Growth and characterization of BaBi2Nb2O9 thin films made by RF-magnetron sputtering

The RF-magnetron sputtering technique has been used to deposit polycrystalline thin films of layered-structured ferroelectric BaBi2Nb2O9 (BBN). The XRD patterns for the films annealed at 700degreesC for 1 hour show the presence of the BBN phase as well as the BaNb2O6 secondary phase. A better crystallization of the BBN phase and an inhibition of the secondary phase is obtained with the increase of temperature. The surface of the prepared films was rather dense and smooth with no cracks. The 300 nm thick BBN thin films exhibited a room-temperature dielectric constant of about 779 with a dissipation factor of 0.09 at a frequency of 100 kHz.

Development of Ti-Mo alloys for biomedical applications: Microstructure and electrochemical characterization

Ti-Mo alloys from 4 to 20 Mo wt.% were arc-melted. Their compositions and surfaces were analyzed by EDX, XRF and SEM. The Mo mapping shows a homogeneous distribution for all alloys. The XRD analysis showed that the crystal structure of the alloys is sensitive to the Mo concentration; a mixture of the hexagonal alpha' and orthorhombic alpha '' phases was observed for the Ti-4Mo alloy, and the alpha '' phase is observed almost exclusively when the concentration of Mo added to the Ti reaches 6%. A significant retention of the beta phase is observed for the alloy containing 10% Mo, while at higher Mo concentrations (15% and 20%), retention of phase beta is only verified. Preliminary electrochemical studies have indicated a valve-metal behavior and good corrosion resistance in aerated Ringer solution for all alloys. (c) 2006 Published by Elsevier B.V.

Microstructural and morphological analysis of pure and Ce-doped tin dioxide nanoparticles

Structural morphological studies in pure and Ce-doped tin dioxide nanoparticles with high stability against particle growth were performed in samples, obtained using the polymeric precursor method and prepared at different annealing temperatures. A Ce-rich surface layer was used to control the particle size and stabilize SnO2 against particle growth. The formation of this segregated layer can contribute to a decreased surface energy, acting in the driving force, or reducing the surface mobility. Only the cassiterite SnO2 phase was observed below 1000 degreesC and a secondary phase (CeO2) was observed for the Ce-doped SnO2 at temperatures higher than 1000 degreesC, when de-mixing process occurs. The evolution of crystallite size, microstrain and morphology of the nanoparticles with annealing temperatures was investigated by X-ray diffraction (XRD), associated to Rietveld refinements, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). (C) 2002 Elsevier B.V. Ltd. All rights reserved.

New X-ray powder diffraction data and Rietveld refinement for Gd2O3 monodispersed fine spherical particles

Nominally pure Gd2O3 C-form structure from basic carbonate fine spherical particles and its differences concerning the XRD data among literature patterns using Rietveld method is reported. Gd2O3: Eu3+ from basic carbonate and Gd2O3 from oxalate were also investigated. All samples, except the one from oxalate precursor, are narrow sized, 100-200 nm. Only non-doped Gd2O3 from basic carbonate presents XRD data with smaller d(hkl) values than the literature ones. From Rietveld refinement, non-doped Gd2O3 from basic carbonate has the smallest crystallite size and from oxalate shows the greatest one. Also, the unit cell parameters indicate a plan contraction of the Gd2O3 from basic carbonate. The presence of Eu3+ increases crystallite size when basic carbonate precursor is used to prepare Gd2O3 and avoids plan contraction. The structural differences observed among Gd2O3 samples obtained are related to the type of precursor and to the presence or not of doping ion. (C) 2003 Elsevier B.V. (USA). All rights reserved.

Preparation and characterization of nanosized SrBi2Nb2O9 powder by the combustion synthesis

This work presents the preparation of SrBi2Nb2O9 (SBN) directly by the combustion synthesis. Strontium nitrate, niobium ammonium oxalate (NH4H2[NbO-(C2O4)(3)].3H(2)O) and bismuth oxide were used as oxidant reactants and urea as fuel. The influence of the fuel was evaluated by the addition of different fuel amounts (50%, 100%, 200% and 300%), 100% being the stoichiometric proportion. The XRD patterns showed that the SBN perovskite crystallized as the majority phase. The as-synthesized stoichiometric powder presented a specific surface area of around 13 m(2)/g and a mean grain size of around 16 nm. Dilatometric measurements showed that the maximum sintering rate occurs at 1275degreesC. The determination of the ferroparaelectric transition showed a Curie temperature (T-c) of 429degreesC. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Microstructural and optical characterization of CaWO4 and SrWO4 thin films prepared by a chemical solution method

Stoichiometric CaWO4 and SrWO4 thin films were synthesized using a chemical solution processing, the so-called polymeric precursor method. In this soft chemical method, soluble precursors such as strontium carbonate, calcium carbonate and tungstic acid, as starting materials, were mixed in an aqueous solution. The thin films were deposited on glass substrates by means of the spinning technique. The surface morphology and crystal structure of the thin films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Nucleation stages and surface morphology evolution of the thin films on glass substrates were studied by atomic force microscopy. The films nucleate at 300 degreesC, after the coalescence of small nuclei into larger grains yielding a homogeneous dense surface. XRD characterization of these films showed that the CaWO4 and SrWO4 phases crystallize at 400 degreesC from an inorganic amorphous phase. No intermediate crystalline phase was identified. The optical properties were also studied. It was found that CaWO4 and SrWO4 thin films have an optical band gap, E-gap=5.27 and 5.78 eV, respectively, of a direct transition nature. The excellent microstructural quality and chemical homogeneity confirmed that this soft solution processing provides an inexpensive and environmentally friendly route for the preparation of CaWO4 and SrWO4 thin films. (C) 2003 Elsevier B.V. All rights reserved.

beta-ZnMoO4 microcrystals synthesized by the surfactant-assisted hydrothermal method: Growth process and photoluminescence properties

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

Structural Refinement and Photoluminescence Properties of MnWO4 Nanorods Obtained by Microwave-Hydrothermal Synthesis

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

Influence of simultaneous addition of MnO2 and CoO on properties of SnO2-based ceramics

This paper reports on a study of the: effect of replacing CoO by MnO2 on the sintering and electrical propel-ties of the 98.95% SnO2 + (1 - x)% CoO + x% MnO2 + 0.05% Ta2O5 system. All the samples were compacted into pellets and sintered at 1300 degrees C for 1 h, when they reached densities of about 98% of the theoretical density. An X-ray diffraction (XRD) analysis showed no other detectable phases other than SnO2. Current-voltage characterization indicated varistor behavior in the systems. The non-linear coefficient (alpha) and breakdown electric field (Eb) increased as the amount of MnO2 was increased. The results are explained in terms of an electric barrier modification, due to the presence of adsorbed negative oxygen species at the grain boundary inter face. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Synthesis, growth process and photoluminescence properties of SrWO4 powders

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Synthesis, structural refinement and optical behavior of CaTiO3 powders: A comparative study of processing in different furnaces

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A comparative study of the electrogeneration of hydrogen peroxide using Vulcan and Printex carbon supports

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Preparation of CuO/SiO2 and photocatalytic activity by degradation of methylene blue

A photocatalyst based on CuO/SiO2 was prepared, and evaluated for the degradation of methylene blue in aqueous medium. The photocatalyst was obtained by calcination method of copper salt, in the presence of silica. The characterization by XRD, FTIR, and TPR techniques confirmed the formation of CuO as active phase. SEM studies showed CuO deposited on the surface of SiO2. By ESI-MS, it was demonstrated that the degradation of methylene blue occurs through successive hydroxylations. Photodegradation assays showed that CuO/SiO2 was efficient for degradation, and that the material worked better in the presence of UV light.

Study of the annealing temperature effect on the structural and luminescent properties of SrWO4:Eu phosphors prepared by a non-hydrolytic sol-gel process

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

Structural refinement and photoluminescence properties of irregular cube-like (Ca-1_Cu-x(x))TiO3 microcrystals synthesized by the microwave-hydrothermal method

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)