Thermostimulated sol-gel transition in suspensions of sulfate zirconium oxychloride

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Theoretical and experimental study of the relation between photoluminescence and structural disorder in barium and strontium titanate thin films

Thin films of barium and strontium titanate (BST), synthesized by the polymeric precursor solution and spin coated on [Pt (140nm)/Ti (10 nM)/SiO2(1000 nm)/Si] substrates were found to be photoluminescent at room temperature when heat treated below 973 K, i.e. before their crystallization. First principles quantum mechanical techniques, based on density functional theory (DFT) were employed to study the electronic structure of two periodic models: one is standing for the crystalline BST thin film and the other one for the structurally disordered thin film. The aim is to compare the photoluminescence (PL) spectra of the crystalline and disordered thin films with their UV-vis spectra and with their computed electronic structures. The calculations show that new localized states are created inside the band gap of the crystalline model, as predicted by the UV-vis spectra. The study of the charge repartition in the structure before and after deformation of the periodic model shows that a charge gradient appears among the titanate clusters. This charge gradient, together with the new localized levels, gives favorable conditions for the trapping of holes and electrons in the structure, and thus to a radiative recombination process. Our models are not only consistent with the experimental data, they also allow to explain the relations between structural disorder and photoluminescence at room temperature. (c) 2005 Elsevier Ltd. All rights reserved.

Ferroelectric properties of mechanically synthesized nanosized barium titanate

Barium titanate ceramics were prepared through mechanochemical synthesis starting from fresh prepared barium oxide and titanium oxide in rutile form. Mixture of oxides was milled in zirconia oxide jar in the planetary ball-mill during 30, 60, 120 and 240 min. Extended time of milling directed to formation of higher amount of barium titanate perovskite phase. Barium titanate with good crystallinity was formed after 240 min. Sintering without pre-calcinations step was performed at 1330 degrees C for 2 hours with heating rate of 10 degrees C/min. The XRD, DSC, IR and TEM analyses were performed. Electric and ferroelectric properties were studied. Very well defined hysteresis loop was obtained.

Improvement of the chemical resistance of zirconium fluoride glasses coated with a Tiron (R) modified tin oxide layer prepared by the sol-gel process

In order to improve the chemical resistance of zirconium fluoride glass a protective transparent SnO2 layer was deposited by the solgel dip-coating process in the presence of Tiron (R) as particle surface modifier agent. After water immersion for different periods of time, both coated and non-coated fluoride glasses were analyzed by scanning electron microscopy, mass loss evaluation, infrared spectroscopy and X-ray photoelectron spectroscopy. In contrast to the effects occurring for non-coated glass, where the surface undergoes a rapid selective dissolution of the most soluble species, the results for the SnO2-coated glass showed that the filling of the film nanopores by dissolved glass material results in a hermetic barrier protecting the glass surface. The selective glass dissolution was confirmed by liquid chromatography measurements of the etching solution after each exposure time. (c) 2006 Elsevier B.V. All rights reserved.

Barium strontium titanate nanocrystalline thin films prepared by soft chemical method

Barium strontium titanate (Ba0.65Sr0.35TiO3) nanocrystalline thin films, which were produced by the soft chemical method, were crystallized at low temperature using a domestic microwave oven. A SiC susceptor were used to absorb the microwave energy and rapidly transfer the heat to the film. Low microwave power and short time have been used. The films obtained are crack-free, well-adhered, and fully crystallized. The microstructure displayed a polycrystalline nature with nanograin size. The metal-BST-metal structure of the thin films treated at 700 degrees C show food electric properties. The ferroelectric nature of the BST35 thin film was indicated by buttertly- shaped C-V curves. The capacitance-frequency curves reveal that the dielectric constant may reach a value up to 800 at 100kHz. The dissipation factor was 0.01 at 100kHz. The charge storage density as function of applied voltage graph showed that the charge storage densities are suitable for use in trench type 64 Mb ( 1-5 mu C/cm(2) and 265 Mb (2-11 mu C/cm(2)) DRAMs. (C) 2007 Elsevier Ltd. All rights reserved.

Barium titanate screen-printed thick films

Barium titanate (BT) thick films were prepared from mechanically activated powders based on BaCO(3) and TiO(2). After homogenization and milling in a high-energy vibro mill, the powders were calcined at 700 degreesC for 2 h by slow heating and cooling rates. A thick film paste was prepared by mixing BT fine powders with small amount of low temperature sintering aid and organic binder. The thick films were screen-printed on alumina substrates electroded with Ag-Pd. The BT films were sintered at 850 degreesC for 1 h. The thickness was 25-75 mum depending of number of layers. The microstructure of thick films and the compatibility between BT layers and substrate were investigated by SEM Results of dielectric property measurements are also reported. (C) 2002 Elsevier B.V. Ltd and Techna S.r.l. All rights reserved.

Strontium titanate films prepared by spray pyrolysis

Strontium titanate thin films were prepared by spray pyrolysis technique. Deposition parameters, such as solution concentration, time and temperature of deposition, and flow rate of carrier gas were optimized to obtain dense films without cracks. Films with different thicknesses were prepared through the control of deposition time. Prepared thin films were homogeneous, well crystallized, with uniform grain size. (C) 2003 Elsevier Ltd. All rights reserved.

Effect of additives and powder preparation techniques on PTCR properties of barium titanate

PTCR barium titanate has been prepared following two different powder preparation techniques: the solid-state reaction route and co-precipitation route for the comparison of results. The co-precipitation route produces better PTCR characteristics with low room temperature resistivity and better reproducibility of prepared samples. The effects of different concentrations of additives like donors, acceptors and excess titanium have been optimized to get good quality PTCR samples. (C) 2002 Elsevier B.V. B.V. All rights reserved.

In vitro biocompatibility of poly(vinylidene fluoride-trifluoroethylene)/barium titanate composite using cultures of human periodontal ligament fibroblasts and keratinocytes

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

Influence of temperature on the dielectric and ferroelectric properties of bismuth titanate thin films obtained by the polymeric precursor method

The (1 1 7) and (0 0 1 0)-oriented Bi4Ti3O12 thin films were fabricated on Pt/Ti/SiO2/Si substrates by using a polymeric precursor solution under appropriate crystallization conditions. Atomic force microscopy and scanning electron microscopy showed relatively large grains, which is typical for this system. The capacitance dependence on voltage is strongly non-linear, confirming the ferroelectric properties of the films resulting from the domain switching. The (1 1 7)-oriented films exhibited a higher remanent polarization (23.7 μ C cm(-2)) than the (0 0 1 0)-oriented films (11.8 μ C cm(-2)). Fatigue tests revealed that the temperature of thermal treatment and degree of orientation affect the performance of the device. © 2005 Elsevier B.V. All rights reserved.

An insight into the theoretical investigation of possible piezoelectric effect in samarium titanate (SmTiO3)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Electrical Properties of Textured Niobium-Doped Bismuth Titanate Ceramics

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

Stimuli-responsive controlled growth of mono- and bidimensional particles from basic zirconium sulfate hydrosols

A thermostimulated sol-gel transition in a system prepared by mixing a ZrOCl(2) acidified solution to a hot H(2)SO(4) aqueous solution was studied by dynamic theological measurements and quasi-elastic light scattering. The effect of temperature and of molar ratio R(S) = [Zr]/[SO(4)] on the gelation kinetics was analyzed using the mass fractal aggregate growth model. This study shows that the linear growth of aggregates occurs at the early period of transformation, while bidimensional growth occurs at the advanced stage. The bidimensional growth can be shifted toward monodimensional growth by decreasing the aggregation rate by controlling the temperature and/or molar ratio R(S). EXAFS and Raman results gave evidence that the linear chain growth is supported by covalent sulfate bonding between primary building blocks. At the advanced stage of aggregation, the assembly of linear chains through hydrogen bonding gave rise to the growth of bidimensional particles.

Photopatternable di-ureasil-zirconium oxocluster organic-inorganic hybrids as cost effective integrated optical substrates

Organic-inorganic hybrids containing methacrylic acid (McOH, CH(2)= C(CH(3))COOH)) modified zirconium tetrapropoxide, Zr(OPr(n))(4), classed as di-ureasil-zirconium oxo-cluster hybrids, have been prepared and structurally characterized by X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), Fourier transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies, Si and C nuclear magnetic resonance (NMR), and atomic force microscopy (AFM). XRD and SAXS results have pointed out the presence of Si- and Zr-based nanobuilding blocks (NBBs) dispersed into the organic phase. Inter-NBBs correlation distances have been estimated for the pure di-ureasil and a model compound obtained. by hydrolysis/condensation of Zr(OPr(n))(4):McOH (molar ratio 1: 1): d(Si) approximate to 26 +/- 1 angstrom and d(Zr) approximate to 16 +/- 1 angstrom, respectively. In the case of the di-ureasil-zirconium oxo-cluster hybrids, these distances depend on the Zr relative molar percentage (rel. mol. Zr %) (d(Si) ranges from 18 to 25 angstrom and d(Zr) from 14 to 23 angstrom, as the rel. mol. Zr % increases from 5 to 75), suggesting that the Si- and Zr-based clusters are interconstrained. Complementary data from FT-IR, FT-Raman, (29)Si and (13)C NMR, and AFM support to a structural model where McOH-modified Zr-based NBBs (Zr-OMc) are present over the whole range of composition. At low Zr-OMc contents (rel. mol. Zr % <30) the clusters are well-dispersed within the di-ureasil host, whereas segregation occurs at the 0.1 mu m scale at high Zr-OMc concentration (rel. mol. Zr % = 50). No Zr-O-Si heterocondensation has been discerned. Monomode waveguides, diffractions gratings, and Fabry-Perot cavities have been written through the exposure of the hybrid monoliths to UV light. FT-Raman has shown that the chemical process that takes place under illumination is the polymerization of the methacrylate groups of the Zr-OMc NBBs. The guidance region in patterned channels is a Gaussian section located below the exposed surface with typical dimensions of 320 mu m wide and 88 mu m deep. The effective refractive index is 1.5162 (maximum index contrast on the order of 1 x 10(-4)) and the reflection coeficient of the Fabry-Perot cavity (formed by a grating patterned into a 0.278 cm channel) is 0.042 with a free spectral range value of 35.6 GHz.

Enhanced photoluminescence features of Eu3+-modified di-ureasil-zirconium oxocluster organic-inorganic hybrids

In this work, a series of transparent di-ureasil hybrids containing different amounts of methacrylic acid modified zirconium tetrapropoxide (ZrMcOH) nanoclusters (5-85 mol%) and incorporating EuCl3 and [Eu(tta)(3)(H2O)(2)](tta = thenoyltrifluoroacetonate) complex were prepared. These hybrids are multi-wave-length emitters due to the convolution of the host intrinsic emission (electron-hole recombinations occurring in siliceous and urea cross-linkages) Eu3+ intra-4f(6) transitions. The ZrMcOH incorporation deviates the maximum excitation wavelength of the hybrid host intrinsic emission from the UV (365 nm) to the blue (420 nm) and enhances the absolute emission quantum yield from 6.0 +/- 0.6% to 9.0 +/- 0.9%, and contributes to an increase in the D-5(0) lifetime values, quantum efficiency due to a decrease in the non-radiative transition probability and OH groups coordinated to the Eu3+ ions. (C) 2010 Elsevier B.V. All rights reserved.