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Ronaldo Santos da Silva Maria Inês Basso Bernardi Antonio Carlos Hernandes 《Journal of Sol-Gel Science and Technology》2007,42(2):173-179
In this work, we have studied the influence of the pH on the synthesis and structural properties of the Ba0.77Ca0.23TiO3 nanopowders synthesized by a modified polymeric precursor method, in order to achieve non-agglomerated powders. Synthesis,
morphology, thermal reactions, crystallite and average particle size of the synthesized powders were investigated through
thermal analysis (DTA/TG), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and Infrared spectroscopy.
In summary, Ba0.77Ca0.23TiO3 nanopowders were synthesized for the first time at a relative low temperature (500 °C). It was also found that the alkalinity
and acidity of the solution presented a great influence on the powder properties. The best results were obtained from solutions
with pH = 8.5 and 11 whose nanopowders presented weakly agglomerate, with homogeneous particle size and a narrow size distribution
(30–40 nm). This behavior could be explained based on the FT-IR results in which it was possible to see the increased of the
chelation in higher pHs. 相似文献
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Maíra A. Carvalho Joo Bosco P. Da Silva Marcelo Z. Hernandes 《International journal of quantum chemistry》2005,102(4):379-386
The molecular electrostatic potential (MEP) of the indole molecule was calculated in a three‐dimensional grid in which the molecule was centered at the origin. To evaluate the dependence of MEP on the type of calculation, semiempirical, ab initio, and density functional theory methods with different basis sets were employed. The data matrix generated by these calculations was analyzed by principal component analysis (PCA). The appearance of outliers and the effect of wavefunction modifications such as the introduction of electron correlations and diffuse functions were highlighted by the use of PCA. The spatial localization of such effects around the molecule was possible from the loadings values associated with the graphical analysis of the grid points. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
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Lauro J.Q. Maia Valmor R. Mastelaro Antonio C. Hernandes 《Journal of solid state chemistry》2007,180(2):611-618
A new sol-gel route was applied to obtain Y0.9Er0.1Al3(BO3)4 crystalline powders and amorphous thin films by using Al(acac)3, B(OPri)3, Y(NO3)3·6H2O, and Er(NO3)3·5H2O as starting materials dissolved in propionic acid and ethyl alcohol mixtures. Our study shows that propionic acid acts as good chelant agent for yttrium and erbium ions while ethyl alcohol allows to dissolve Al(acac)3. This process makes the resulting sols very stable to obtain homogeneous gels and transparent amorphous thin films. In addition, the propionic acid prevents the sol precipitation, making easy porous- and crack-free thin film depositions. Chemical reactions involved in the complexation were discussed. As-prepared powders and films are amorphous and present a good thermal stability due to their high glass transition (746 °C) and crystallization temperatures (830 °C). This new sol-gel route showed to be adequate to obtain dense and crack-free thin films free of organic and hydroxyl groups that can be considered as promising materials to be used in integrated optical systems. 相似文献
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J.J.?RomeroEmail author M.R.B.?Andreeta E.R.M.?Andreeta L.E.?Bausá A.C.?Hernandes J.?García Solé 《Applied Physics A: Materials Science & Processing》2004,78(7):1037-1042
The growth from ceramic pedestals of single crystal fibers of strontium barium niobate (SBN), doped with different Nd concentrations, was studied. High-quality fibers were grown for Nd doping levels of up to 4.2 at.%, and doping levels as high as 9.9 at.% were reached. No signs of core effects were observed, even for the highest concentration samples. The emission spectra of Nd3+ ions in the fibers did not differ from those obtained from bulk SBN crystals, showing very broad bands due to the typical disorder of the crystallographic tungsten-bronze structure. Fluorescence quenching was clearly observed for Nd doping levels above 2 at.%. PACS 81.10.Fq; 78.55.-m 相似文献
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In this work we analyze the case of resistive conductor plates carrying constant currents, utilizing surface charge distributions. We obtain the electric potential in the plates and in the space surrounding them. We obtain a non-vanishing electric field outside the conductors. We compare the theoretical results with experimental data present in the literature. 相似文献
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S. S. Rojas G. J. M. Frigo M. I. B. Bernardi A. N. de S. Rastelli A. C. Hernandes V. S. Bagnato 《Journal of Thermal Analysis and Calorimetry》2010,99(1):263-268
We have investigated the thermal and structural properties of different commercial dental resins: FiltekTM Z-350, Grandio®, Tetric Ceram®, and TPH Spectrum®. The purpose of the present study was to evaluate quantitatively the photo-polymerization behavior and the effect of filler contents on the kinetic cures of the dental resins by using Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FT-IR) techniques. We have successfully obtained the low and high glass transition T g values of the dental composite resins from DSC curves. It was also observed a good agreement between the both T g values, activation energies from thermal degradation, and the degree of conversion obtained for all samples. The results have shown that Tetric Ceram® dental resin presented the higher T g values, activation energy of 215 ± 6 KJ mol?1, and the higher degree of conversion (63%) when compared to the other resins studied herein. 相似文献
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The weighted oscillator strengths gf and the lifetimes for S XIV presented in this work have been calculated in a multiconfigurational Hartree–Fock relativistic
approach. In this calculation, the electrostatic parameters were optimized by a least-squares procedure in order to improve
the adjustment to experimental energy levels. This method produces gf values that are in better agreement with observed line intensities and lifetime values closer to the experimentally determined
ones. In this work we presented all the experimentally known electric dipole S XIV spectral lines.
Published in Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 473–476, 2009. 相似文献
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