250 resultados para Dielectric spectroscopy
Resumo:
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Resumo:
The possibility of mechanochemical synthesis of the lead magnesium niobate (PMN) powders of the composition Pb(Mg(1/3)Nb(2/3))O(3) in iron vials was investigated. According to X-ray and energy-dispersive spectroscopy (EDS) analysis of the obtained powder mixtures, milling in iron vials resulted in incorporation of Fe and formation of PFN of composition Pb(Fe(1/2)Nb(1/2))O(3) simultaneously with formation of PMN. Relative amounts of PMN and PFN were determined based on values of Curie temperature and lattice constant of perovskite phase. Although only 1 wt pct of Fe was incorporated, a stoichiometry of the system was significantly changed, resulting in formation of pyrochlore phase and excess MgO. Single-phase perovskite was obtained when the excess of PbO and Nb(2)O(5) was added during mechanochemical synthesis. Because the dielectric properties were worse than expected, the alternative ways for improvement of dielectric properties were tried and discussed.
Resumo:
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Resumo:
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Resumo:
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Resumo:
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Resumo:
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Resumo:
We calculate the spectrum of the masses of light and heavy mesons, using a potential that shows confinement and asymptotic freedom for quark-antiquark pairs. From the analysis of the results we estimate the masses of mesons with hottom not yet found experimentally. We discuss the behaviour of the confinement potential under Lorentz transformation and calculate the spin-dependent corrections. We also calculate the electromagnetic decay rates and the leptonic and hadronic decay widths for some mesons. © 1985 Società Italiana di Fisica.
Resumo:
Eu3+ fluorescence spectroscopy was used as a probe to study the changes in local arrangements of tin oxyhydroxide precipitate → sol → gel → glass conversion. Electronic transition intensities and 5D0 excited state lifetime variations were followed during the entire process. Adsorption of Eu3+ ions on the colloid and changes of chemical interactions occurring in each step are described. © 1992 Elsevier Science Publishers B.V. All rights reserved.
Resumo:
A quark-diquark approximation is used to investigate the mass spectroscopy of the spin-1/2 baryons belonging to the SU(3)-flavor group in a nonrelativistic potential approach. The baryon spectra obtained are confronted with relativistic results and experimental data. Root-mean-square radii are also calculated. © 1993 Springer-Verlag.