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1.
Chemosphere ; 240: 124953, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31574435

RESUMO

Chemical characterization of PM2.5 and PM10 is important to identify potential compounds that induce biological responses that translate into cardio-respiratory health problems. This study shows the reliability of the use of crystalline phases, identified in samples from receptor sites, as source markers, helping researchers to infer the main sources of air pollution, even without the use of receptor models. PM2.5 and PM10 samples were collected at two sites in an urban industrialized region located at southeast of Brazil and analyzed by Synchrotron X-ray Diffraction to identify crystalline compounds. Results show 5 PM10 and PM2.5 species not previously reported in the literature. We propose reaction mechanisms for these species and identify specific sources for each crystalline phase found: BaTiO3 was found in PM10 receptor samples and proved to be a vehicular marker formed during brake action; maghemite (γ-Fe2O3), pyracmonite [(NH4)3Fe(SO4)3], ammonium perchlorate (NH3OHClO4) and potassium ferrate (K2Fe2O4) were found in PM2.5 proved to be markers of industrial activities. The crystalline phases found in PM samples from receptor sites and the mechanisms of reactions showed the reliability of the use of crystalline phases as source markers in the identification of potential sources of air pollution without misinterpretation of the likely source.


Assuntos
Poluentes Atmosféricos/análise , Poluição do Ar/análise , Monitoramento Ambiental/métodos , Material Particulado/análise , Material Particulado/química , Sulfato de Amônio/análise , Compostos de Bário/análise , Brasil , Compostos Férricos/análise , Indústrias , Compostos de Ferro/análise , Tamanho da Partícula , Percloratos/análise , Compostos de Potássio/análise , Compostos de Amônio Quaternário/análise , Reprodutibilidade dos Testes , Síncrotrons , Titânio/análise , Difração de Raios X/métodos
2.
Appl Spectrosc ; 71(3): 438-445, 2017 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-27645723

RESUMO

The infrared (IR) microspectroscopical analysis of samples within a sealed-cell containing barium fluoride is a critical need when identifying toxic agents or suspicious powders of unidentified composition. The dispersive nature of barium fluoride is well understood and experimental conditions can be easily adjusted during reflection-absorption measurements to account for differences in focus between the visible and IR regions of the spectrum. In most instances, the ability to collect a viable spectrum is possible when using the sealed cell regardless of whether visible or IR focus is optimized. However, when IR focus is optimized, it is possible to collect useful data from even smaller samples. This is important when a minimal sample is available for analysis or the desire to minimize risk of sample exposure is important. While the use of barium fluoride introduces dispersion effects that are unavoidable, it is possible to adjust instrument settings when collecting IR spectra in the reflection-absorption mode to compensate for dispersion and minimize impact on the quality of the sample spectrum.


Assuntos
Ciências Forenses/métodos , Microespectrofotometria/métodos , Pós/análise , Espectrofotometria Infravermelho/métodos , Compostos de Bário/análise , Terrorismo Químico/prevenção & controle , Fluoretos/análise , Pós/química
3.
Forensic Sci Int ; 269: 56-62, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-27866062

RESUMO

If police officers are contaminated with gunshot residue (GSR) through the normal receiving, checking, loading, and securing of their issued firearm, there is the potential for secondary transfer of GSR to anyone those officers arrest during their shift. This 3-part study examined the level of GSR contamination of police officers following the start-of-shift handling of their standard issue firearm, the impact that hand-washing or the use of a self-drying hand-wash had on the level of GSR contamination, and the likelihood of officers re-contaminating their hands through contact with the exposed hand-grip of their holstered hand-gun. Almost 85% (28/33) of officers sampled had 3-component GSR particles on their hands immediately following the start-of-shift handling of their firearm. There was an average of 64 such particles over the 33 officers sampled. Of the 17 officers who washed their hands after securing their firearm, a single 3-component particle was recovered from the hands of one officer. GSR particles (maximum of 4) were recovered from 3 of the 14 officers who used self-drying hand gel following firearm handling. 3-component particles (maximum of 7) were recovered from the hand-grips of 12 of the 34 unissued handguns sampled.


Assuntos
Antimônio/análise , Compostos de Bário/análise , Armas de Fogo , Mãos , Chumbo/análise , Polícia , Pele/química , Feminino , Luvas Protetoras , Desinfecção das Mãos , Humanos , Masculino , Nitratos/análise , Tato
4.
Nanomedicine (Lond) ; 10(13): 2051-61, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25953069

RESUMO

AIM: The in vivo study on imprinting control region mice aims to show that magnetoelectric nanoparticles may directly couple the intrinsic neural activity-induced electric fields with external magnetic fields. METHODS: Approximately 10 µg of CoFe2O4-BaTiO3 30-nm nanoparticles have been intravenously administrated through a tail vein and forced to cross the blood-brain barrier via a d.c. field gradient of 3000 Oe/cm. A surgically attached two-channel electroencephalography headmount has directly measured the modulation of intrinsic electric waveforms by an external a.c. 100-Oe magnetic field in a frequency range of 0-20 Hz. RESULTS: The modulated signal has reached the strength comparable to that due the regular neural activity. CONCLUSION: The study opens a pathway to use multifunctional nanoparticles to control intrinsic fields deep in the brain.


Assuntos
Compostos de Bário/química , Encéfalo/fisiologia , Cobalto/química , Eletroencefalografia/métodos , Compostos Férricos/química , Imãs/química , Nanopartículas/química , Titânio/química , Animais , Compostos de Bário/análise , Compostos de Bário/metabolismo , Barreira Hematoencefálica/fisiologia , Cobalto/análise , Cobalto/metabolismo , Campos Eletromagnéticos , Feminino , Compostos Férricos/análise , Compostos Férricos/metabolismo , Imãs/análise , Camundongos , Nanopartículas/administração & dosagem , Nanopartículas/análise , Nanopartículas/metabolismo , Nanopartículas/ultraestrutura , Titânio/análise , Titânio/metabolismo
5.
J Environ Health ; 76(6): 146-54, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24645426

RESUMO

The authors' aim was to explore whether geological factors contribute to geographical variation in the incidence of type 1 diabetes. All children diagnosed with type 1 diabetes in southeastern Sweden during 1977-2006 were defined geographically by their place of residence and were allocated x and y coordinates in the national grid. The population at risk, all children 0-16 years of age, was geocoded in a similar manner. Three of the analyzed minerals in moraine and one of the analyzed minerals in brook water plants were significantly associated with type 1 diabetes at the time of diagnosis. Additionally, the birthplace of the children who subsequently developed diabetes differed in relation to some of the minerals. In communities with high incidence and in communities with low incidence, children were diagnosed with type 1 diabetes in areas with the same high or low level of elements. The authors' findings in their pilot study indicate a possible geographical covariation of incidence and some geological factors.


Assuntos
Diabetes Mellitus Tipo 1/epidemiologia , Exposição Ambiental/análise , Abastecimento de Água/análise , Adolescente , Compostos de Bário/análise , Criança , Pré-Escolar , Mapeamento Geográfico , Humanos , Lactente , Modelos Logísticos , Metais Pesados/análise , Minerais/análise , Óxidos/análise , Suécia/epidemiologia
6.
Artigo em Inglês | MEDLINE | ID: mdl-23933549

RESUMO

Quantum Theory of Atoms in Molecules Charge-Charge Flux-Dipole Flux (QTAIM/CCFDF) models have been determined for the BF3 and BCl3 molecules. Model parameters were obtained from MP2/6-31G(2d,2p) wave functions owing to their accurate estimations of the BF3 intensities and were found to be insensitive to changes in basis sets with polarization functions and to the level of electron correlation treatment, MP2, QCISD and DFT. The BF3 stretching intensity has a very dominant equilibrium charge contribution with small charge and dipole fluxes occurring in the opposite direction to the charge movement. Large equilibrium charge and small dynamic contributions are also characteristic of stretching vibrations in the ionic diatomic molecules, NaF, NaCl, LiF and LiCl. Furthermore the Laplacians of the electron density at the bond critical points of BF3 and these diatomics are all positive indicating electron depletion in their bonding regions relative to large electronic densities concentrated around their nuclei that is characteristic of ionic bonds. The MP2/6-31G(2d,2p) BCl3 stretching intensity can be accurately estimated by equilibrium charge movement since the charge and dipole fluxes almost exactly cancel one another. Both in-plane and out-of-plane BF3 and BCl3 bending deformations are described by equilibrium charge movements that are partially canceled by opposing dipole fluxes that measure the effect on the dipole moment change from electron densities polarized in the opposite direction. Charge fluxes are calculated to be small for the in-plane deformations and are zero by symmetry for the out-of-plane ones.


Assuntos
Compostos de Bário/análise , Cloretos/análise , Fluoretos/análise , Elétrons , Teoria Quântica , Espectrofotometria Infravermelho
7.
ScientificWorldJournal ; 2013: 120983, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23844376

RESUMO

The dielectric nanosize dependence of BaTiO3 powders was investigated by the slurry method, where two series of BaTiO3 slurries with 10 vol% and 30 vol% solids loadings were prepared as model samples. Applying the Bruggeman-Hanai equation, the high-frequency limiting permittivity (ε(h)) of the slurries was extracted from the dielectric spectra. The ε(h) of the 10 vol% slurry showed abnormal size independence in the range from 100 nm to 700 nm, and the ε(h) of the 30 vol% slurry exhibited good agreement with the previous prediction. Through analysing quantitatively the response of ε(h) to the changing permittivity of the powders under different solids loading, it was found that the ε h of the slurry with lower solids loading is more inclined to be interfered by the systematic and random errors. Furthermore, a high permittivity value was found in the BaTiO3 powders with 50 nm particle size.


Assuntos
Compostos de Bário/análise , Compostos de Bário/síntese química , Nanopartículas/química , Nanopartículas/ultraestrutura , Titânio/análise , Impedância Elétrica , Teste de Materiais , Tamanho da Partícula , Pós
8.
Am J Forensic Med Pathol ; 34(2): 115-8, 2013 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-23629399

RESUMO

Barium is an alkaline earth metal which has a variety of uses including in the manufacturing industry and in medicine. However, adverse health effects and fatalities occur due to absorption of soluble barium compounds, notably the chloride, nitrate, and hydroxide, which are toxic to humans. Although rare, accidental and suicidal modes of poisoning are sporadically reported in the literature.We describe 4 cases of poisoning due to barium chloride in China. In witnessed cases, severe gastrointestinal symptoms, hypokalemia leading to muscle weakness, cardiac arrhythmias, and respiratory failure were noted. Autopsy showed some nonspecific but common findings, such as subendocardial hemorrhage in the ventricles, visceral petechiae, and fatty changes in the liver. Interestingly, microscopic examination showed degenerative changes and amorphous, flocculent foamy materials in the renal tubules. Toxicology was relevant for barium in blood and tissues. Three of the cases were accidental and 1 homicidal in nature. A round-up of relevant literature on fatal barium compounds poisoning is also provided. Forensic pathologists should be aware of the clinical presentations of barium compound poisoning and especially look for any evidence of hypokalemia. Still, postmortem toxicological and histological studies are essential for an accurate identification of the cause of death.


Assuntos
Compostos de Bário/envenenamento , Cloretos/envenenamento , Acidentes , Adulto , Arritmias Cardíacas/induzido quimicamente , Compostos de Bário/análise , Cloretos/análise , Diarreia/induzido quimicamente , Fígado Gorduroso/patologia , Patologia Legal , Toxicologia Forense , Ventrículos do Coração/patologia , Hemorragia/patologia , Homicídio , Humanos , Hipopotassemia/induzido quimicamente , Túbulos Renais/patologia , Masculino , Debilidade Muscular/induzido quimicamente , Miocárdio/patologia , Púrpura/patologia , Insuficiência Respiratória/induzido quimicamente , Vacúolos/patologia , Vômito/induzido quimicamente , Adulto Jovem
9.
J Synchrotron Radiat ; 20(Pt 3): 455-9, 2013 May.
Artigo em Inglês | MEDLINE | ID: mdl-23592625

RESUMO

To clarify the contrasting impurity effects of Mn and Zn dopants on the critical temperature of optimally doped Ba0.5K0.5Fe2As2 superconductors, extended X-ray absorption fine-structure spectroscopy was implemented at the Fe and As K-edge. In Mn-doped compounds a gradual deviation of the symmetric FeAs4 tetrahedron and weakening of the Fe-As bond was observed. Conversely, in Zn-doped compounds the perfect FeAs4 tetrahedron is maintained and the Fe-As bond is rigid. The local structural details are consistent with the development of superconductivity in these two systems, suggesting a significant role played by the topology of the FeAs4 tetrahedron and rigidness of the Fe-As bond in Mn/Zn-doped Ba0.5K0.5Fe2As2 superconductors.


Assuntos
Compostos de Bário/química , Manganês/química , Espectroscopia por Absorção de Raios X/métodos , Zinco/química , Compostos de Bário/análise , Condutividade Elétrica , Manganês/análise , Teste de Materiais , Conformação Molecular , Espalhamento de Radiação , Raios X , Zinco/análise
10.
Anal Chem ; 84(9): 4088-94, 2012 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-22468859

RESUMO

Particle size distribution and compactness have significant confounding effects on Raman signals of powder mixtures, which cannot be effectively modeled or corrected by traditional multivariate linear calibration methods such as partial least-squares (PLS), and therefore greatly deteriorate the predictive abilities of Raman calibration models for powder mixtures. The ability to obtain directly quantitative information from Raman signals of powder mixtures with varying particle size distribution and compactness is, therefore, of considerable interest. In this study, an advanced quantitative Raman calibration model was developed to explicitly account for the confounding effects of particle size distribution and compactness on Raman signals of powder mixtures. Under the theoretical guidance of the proposed Raman calibration model, an advanced dual calibration strategy was adopted to separate the Raman contributions caused by the changes in mass fractions of the constituents in powder mixtures from those induced by the variations in the physical properties of samples, and hence achieve accurate quantitative determination for powder mixture samples. The proposed Raman calibration model was applied to the quantitative analysis of backscatter Raman measurements of a proof-of-concept model system of powder mixtures consisting of barium nitrate and potassium chromate. The average relative prediction error of prediction obtained by the proposed Raman calibration model was less than one-third of the corresponding value of the best performing PLS model for mass fractions of barium nitrate in powder mixtures with variations in particle size distribution, as well as compactness.


Assuntos
Compostos de Bário/análise , Cromatos/análise , Compostos de Potássio/análise , Pós/química , Análise Espectral Raman/métodos , Algoritmos , Calibragem , Análise dos Mínimos Quadrados , Nitratos/análise , Tamanho da Partícula , Sensibilidade e Especificidade
11.
J Fish Biol ; 74(4): 891-905, 2009 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-20735606

RESUMO

This study examined the toxicological and physiological responses of a commercially important coral-reef grouper, Plectropomus leopardus (Serranidae), to injection of enriched stable-isotope barium chloride (BaCl(2)) solution. Thirty adult P. leopardus were subject to one of two (138)BaCl(2) injection treatment groups (corresponding to dosage rates of 2 and 4 mg (138)Ba kg(-1) body mass), and a control group in which fish were injected with 0.9% sodium chloride (NaCl) solution. Fish from each group were sampled at post-injection intervals of 48 h and 1, 3, 5 and 8 weeks, at which time blood and tissue samples were removed from each fish. Residual concentrations of Ba and (138)Ba:(137)Ba ratios were measured in muscle, gonad, liver and bone tissues of each experimental fish. Elevated Ba concentrations were detected in all treatment fish tissue samples within 48 h post injection. Residual Ba concentrations decreased throughout the remainder of the 8 week experimental period in all tissues except bone. The BaCl(2) injection had no significant effects on measured whole blood variables or on the plasma concentrations of steroid hormones. Enriched Ba stable isotopes can therefore be used at low dosages to mark larvae of commercially important marine fishes, without adverse effects on the health of the fishes or on humans who may consume them.


Assuntos
Sistemas de Identificação Animal/veterinária , Organismos Aquáticos/efeitos dos fármacos , Compostos de Bário/farmacologia , Bass/fisiologia , Cloretos/farmacologia , Marcação por Isótopo/veterinária , Animais , Compostos de Bário/análise , Compostos de Bário/sangue , Compostos de Bário/metabolismo , Compostos de Bário/toxicidade , Cloretos/análise , Cloretos/sangue , Cloretos/metabolismo , Cloretos/toxicidade , Feminino , Pesqueiros/métodos , Hormônios Esteroides Gonadais/sangue , Gônadas/efeitos dos fármacos , Indicadores e Reagentes/farmacologia , Indicadores e Reagentes/toxicidade , Masculino
12.
Artigo em Inglês | MEDLINE | ID: mdl-16859982

RESUMO

The principal component analysis (PCA) was applied to Raman spectra of polycrystalline BaTiO(3) under pressure from atmospheric pressure to approximately 6.72 GPa. For the system utilized, PCA was able to distinguish spectral features and to determine the phase transition pressure: tetragonal to cubic at approximately 2.0 GPa. The present study demonstrates the potentialities of the application of PCA to the investigation on phase transitions at high pressure by Raman spectroscopy.


Assuntos
Compostos de Bário/análise , Análise de Componente Principal/métodos , Análise Espectral Raman/métodos , Titânio/análise , Cristalização , Pressão
13.
Nano Lett ; 6(4): 735-9, 2006 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-16608274

RESUMO

We report scanned probe characterizations of the ferroelectric phase transition in individual barium titanate (BaTiO3) nanowires. Variable-temperature electrostatic force microscopy is used to manipulate, image, and evaluate the diameter-dependent stability of ferroelectric polarizations. These measurements show that the ferroelectric phase transition temperature (TC) is depressed as the nanowire diameter (dnw) decreases, following a 1/dnw scaling. The diameter at which TC falls below room temperature is determined to be approximately 3 nm, and extrapolation of the data indicates that nanowires with dnw as small as 0.8 nm can support ferroelectricity at lower temperatures. We also present density functional theory (DFT) calculations of bare and molecule-covered BaTiO3 surfaces. These calculations indicate that ferroelectricity in nanowires is stabilized by molecular adsorbates such as OH and carboxylates. These adsorbates are found to passivate polarization charge more effectively than metallic electrodes, explaining the observed stability of ferroelectricity in small-diameter BaTiO3 nanowires.


Assuntos
Compostos de Bário/química , Compostos de Bário/efeitos da radiação , Eletroquímica/métodos , Magnetismo , Nanotubos/química , Titânio/química , Titânio/efeitos da radiação , Anisotropia , Compostos de Bário/análise , Cristalização/métodos , Condutividade Elétrica , Campos Eletromagnéticos , Teste de Materiais , Conformação Molecular , Nanotubos/efeitos da radiação , Nanotubos/ultraestrutura , Transição de Fase , Titânio/análise , Temperatura de Transição
14.
J Nanosci Nanotechnol ; 5(10): 1741-4, 2005 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-16245539

RESUMO

Pure and well-crystallized Barium Strontium Titanate (BST) nanoparticles with controlled Ba/Sr ratio have been successfully synthesized under supercritical conditions using a continuous-flow reactor in the temperature range of 150-380 degrees C at 26 MPa. To synthesize the Ba0.6Sr0.4TiO3 composition, alkoxides, ethanol and water were used. The resulting nanopowder consists of fine particles with an average particle size of 23 nm. The results show that the Ba/Sr ratio of this powder can be accurately controlled from the composition of precursor. The characterization of the as-synthesized Ba0.6Sr0.4TiO3 solid-solution and the dielectric properties of the sintered ceramics are here reported.


Assuntos
Compostos de Bário/química , Cromatografia com Fluido Supercrítico/métodos , Cristalização/métodos , Magnetismo , Nanotubos/química , Nanotubos/ultraestrutura , Nitratos/química , Estrôncio/química , Compostos de Bário/análise , Condutividade Elétrica , Eletroquímica/métodos , Teste de Materiais , Nanotecnologia/métodos , Nanotubos/análise , Nitratos/análise , Tamanho da Partícula , Estrôncio/análise , Propriedades de Superfície
15.
J Nanosci Nanotechnol ; 5(6): 980-3, 2005 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-16060164

RESUMO

This work highlights, for the first time, the coating of ferroelectric nanoparticles with a chemical fluid deposition process in supercritical fluids. BaTiO3 nanoparticles of about 50 nm are coated with a shell of a few nanometers of amorphous alumina and can be recovered as a dry powder for processing. The sintering of these core-shell nanoparticles gives access to a ceramic material with very interesting ferroelectric properties, in particular, dielectric losses below 1%.


Assuntos
Óxido de Alumínio/química , Compostos de Bário/química , Cromatografia com Fluido Supercrítico/métodos , Compostos Férricos/química , Magnetismo , Nanotecnologia/métodos , Nanotubos/química , Nanotubos/ultraestrutura , Titânio/química , Adsorção , Óxido de Alumínio/análise , Compostos de Bário/análise , Cerâmica/análise , Cerâmica/química , Cristalização/métodos , Compostos Férricos/análise , Teste de Materiais , Nanotubos/análise , Tamanho da Partícula , Titânio/análise
16.
Appl Spectrosc ; 59(5): 639-49, 2005 May.
Artigo em Inglês | MEDLINE | ID: mdl-15969809

RESUMO

Thin film embodiments of MBa2Cu3O7-x (MBCO, M = yttrium or a rare-earth metal) prepared by several different deposition methods on a variety of substrates were investigated by Raman microspectroscopy. Several of the unique characterization capabilities of Raman spectroscopy in the analysis of MBCO thin films are highlighted by the results of these investigations. The Raman active phonons of the orthorhombic and tetragonal forms of MBCO that are most useful for characterization of textured MBCO films are diagrammed and discussed. A rapid procedure for qualitative texture mapping of MBCO thin films using Raman microscopy techniques is presented, and a new approach for investigating phase separation at the sub-micrometer level in MBCO thin films based on curve resolution of the MBCO Cu2 phonon is described. The assignment of a particular feature often observed in Raman spectra of MBCO films to cation disorder is reinforced by results of a cation substitution study. The depth of penetration of the laser into MBCO films and the type of information that can be obtained by varying the extent of defocusing of the laser are also discussed.


Assuntos
Compostos de Bário/análise , Compostos de Bário/química , Técnicas de Química Combinatória/métodos , Cobre/análise , Cobre/química , Cristalização/métodos , Membranas Artificiais , Análise Espectral Raman/métodos , Ítrio/análise , Ítrio/química , Cristalografia/métodos , Teste de Materiais/métodos , Metais Terras Raras/análise , Metais Terras Raras/química , Propriedades de Superfície
17.
Nat Mater ; 4(6): 476-80, 2005 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-15880116

RESUMO

Single-crystal superconductors of the general formula (LRE)-Ba-Cu-O (light rare earth, LRE = Nd, Sm, Eu and Gd) have considerable potential for engineering applications because of their ability to trap magnetic fields significantly higher than those achievable with permanent magnets. But the lack of a process by which these materials can be fabricated reliably and economically in the form of large single grains has severely hindered their development. We report a practical processing method for the fabrication in air of single-crystal (RE)BCO. The technique is economical and offers considerable freedom in terms of the processing parameters and reproducibility in growth of oriented single grains. The process is based primarily on the development of a new type of generic seed crystal that can effectively promote the epitaxial nucleation of any (RE)BCO system, and secondly on suppressing the formation of RE-Ba solid solution in a controlled manner within large grains processed in air.


Assuntos
Compostos de Bário/química , Cobre/química , Cristalização/métodos , Instalação Elétrica , Compostos de Bário/análise , Cobre/análise , Condutividade Elétrica , Teste de Materiais , Propriedades de Superfície , Temperatura Ambiente
18.
Nat Mater ; 4(6): 470-5, 2005 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-15908959

RESUMO

Practical high-temperature superconductors must be textured to minimize the reduction of the critical current density J(gb) at misoriented grain boundaries. Partial substitution of Ca for Y in YBa(2)Cu(3)O(7-delta) has shown significant improvement in J(gb) but the mechanisms are still not well understood. Here we report atomic-scale, structural and analytical electron microscopy combined with transport measurements on 7 degrees [001]-tilt Y(0.7)Ca(0.3)Ba(2)Cu(3)O(7-delta) and YBa(2)Cu(3)O(7-delta) grain boundaries, where the dislocation cores are well separated. We show that the enhanced carrier density, higher J(gb) and weaker superconductivity depression at the Ca-doped boundary result from a strong, non-monotonic Ca segregation and structural rearrangements on a scale of approximately 1 nm near the dislocation cores. We propose a model of the formation of Ca(2+) solute atmospheres in the strain and electric fields of the grain boundary and show that Ca doping expands the dislocation cores yet enhances J(gb) by improving the screening and local hole concentration.


Assuntos
Compostos de Bário/química , Cálcio/química , Cobre/química , Cristalização/métodos , Nanoestruturas/química , Semicondutores , Ítrio/química , Compostos de Bário/análise , Cobre/análise , Condutividade Elétrica , Instalação Elétrica , Campos Eletromagnéticos , Teste de Materiais , Conformação Molecular , Nanoestruturas/análise , Nanoestruturas/ultraestrutura , Propriedades de Superfície , Temperatura Ambiente , Ítrio/análise
19.
J Nanosci Nanotechnol ; 5(3): 394-6, 2005 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-15913244

RESUMO

Self-assembly of BaF2 nanoparticles was described. BaF2 nanoparticles were prepared by microemulsion technology. The self-assembly of the particles is spontaneous without coating reagent on the surface or external force being applied during the procedure of sample preparation. XRD examination and ICP data showed the phase purity of the final product; FTIR spectroscopy confirmed that there was no organic species leaved in the product. By depositing one drop of colloid solution containing BaF2 particles on the TEM grid directly, we can get the ring-like self-assembly with larger particles dispersing peripherally to form a ring and smaller particles inside this ring forming circles.


Assuntos
Compostos de Bário/química , Cristalização/métodos , Emulsões/química , Fluoretos/química , Nanotecnologia/métodos , Nanotubos/química , Compostos de Bário/análise , Emulsões/análise , Fluoretos/análise , Substâncias Macromoleculares/análise , Substâncias Macromoleculares/química , Conformação Molecular , Nanotubos/análise , Tamanho da Partícula , Propriedades de Superfície
20.
Guang Pu Xue Yu Guang Pu Fen Xi ; 21(3): 284-6, 2001 Jun.
Artigo em Chinês | MEDLINE | ID: mdl-12947646

RESUMO

An apparatus for cavity ringdown spectroscopy was constructed and used for atomic absorption measurement. The transition probability for 6s6p1P1<--6s6s1S0 transition of barium atoms was obtained in the self-made apparatus. The relation between atomic absorption coefficient and atomic oven temperature was also analysed.


Assuntos
Compostos de Bário/análise , Bário/análise , Lasers , Espectrometria de Massas/métodos , Sulfato de Bário/análise , Espectrometria de Massas/instrumentação , Metais/química , Estrutura Molecular , Processamento de Sinais Assistido por Computador
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