Synthesis, ferroelectric and optical properties of (Pb,Ca)TiO3 thin films by soft solution processing

Calcium modified lead titanate sol was synthesized using a soft solution processing, the so-called polymeric precursor method. In soft chemistry method, soluble precursors such as lead acetate trihydrate, calcium carbonate and titanium isopropoxide, as starting materials, were mixed in aqueous solution. Pb0.7Ca0.3TiO3 thin films were deposited on platinum-coated silicon and quartz substrates by means of the spinning technique. The surface morphology and crystal structure, dielectric and optical properties of the thin films were investigated. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 299 and 0.065, respectively, for a thin film with 230 nm thickness annealed at 600degreesC for 2 h. The remanent polarization (2P(r)) and coercive field (E-c) were 32 muC/cm(2) and 100 kV/cm, respectively. Transmission spectra were recorded and from them, refractive index, extinction coefficient, and band gap energy were calculated. Thin films exhibited good optical transmissivity, and had optical direct transitions. The present study confirms the validity of the DiDomenico model for the interband transition, with a single electronic oscillator at 6.858 eV. The optical dispersion behavior of PCT thin film was found to fit well the Sellmeir dispersion equation. The band gap energy of the thin film, annealed at 600degreesC, was 3.56 eV. The results confirmed that soft solution processing provides an inexpensive and environmentally friendly route for the preparation of PCT thin films.

Influence of Ca concentration on the electric, morphological, and structural properties of (Pb,Ca)TiO3 thin films

Pb1-xCaxTiO3 (0.10less than or equal toxless than or equal to0.40) thin films on Pt/Ti/SiO2/Si(100) substrates were prepared by the soft solution process and their characteristics were investigated as a function of the calcium content (x). The structural modifications in the films were studied using x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate a decrease in lattice tetragonality with the increasing content of calcium in these films. Raman spectra exhibited characteristic features of pure PbTiO3 thin films. Variations in the phonon mode wave numbers, especially those of lower wave numbers, of Pb1-xCaxTiO3 thin films as a function of the composition corroborate the decrease in tetragonality caused by the calcium doping. As the Ca content (x) increases from 0.10 to 0.40, the dielectric constant at room temperature abnormally increased at 1 kHz from 148 to 430. Also calcium substitution decreased the remanent polarization and coercive field from 28.0 to 5.3 muC/cm(2) and 124 to 58 kV/cm, respectively. These properties can be explained in terms of variations of phase transition (ferroelectric-paraelectric), resulting from the substitution the lead site of PbTiO(3)for the nonvolatile calcium. (C) 2002 American Institute of Physics.

Effects of thermal annealing on the semi-insulating properties of radio frequency magnetron sputtering-produced germanate thin films

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Leakage current, ferroelectric and structural properties in Pb(1-x)Ba(x)TiO(3) thin films prepared by chemical route

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

Investigation of Ferroelectric Layered Perovskite Barium Bismuth Tantalate Prepared by Solid-State Reaction

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

Contribution of an extrinsic mechanism for the electrical polarization in BiMn2O5 ceramics

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

Effect of magnesium on the properties of LiNbO 3 thin films prepared from polymeric precursors

The effect of magnesium addition on the phase formation, microstructure and electric and ferroelectric properties of LiNbO 3 thin films prepared through polymeric precursors was analyzed. By X ray diffraction no secondary phase was observed with the increase of magnesium concentration. Comparing to pure LiNbO 3, the addition of 0.5 and 1.0 mol% of Mg +2 increased of the dielectric constant, while 2.0 mol% decreased it. It was noticed that the increase in additive concentration decreases the ferroelectric remanent polarization and increases the coercive field. © 2002 Taylor & Francis.

Estudio de PMN cerámico dopado con KNbO3 y LiNbO 3 sintetizado por Pechini

PMN belongs to a special class of materials named relaxor ferroelectrics. It has high volumetric efficiency due to its high dielectric constant, which makes it in a perfect material for application in multilayer capacitors. When prepared the columbite route its preparation has many advantages. In this work, the preparations of columbite and PMN were done by Pechini and Partial Oxalate methods, respectively. The effects of the KNbO3 and LiNbO3 dopants added in various concentrations. The idea is founded on the correlations that they have with BaTiO3 y PbTiO3, respectively. The whole process was supervised by TG/DTA, XRD, SEM and determination of the specific surface area of the powders. LiNbO3 carries out the pre-sinterization of the particles, observed by a reduction in the surface area. There are not particle grow, but occur its lengthening. However, for KNbO3 these particle growth, but the agglomerates are softer. The effect produced by the doping during the synthesis of the PMN powder is different from the one produced in the columbite precursor. Pure precursor shows an average particle size of 0,2μm, but the addition of 5,0mol% of dopants carries out the formation of agglomerates close to 4μm. LiNbO 3 addition carries out spherical particles and pre-sinterization, while KNbO3 addition does not change the particles shape.

The influence of the sintering system on PMN properties

PMN powder samples with PbO excess of 0, 1,2 and 3% were submitted to the pressing and sintering at 1200°C for 4h with a heating rate of 3°C/min. A new sintering system, developed at our laboratories, was used. It allows obtaining more information on the sintering process. The sintered samples in the new system were compared to sintered samples in the C system. The microstructure, dielectric properties and the effect of the PbO excess in different sintering systems were compared. The N system permitted to obtain a ceramic with better properties, such density, dielectric constant and very homogeneous microstructure.

Influence of oxygen atmosphere on LiNbO3 thin films prepared by Pechini process

Thin films of lithium niobate were deposited on the Pt/Ti/SiO2 (111) substrates by the polymeric precursor method (Pechini process). Annealing in static air and oxygen atmosphere was performed at 500°C for 3 hours. The films obtained were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The dielectric constant, dissipation factor and resistance were measured in frequency region from 10 Hz to 10 MHz. Electrical characterizations of the films pointed to ferroelectricity via hysteresis loop. The influence of oxygen atmosphere on crystallization and properties of LiNbO3 thin films is discussed.

Development of a new TDR probe for determining soil water content and dry density

A few traditional methods for determining water content in the field are either inaccurate or time consuming. As an alternative, the time domain reflectometry (TDR) technology has been used in the determination of the soil water content for geotechnical applications. This paper presents the preliminary results on the development of a new TDR probe for determining soil water content and dry density at different depths. This new probe is intended to be pushed into the ground using piezocone equipment. Different from the standard TDR probes with straight rods, the new probe consists of two parallel copper stripes coiled around a PVC-steel core. The probe diameter is the same as the standard 10 cm2 piezocone diameter. Through laboratory calibrations, it is possible to establish expressions relating the soil apparent dielectric constant and the bulk electrical conductivity with the gravimetric water content and the dry density. Copyright ASCE 2007.

Morphotropic phase boundary and electrical properties of 1-x[Bi 0.5Na0.5]TiO3 -xBa[Zr0.25Ti 0.75]O3 lead-free piezoelectric ceramics

Lead-free solid solutions (1-x)Bi0.5Na0.5TiO 3 (BNT)-xBaZr0.25Ti0.75O3 (BZT) (x=0, 0.01, 0.03, 0.05, and 0.07) were prepared by the solid state reaction method. X-ray diffraction (XRD) and Rietveld refinement analyses of 1-x(BNT)-x(BZT) solid solution ceramic were employed to study the structure of these systems. A morphotropic phase boundary (MPB) between rhombohedral and cubic structures occured at the composition x=0.05. Raman spectroscopy exhibited a splitting of the (TO3) mode at x=0.05 and confirmed the presence of MPB region. Scanning electron microcopy (SEM) images showed a change in the grain shape with the increase of BZT into the BNT matrix lattice. The temperature dependent dielectric study showed a gradual increase in dielectric constant up to x=0.05 and then decrease with further increase in BZT content. Maximum coercive field, remanent polarization and high piezoelectric constant were observed at x=0.05. Both the structural and electrical properties show that the solid solution has an MPB around x=0.05. © 2012 Elsevier Ltd and Techna Group S.r.l.

Estudo das propriedades dielétricas e de bloqueio das monocamadas automontadas

Pós-graduação em Biotecnologia - IQ

Caracterização dielétrica de partículas nanométricas e nanoestruturadas de óxido de niobato da família tetragonal tungstênio bronze com estequiometria K'Sr IND. 2' N'b IND. 5' 'O IND. 15'

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)