Investigation of the dielectric relaxation processes in PbZr0.65Ti0.35O3-BaFe12O19 multiferroic ceramic composites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of Fe-doping on the structural, microstructural, optical, and ferroeletric properties of Pb1/2Sr1/2Ti1-xFexO3 oxide prepared by spin coating technique

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Síntese e caracterização de filmes finos de ferrita de bismuto dopados com cálcio visando aplicação em memórias de múltiplos estados

The increasing demand for electro-electronic devices, with high performance and multi-functional and the rapid advances of the nanotechnology require the development of new methods and techniques for the production and characterization of nanostructure materials and phenomenological models to describe/to predict some of its properties. The demand for multifunctionality requires, at least, new materials, that can integrate ferroelectric and magnetic properties of high technological interest. Inside of this context, multiferroics material can be considered suitable to integrate two or more physical properties of high technological interest. It can also provides new challenges in the processes of synthesis of new materials, and development of new devices with controlling and simulation of its physical properties and modeling. For this Calcium (Ca)-doped bismuth ferrite (BiFeO3) thin films prepared by using the polymeric precursor method (PPM) were characterized by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), polarization and piezoelectric measurements.In order to study the behavior and determine which are the most important parameters to achieve the optimal property to be applied to a multiferroic materials

Synthesis and characterization of NaNbO3 mesostructure by a microwave-assisted hydrothermal method

In the present work, we report the synthesis and characterization of NaNbO3 particles obtained by microwave-assisted hydrothermal method from Nb2O5 and NaOH. The synthesis was made at different periods at 180 °C and 300W. The crystallization of NaNbO3 structures produced Na2Nb2O6.H2O in the intermediate phase with fiber-like morphology, and this is associated with the synthesis time. Pure orthorhombic NaNbO3 with cube-like morphology originates after synthesizing for 240 minutes. To verify the remnant polarization of particles, films were obtained by electrophoresis process and sintered at 800°C for 10 minutes in a microwave furnace. The films characterization indicated that films of niobate with fiber-like morphology present remaining polarization, and the morphology of cubes did not show remaining polarization. Considering these results, it can be concluded that the morphology implemented ferroelectric property of NaNbO3.

Effect of oxidizing and reducing atmospheres on Ba(Ti0.90 Zr0.10)O3:2V ceramics as characterized by piezoresponse force microscopy

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Morphological characterization by SEM, TEM and AFM of nanoparticles and functional nanocomposites based on natural rubber filled with oxide nanopowders

Nanocomposites were prepared from mixture of different concentrations of ferroelectric nanoparticles in an elastomeric matrix based on the vulcanized natural rubber. The morphological characterization of nanocomposites was carried out using Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Atomic force microscopy (AFM). The nanocrystalline ferroelectric oxide is potassium strontium niobate (KSN) with stoichiometry KSr2Nb5O15, and was synthesized by the chemical route using a modified polyol method, obtaining particle size and microstrain equal to 20 nm and 0.32, respectively. These ferroelectric nanoparticles were added into the natural rubber in concentrations equal to 1, 3, 5, 10, 20 and 50 phr (parts per hundred of rubber) forming ferroelectric nanocomposites (NR/KSN). Using morphological characterization, we identified the maximum value of surface roughness at low concentrations, in particular, sample with 3 phr of nanoparticles and factors such as encapsulation and uniformity in the distribution of nanoparticles into the natural rubber matrix are investigated and discussed.

New features of the morphotropic phase boundary in the PbZrO 3-PbTiO3 system: A Raman spectroscopy study

In this work we present a Raman study of PbZr1-xTi xO3 ceramics with composition values close to the morphotropic phase boundary region. The analysis of the Raman spectra leads to the determination of the monoclinic phase extension at different temperatures in a very good agreement with those determined by diffraction techniques. Therefore the obtained results show that Raman spectroscopy is a powerful and suitable technique to study structural phase transitions in PbZr 1-xTixO3. © 2002 Taylor & Francis.

Dielectric properties of Sr0.75Ba0.25Nb 2O6 thin films: Bias field, frequency and temperature dependence

Ferroelectric strontium barium niobate solid solutions had received great attention due to their excellent pyroelectric, electrooptic and photorefractive properties. Furthermore, they usually also present very interesting phase transition characteristics. In this work, polycrystalline single phase Sr 0.75 Ba 0.25 Nb 2 O 6 thin films were prepared by a hybrid chemical method and deposited on Pt/Ti/SiO 2 /Si substrates. The temperature dependence of dielectric constant was measured at different frequencies and bias field levels. The presence of two dielectric dispersion regions with relaxor characteristics was observed at distinct temperature ranges, corresponding to the ferro-paraelectric and to a structural phase transition at low temperatures, respectively. A specific dielectric dispersion region, associated with an incommensurate superstructure frequently observed in bulk samples, was not observed in this films probably due to their small grain sizes. © 2002 Taylor & Francis.

Estudo das propriedades físicas de sistemas ferroelétricos com estruturas tipo Aurivillius

Pós-graduação em Ciência dos Materiais - FEIS

Caracterização de filmes de BaxSr1-xTiO3 Sintetizados pelo método hidrotermal assistido por micro-ondas e depositados por eletroforese

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Crescimento epitaxial e caracterização de filmes finos: óxidos condutores e ferroelétricos preparados por deposição de solução química

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Comparison of crystalline thin poly(vinylidene (70%)–trifluoroethylene (30%)) copolymer films with short chain poly(vinylidene fluoride) films

We compare the photoemission and electron energy loss spectra of crystalline poly(vinylidene-fluoride with trifluoroethylene: 70%: 30%), P(VDF–TrFE), films, fabricated by the Langmuir–Blodgett technique and annealed in vacuum, with in situ thermally evaporated films of poly(vinylidene-fluoride) (PVDF) in vacuum. The electronic structure and vibrational modes of the short chain PVDF films compare well with the crystalline P(VDF–TrFE) films indicating that vacuum annealed films prepared ex situ are free of significant surface contamination once vacuum annealed. The electronic structure for the short chain PVDF films exhibits, however, different temperature dependence than the crystalline P(VDF–TrFE) films. PACS: 68.47.Mn; 71.20.Rv; 63.22.+m; 73.22.-f

Enhancement of Nematic Order and Global Phase Diagram of a Lattice Model for Coupled Nematic Systems

We use an infinite-range Maier-Saupe model, with two sets of local quadrupolar variables and restricted orientations, to investigate the global phase diagram of a coupled system of two nematic subsystems. The free energy and the equations of state are exactly calculated by standard techniques of statistical mechanics. The nematic-isotropic transition temperature of system A increases with both the interaction energy among mesogens of system B, and the two-subsystem coupling J. This enhancement of the nematic phase is manifested in a global phase diagram in terms of the interaction parameters and the temperature T. We make some comments on the connections of these results with experimental findings for a system of diluted ferroelectric nanoparticles embedded in a nematic liquid-crystalline environment.

Effect of pH-induced nanopowder deagglomeration on sintering, microstructure and dielectric properties of Ba0.77Ca0.23TiO3 ceramics

Ba0.77Ca0.23TiO3 ceramics were produced in this work starting from nanopowders synthesized via a polymeric precursor method. By adjusting the pH values of the precursor solutions above 7, it was possible to prepare powders weakly aggregated and with a smaller particle size, both facts which traduced into an enhanced nanopowders' sintering process at comparatively lower temperatures. Irrespective of the initial pH value, highly-dense and second phase-free ceramics were obtained following optimal sintering parameters (temperature and time) extracted from dilatometric and density measurements. By considering these and other sintering conditions, moreover, polycrystalline materials with an average grain size varying from 0.35 to 8 mm were produced, the grain growth process involving liquid phase-assisted sintering for heat treatments achieved at 1320 °C. The study of grain size effects on the ferroelectric properties of these materials was conducted, the results being discussed in the light of previous debates, including grain size-dependent degree of tetragonal distortion in such materials, as verified in this work.

Ferroelektrische Netzwerksynthese und ihre Charakterisierung

Deutsch:Diese Arbeit beschäftigt sich zum einen mit der Synthese neuer, vernetzbarer, ferroelektrischer Verbindungen, welche eine höhere spontane Polarisation und damit ein besseres Schaltverhalten nach Vernetzung aufweisen sollten. Dazu wurde in bekannte Systemen die Halogene Fluor, Chlor und Brom erfolgreich eingebaut. Desweiteren konnten neue Untersuchungmethoden für ferroelektrische, flüssigkristalline Netzwerke erfolgreich angewendet und weiterentwickelt werden. Damit gelang es z. B. neue Erkenntnisse über die elastischen Eigenschaften von LC-Elastomeren zu gewinnen, wobei es erstmalig gelang, Seifenblasen aus LC-Polymeren herzustellen und durch UV-Bestrahlung zu vernetzen. Durch die Messung des Radius in Abhängigkeit des Druckes war es möglich festzustellen, daß sich das Verhalten des Polymers, welches zunächst oberflächenspannungskontrolliert war, nach UV-Bestrahlung, in ein elastisches Verhalten änderte. Aus der Radius vs. Druckbeziehung war es möglich, Daten über die elastischen Eigenschaften zu erhalten. Die Ballone zeigten dabei typische, gummielastische Eigenschaften. Ein Einfluß der Mesophase (d.h. SA oder SC-Phase) auf die Eigenschaften der Ballone konnte dabei nicht festgestellt werden. Für die beiden hier untersuchten Systeme des inter- und intralyer vernetzbaren System konnte festgestellt werden, daß ihr elastisches Verhalten sehr ähnlich ist, ganz im Gegensatz zu den früheren elektrooptischen Untersuchungen. D. h. beide Systeme zeigten nach der Vernetzung bis auf einen Faktor 2 das gleiche elastische Verhalten. Im Gegensatz zu nematischen Elastomeren, welche am Phasenübergang zum Teil große thermoelastische Änderungen zeigen, zeigten die hier untersuchten Elastomere keine Änderung der elastischen Eigenschaften beim Phasenübergang, was sich u.a. auf die relativ hohen Vernetzungsdichten zurückführen läßt. Weiterhin wurde die Elektrostriktion in ferroelektrischen flüssigkristallinen Elastomerenfilmen untersucht, welche zu einem neuen Weltrekord des elektrostriktiven Effektes führte. Es wurden Schichtdickenänderungen von 4% bei einem angelegten Feld von 1,5 kV gemessen. Röntgenstreuexperimente an gespincoateten, vernetzten Polymerfilmen haben überdies gezeigt, daß der gemessene Effekt voll und ganz auf den elektroklinen Effekt zurück zu führen ist. Zum Schluß wurde ein neuer Weg ausgearbeitet, um flüssigkristalline Netzwerke unter Einsatz von weniger präparativer Chemie zu erhalten. Dazu wurde die Möglichkeit der Netzwerkbildung mit organischen Gelbildnern untersucht. In diesem Zusammenhang ist es erstmalig gelungen, ferroelektrische Flüssigkristalle reversibel in dem einen oder anderen Zustand orientiert zu stabilisieren, wobei beliebig oft zwischen den stabilisierten Zuständen gewechselt werden konnte.