Synthesis and luminescence properties of water dispersible Eu3+-doped boehmite nanoparticles

Nanocrystallized boehmite gamma-AlOOH center dot nH(2)O had been synthesized by spray-drying (SD) of a solution of aluminium tri-sec-butoxide peptized by nitric acid. The sub-micronic spherical particles obtained had an average diameter of 500 nm and were built of 100 nm or less platelet-like sub-particles. The average crystallite size calculated from XRD was 1.6 nm following the b axis (i.e. one unit cell) and 3-4 nm perpendicular to b. As a result of the nanometric sizes of crystallites, there was a large surface free for water adsorption and it was found to be n = 1.18 +/- 0.24H(2)O per AlOOH. The SD spheres spontaneously dispersed in water at room temperature and formed stable-over months-suspensions with nanometre-size particles (25-85 nm). Luminescent europium-doped nanocrystallized boehmites AlOOH: Eu (Al0.98Eu0.02OOH center dot nH(2)O) were synthesized the same way by SD and demonstrated the same crystallization properties and morphologies as the undoped powders. It is inferred from the Eu3+ luminescence spectroscopy that partly hydrated europium species are immobilized on the boehmite nanocrystals where they are directly bonded to alpha(OH) groups of the AlOOH surface. The europium coordination is schematically written [Eu3+(OH)(alpha)(H2O)(7-alpha/2)]. The europium-doped boehmite from SD spontaneously dispersed in water: the luminescence spectroscopy proves that most of the Eu3+ ions were detached from the NPs during water dispersion. The AlOOH: Eu nanoparticles were modified by the amine acid asparagine (ASN). The modification aimed to render the NPs compatible for further bio-functionalization. After surface modification, the NPs easily dispersed in water; the luminescence spectra after dispersion prove that the Eu3+ ions were held at the boehmite surface.

Effects of crystallization conditions on dielectric and ferroelectric properties of PZT thin films

This paper reports studies on dielectric and ferroelectric properties of lead zirconate titanate (PZT) thin films crystallized by conventional thermal annealing (CTA) and rapid thermal annealing (RTA) in air, oxygen and nitrogen atmospheres to better understand, control and optimize these properties. The dielectric constant (epsilon) and dissipation factor (tan delta) values, at a frequency of 100 kHz; for film crystallized in air by CTA process, were 358 and 0.039, respectively. Considering the same frequency for film crystallized in air by RTA, these values were 611 and 0.026, respectively. The different dielectric values were justified by a space-charge or interfacial polarization in films, often characterized as Maxwell-Wagner type. This effect was also responsible to dispersion at frequencies above 1 MHz in film crystallized in air by CTA process and film crystallized by RTA in oxygen atmosphere. The film crystallized by RTA under nitrogen atmosphere presented an evident dispersion at frequencies around 100 Hz, characterized by an increase in both epsilon and tan delta. This dispersion was attributed to conductivity effects. The remanent polarization (P-r) and coercive field (E-c) were also obtained for all films. Films obtained from RTA in air presented higher P-r (17.8 muC cm(-2)) than film crystallized from CTA (7.8 muC cm(-2)). As a function of the crystallization atmospheres, films crystallized by RTA in air and nitrogen presented essentially the same P-r values (around 18 muC cm(-2)) but the P-r (3.9 muC cm(-2)) obtained from film crystallized under oxygen atmosphere was profoundly influenced.

Crystallization kinetics and thermal properties of 20Li(2)O-80TeO(2) glass

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Crystallization and preliminary X-ray diffraction analysis of a Lys49-phospholipase A(2) complexed with caffeic acid, a molecule with inhibitory properties against snake venoms

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

Effect of partial crystallization on the mechanical properties and cytotoxicity of bioactive glass from the 3CaO center dot P2O5-SiO2-MgO system

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

Influence of thickness on crystallization and properties of LiNbO3 thin films

Thin films of lithium niobate were deposited on Pt/Ti/SiO2 (111) substrates by spin coating from the polymeric precursor method (Pechini process). Annealing in static air was performed at 500 degreesC for 3 h. The obtained films were characterized by X-ray diffraction and atomic force microscopy. The dielectric constant, dissipation factor and resistance were measured in frequency region from 10 Hz to 10 MHz and the hysteresis loop was obtained. The influence of number of layers on crystallization, morphology and properties of LiNbO3 thin films is discussed. (C) 2003 Elsevier B.V. All rights reserved.

Influence of oxygen atmosphere on crystallization and properties of LiNbO3 thin films

Thin films of lithium niobate were deposited on the Pt/Ti/SiO2 (111) substrates by spin coating from the polymeric precursor method (Pechini process). Annealing in static air and oxygen atmosphere was performed at 500 degreesC for 3 h. The films obtained were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The dielectric constant and dissipation factor were measured in frequency region from 10 Hz to 10 MHz. Electrical characterization of the films pointed to ferroelectricity via hysteresis loop. The influence of oxygen atmosphere on crystallization, morphology and properties of LiNbO3 thin films is discussed. (C) 2003 Elsevier Ltd. All rights reserved.

The influence of crystallization route on the properties of lanthanum-doped Bi4Ti3O12 thin films prepared from polymeric precursors

Pure and lanthanum-doped Bi4Ti3O12 thin films were deposited on Pt/Ti/SiO2/Si substrate using a polymeric precursor solution. The spin-coated films were specular and crack-free and crystalline after annealing at 700 degreesC for 2 h. Crystallinity and morphological evaluation were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Multilayered films obtained using the intermediate-crystalline layer route present a dense microstructure with spherical grains. Films obtained using the intermediate-amorphous layer, present elongated grains around 250 nm in size. The dielectric and ferroelectric properties of the lanthanum-doped Bi4Ti3O12 films are strongly affected by the crystallization route. The hysteresis loops are fully saturated with a remnant polarization and drive voltage of the films, heat-treated by the intermediate-crystalline (P-r = 20.2 muC/cm(2) and V = 1.35 V) and for the film heat-treated by amorphous route (P-r = 22.4 muC/cm(2) and V = 2.99 V). (C) 2004 Elsevier B.V. All rights reserved.

Effect of low contents of a polyaniline derivative on the crystallization and electrical properties of blends with PVDF

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

Crystallization mechanism and properties of a blast furnace slag glass

The complex crystallization process of a Brazilian blast-furnace slag glass was investigated using differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy, transmission electron microscopy (TEM), selected area diffraction (SAD), energy dispersive spectroscopy (EDS) and micro-Raman spectroscopy. Three crystalline phases (merwinite, melilite and larnite) were identified after heat treatment between Tg (742°C) and the DSC crystallization peak (T = 1000°C). Merwinite was identified as a metastable phase. A small amount (0.004 wt%) of metallic platinum was found in the glass composition. Particles of Pt3Fe, detected by EDS and SAD-TEM, were the starting points of crystallization acting, therefore, as heterogeneous nucleating sites. Only melilite and larnite precipitated in a glass sample heat-treated at 1000°C for 1 h. The flexural strength of this crystallized sample was less than that of the glass, probably due the allotropic phase transformation of larnite. © 2000 Published by Elsevier Science B.V. All rights reserved.

Crystallization and optical properties of CCTO thin films under pressure influence

CCTO thin films were deposited on Pt(111)/Ti/SiO 2/Si substrates using a chemical (polymeric precursor) and pressure method. The pressure effects on the CCTO thin films were evaluated by XRD, FEG-SEM and optical properties. Pressure films were found to be more homogeneous and dense than chemical deposition films. Pressure also leaded to an increase in the photoluminescence emission; it is suggested that the displacement of Ti in the titanate clusters, favors the charge transference from TiO 6 to [TiO 5V o z], TiO 5V o z] to [CaO 11V o z] and [TiO 5V o z] to [CuO 4] x. The low synthesis temperature used in the pressure method allows the deposition of films on less expensive substrates (i.e. glass, aluminum, polymer and others).

Properties of glass-ceramics obtained from crystallization of the SiO2-Al2O3-MgO-Li2O system with addition of ZrO2

This paper presents the study results with glass-ceramics obtained from base glass (MgO-Al2O3- SiO2-Li2O system) with addition of ZrO2 as nucleating agent. The glass was melted at 1650 degrees C for 3 h and at a heating rate of 10 degrees C/min. The molten glass was poured into a graphite mold to obtain monolithic samples and also in water in order to obtain particulate material. Such material was grinded and then pressed by both uniaxial and isostatic pressing methods before being sintered. Both the monolithic and pressed samples were performed under two different conditions of heat treatment so that their nucleation and crystallization occurred. In the first one, the samples were heated to 1100 degrees C with a heating rate of 10 degrees C/min. In the second one, there was an initial heating rate of 10 degrees C/min up to 780 degrees C, which was kept for 5 minutes. After that, the samples were heated to 1100 degrees C at a heating rate of 1 degrees C/min. Microhardness analyses showed that base glass presented values around 7.0 GPa. The glass-ceramics obtained from the powder sintering showed microhardness values lower than those obtained from monolithic samples. The highest hardness values were observed in the samples which were treated with two heating rates, whose values were around 9.2 +/- 0.5 GPa. Moreover, the glass-ceramics which were produced with an only heating rate, presented values around 7.1 +/- 0.2 GPa, very close to those observed in the base glass.

Crystallization, preliminary X-ray analysis and molecular-replacement solution of haemoglobin-II from the fish matrinxa (Brycon cephalus)

Haemoglobins constitute a set of proteins with interesting structural and functional properties, especially when the two large animal groups reptiles and fishes are focused on. Here, the crystallization and preliminary X-ray analysis of haemoglobin-II from the South American fish matrinxa (Brycon cephalus) is reported. X-ray diffraction data have been collected to 3.0 Angstrom resolution using synchrotron radiation (LNLS). Crystals were determined to belong to space group P2(1) and preliminary structural analysis revealed the presence of two tetramers in the asymmetric unit. The structure was determined using the standard molecular-replacement technique.

Structural and electrochemical properties of LiCoO2 prepared by combustion synthesis

LiCoO2 powders were prepared by combustion synthesis, using metallic nitrates as the oxidant and metal sources and urea as fuel. A small amount of the LiCoO2 phase was obtained directly from the combustion reaction, however, a heat treatment was necessary for the phase crystallization. The heat treatment was performed at the temperature range from 400 up to 700 degreesC for 12 h. The powders were characterized by X-ray diffraction (XRD), X ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and specific surface area values were obtained by BET isotherms. Composite electrodes were prepared using a mixture of LiCoO2, carbon black and poly(vinylidene fluoride) (PVDF) in the 85:10:5% w/w ratio. The electrochemical behavior of these composites was evaluated in ethylene carbonate/dimethylcarbonate solution, using lithium perchlorate as supporting electrolyte. Cyclic voltammograms showed one reversible redox process at 4.0/3.85 V and one irreversible redox process at 3.3 V for the LiCoO2 obtained after a post-heat treatment at 400 and 500 degreesC.Raman spectroscopy showed the possible presence of LiCoO2 with cubic structure for the material obtained at 400 and 500 degreesC. This result is in agreement with X-ray data with structural refinement for the LiCoO2 powders obtained at different temperatures using the Rietveld method. Data from this method showed the coexistence of cubic LiCoO2 (spinel) and rhombohedral (layered) structures when LiCoO2 was obtained at lower temperatures (400 and 500 degreesC). The single rhombohedral structure for LiCoO2 was obtained after post-heat treatment at 600 degreesC. The maximum energy capacity in the first discharge was 136 mA g(-1) for the composite electrode based on LiCoO2 obtained after heat treatment at 700 degreesC. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Crystallization study of the (1-x)Sb2O3-(x)SbPO4 glass system

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)