Caracterização elétrica e microestrutural de cerâmicas varistoras de baixa tensão à base de ('SN IND.1-x''TI IND.x')'O IND.2' e 'SN''O IND.2' dopados com 'CO''O' e 'NB IND.2''O IND.5'

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo de um sistema varistor à base de 'SN''O IND.2' dopado com terras-raras

Pós-graduação em Química - IQ

Preparação e caracterização de filmes finos de 'BA''BI IND.2''TA IND.2''O IND.9(BBT)' e 'BA''BI IND.2''NB IND.2''O IND.9(BBN)'

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

CoO doping effects on the ZnO films through EBPDV technique

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

Investigação da condução elétrica em fitas duplas de dna imobilizadas em eletrodos de ouro por medidas eletroquímicas

Pós-graduação em Química - IQ

Adsorption of pH-responsive polyelectrolyte chains onto spherical macroions

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Otimização do processamento de partículas lead-free para aplicação em compósitos polímero/cerâmica com propriedades piezoelétrica e fotoluminescente

Pós-graduação em Química - IQ

Monofilamentary Ag/Bi:2212 tapes - Effects of silver powder addition

The Bi-Sr-Ca-Cu-O system has been one of the most studied superconducting ceramic materials for industry applications. The most of the studies with this aim are on silver/ceramic composites, due to the benefits and great compatibility of this metal with the oxide. Tapes made by the powder in tube (PIT) method have been successfully tested in pilot power plants in many countries but in Brazil. In this paper, 5, 10, and 20-wt% silver powders are introduced to compose the core of the tape along with the Bi:2212 ceramic powder. The results of electrical experiments are compared with those made with no silver addition Ag tapes. The best current density, at 60 K and no applied magnetic field, was found for the 10-wt% silver proportion, doubling the value obtained for the tape with no silver in the core.

Structural and Electric-Optical Properties of Zinc Phthalocyanine Evaporated Thin Films: Temperature and Thickness Effects

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

Dynamical properties for the problem of a particle in an electric field of wave packet: Low velocity and relativistic approach

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

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.

Electric and magnetic properties of polymer electrolyte/carbon black composites

Measurements of 1H Nuclear Magnetic Resonance (NMR) relaxation times, Electron Paramagnetic Resonance (EPR) and AC Impedance Spectroscopy (IS) are reported for composites based on PEO8:LiClO4 and carbon black (CB), prepared by two methods: solvent and fusion processing. Three nuclear relaxation processes were identified for 1H nuclei: (i) belonging to the polymer chains in the amorphous phase, loosely bound to the CB particles, whose dynamics is almost the same as for unfilled polymer, (ii) belonging to the polymer chains which are tightly attached to the CB particles, and (iii) belonging to the crystalline phase in the loose polymer chain. The paramagnetic electronic susceptibility of the composite samples, measured by EPR, was interpreted by assuming a contribution of localized spin states that follow a Curie law, and a Pauli-like contribution of delocalized spins. A significant change of the EPR linewidth was observed at 40 K, which is the temperature where the Curie and Pauli susceptibilities equally contribute to the paramagnetic electronic susceptibility. The electrical properties are very sensitive to the preparation methods of the composites, which conditions the interaction between carbon particle-carbon particle and carbon particle-polymer chain. Classical statistic models to describe the conductivity in these media were not satisfactory. © 1998 Published by Elsevier Science B.V. All rights reserved.

Growth of Al2O3 thin film by oxidation of resistively evaporated Al on top of SnO2, and electrical properties of the heterojunction SnO2/Al2O3

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of Heat Treatment on the Anelastic Properties of MgB(2)

The discovery of the superconductivity of MgB(2) was of great importance, because this material is one of the few known binary compounds and has one of the highest critical temperatures (39 degrees K). As MgB(2) is a granular compound, it is fundamentally important to understand the mechanisms of the interaction of the defects and the crystalline lattice, in addition to the eventual processes involving the grain boundaries that compose the material. In this sense, the mechanical spectroscopy measurements constitute a powerful tool for this study, because through them we can obtain important information about phase transitions, the behavior of interstitial or substitutional elements, dislocations, grain boundaries, diffusion, instabilities, and other imperfections of the lattice. For this paper, the samples were prepared using the PIT method and were characterized by density, X-ray diffraction, scanning electron microscopy, electric resistivity, magnetization, and mechanical spectroscopy. The samples were measured in their as-cast condition and after an ultra-high-vacuum heat treatment. The results showed complex spectra, in which were identified relaxation processes due to dislocation movement, interaction among interstitial elements and dislocations, auto-diffusion, and movement of grain boundaries. Some of these processes disappeared with the heat treatment.