variance of about 1GHz. This statistical distribution of values is probably related to more distant defects and vacancies.

Impedance spectroscopy of Bi4Ti3O12 ceramic produced by self-propagating high-temperature synthesis technique

Abstract: Bi 4 Ti 3 O 12 (bismuth titanate—BIT) ferroelectric ceramic was synthesized by self-propagating high-temperature synthesis (SHS) technique. The microstructure, electric and dielectric properties were determined and the results were compared to a reference sample produced by solid state reaction. The powders from SHS had agglomerated particles with average size of 200 nm. Bi 4 Ti 3 O 12 100% crystalline phase was reached after SHS reaction followed by sintering at 1050°C/2 h. The sintered bodies presented high relative density (98%) and small grain size (around 5 microns). The electrical and dielectric properties of the samples were studied using the impedance spectroscopy technique, and the three observed semicircles in the complex impedance diagrams were associated to the bulk, plate boundaries and grain boundaries of the sintered ceramics. The samples produced through SHS presented the same bulk conductivity as the reference one, and lower conductivity of the grain and plate boundaries. The same dielectric constant e ′=200, at 300 °C and f =1 MHz, was found for SHS sample and for the reference. For higher temperatures, at this same frequency, SHS samples presented higher relative permittivity than the reference, and for temperatures above T c both samples presented the same Curie–Weiss parameters. The differences observed in the electrical conductivity and relative permittivity, were attributed to the differences in the grain size and defect concentration. The anomaly in the permittivity curves near 550 °C is also discussed.

Formation of 90° elastic domains during local 180° switching in epitaxial ferroelectric thin films

Abstract: 90° elastic domains were observed after local polings in epitaxial ferroelectric Pb(Zr0.2Ti0.8)O3 thin films via piezoresponse force microscopy. An area of internal stress arises under a conductive atomic force microscope tip due to the opposite signs of the converse piezoelectric effects in the switched domain and the unswitched films surrounding. The formation of 90° domains leads to the relaxation of the internal stress and stabilization of 180° domain after turning off the electric field applied by the tip. The criterion that formulates the necessary condition for realization of the relaxation mechanism is presented as well.