Determination of the oxygen and nitrogen interstitial diffusion coeficient in niobium by mechanical spectroscopy

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

Study of interstitial oxygen mobility in RuSr2GdCu2O8 by internal friction

The discovery of the spatial uniform coexistence of superconductivity and ferromagnetism in ruthenocuprates, RuSr2GdCu2O8 (Ru-1212), has spurred an extraordinary development in the study of the competition between magnetism and superconductivity. However, several points of their preparation process and characterization that determine their superconductive behaviour are still obscure. The improvement of sample preparation conditions involves some thermal treatments in inert atmosphere. Anelastic spectroscopy measurements were made using an inverted torsion pendulum, operating with an oscillation frequency of 38 Hz, temperature in the 90 and 310 K range, heating rate of 1 K/min, and vacuum better than 10(-3) Pa. The results show anelastic relaxation peaks at 210 K related to the presence of interstitial oxygen atoms. The peaks decrease significantly with the oxygen loss caused by the heat treatments in vacuum, appearing again after the annealing of the sample in an oxygen atmosphere. These observed peaks are clearly related to the additional oxygen atoms, with activation energy 0.13 and 0.36 eV, and can be explained in terms by diffusional jumps of interstitial oxygen in the RuO2 planes. (C) 2009 Elsevier B.V. All rights reserved.

Oxygen diffusion in superconducting oxides

Since the discovery of high-temperature superconductivity of cuprate oxides, it has been clear that it is strongly affected by the oxygen content, which is also a crucial factor to determine other physical properties of high T-c superconductors. Non-stoichiometric (interstitial) oxygen strongly influences the physical properties of various superconducting oxides, in particular by creating conducting holes. It is now ascertained that the amount of holes injected depends not only on the content of interstitial oxygen, but also on its ordering. Rearrangement of the oxygen ordering may occur even below room temperature due to the unusual high mobility of these atoms. This way, mechanical spectroscopy is one of the most adequate techniques for the study of the mobility (diffusion) of oxygen atoms. This technique allows the determination of the jump frequency of an atomic species precisely, regardless of the model or the different possible types of jumps. In order to evaluate the mobility and the effect of oxygen content on these oxides, ceramic samples we prepared and submitted to several oxygen removal cycles alternately with mechanical relaxation measurements. As for SBCO, it was assumed that the peak was due to O(1)-O(5) jumps of oxygen atoms at the chain terminals or in chain fragments in the orthorhombic phase. In the case of BSCCO, the results showed complex anelastic relaxation structures, which were attributed to interstitial oxygen atom jumps between two adjacent CuO planes.

Three-dimensional solitons in cross-combined linear and nonlinear optical lattices

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

Mechanical damping of the snoek peak in tantalum - Oxygen system

Interstitial solutes in body-centered cubic metals, such as oxygen in tantalum, produce ideally Snoek effects when they are in solutions enough diluted. However, for higher concentration of these solutes, more complex relaxation process can occur, as interaction between interstitial solutes and dislocations. Anelastic relaxation measurements were carried out in polycrystalline tantalum samples, using torsion pendulum inverted, operating between 300 K and 680 K and oscillation frequencies in the hertz bandwidth, for three different experimental sample conditions: as received sample, annealed and annealed followed by a treatment in an oxygen atmosphere. These measurements have revealed the following behavior: the intensity of the internal friction peak associated to matrix-interstitial interaction Ta-O decreased between the first run and the next runs, and this phenomenon did not occur for the others conditions. The variation of relaxation strength of Ta-O peak, with number of runs is due to a decrease of an amount of oxygen in solid solution, which can be associated with the precipitation of new phases in Ta sample and with the trapping of oxygen atoms by dislocations.

Diffusion phenomena of the oxygen and nitrogen in niobium by mechanical spectroscopy

The short-range diffusion phenomenon (Snoek Effect) was investigated by mechanical spectroscopy measurements between 300 K and 650 K, in a polycrystalline niobium sample, containing oxygen and nitrogen, using a torsion pendulum. Experimental spectra of anelastic relaxation were obtained under three conditions: as-received sample; annealed sample and subsequently annealed in an oxygen atmosphere for three hours at 1170 K in partial pressure of 5°10 -5mbar. The experimental spectra obtained were decomposed in elementary Debye peaks and the anelastic relaxation processes were identified. With anelastic relaxation parameters and the lattice parameters, the interstitial diffusion coefficients of the oxygen and nitrogen in niobium were calculated for each kind of preferential occupation (octahedral and tetrahedral). The results were compared with the literature data, and confirmed that the best adjustment is for the preferential occupation octahedral model for low concentrations of interstitial solutes, but at higher concentration of oxygen were observed deviations of experimental data for the interstitial diffusion coefficients of oxygen in niobium when compared with the literature data, this could be related to the possible occurrence of a double occupation of interstitial sites in the niobium lattice by oxygen interstitials. © (2010) Trans Tech Publications.

Mobilidade de oxigênio intersticial em SM'BA IND.2' C IND.U 'IND.3' 'O IND. 7-'delta' medida através de espectroscopia mecânica

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Efeito do nitrogênio nas propriedades anelásticas de Nb e ligas Nb-1,0%pZr

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Measurement of the rotational inertia of bodies by using mechanical spectroscopy

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

Three-dimensional solitons in cross-combined linear and nonlinear optical lattices

The existence and stability of three-dimensional (3D) solitons, in cross-combined linear and nonlinear optical lattices, are investigated. In particular, with a starting optical lattice (OL) configuration such that it is linear in the x-direction and nonlinear in the y-direction, we consider the z-direction either unconstrained (quasi-2D OL case) or with another linear OL (full 3D case). We perform this study both analytically and numerically: analytically by a variational approach based on a Gaussian ansatz for the soliton wavefunction and numerically by relaxation methods and direct integrations of the corresponding Gross-Pitaevskii equation. We conclude that, while 3D solitons in the quasi-2D OL case are always unstable, the addition of another linear OL in the z-direction allows us to stabilize 3D solitons both for attractive and repulsive mean interactions. From our results, we suggest the possible use of spatial modulations of the nonlinearity in one of the directions as a tool for the management of stable 3D solitons.

Dynamical Elastic Moduli of the Ti-13Nb-13Zr biomaterial alloy by mechanical spectroscopy

Dynamical Elastic Moduli of the Ti-13Nb-13Zr biomaterial alloy were obtained using the mechanical spectroscopy technique. The sample with heat treatment at 1170K for 30 minutes and water quenched with subsequent aging treatment at 670 K for 3 hours (TNZ + WQ + 670 K/3 h), was characterized through decay of free oscillations of the sample in the flexural vibration mode. The spectra of anelastic relaxation (internal friction and frequency) in the temperature range from 300 K to 625 K not revealed the presence of relaxation process. As shown in the literature, the hcp structure usually does not exhibit any relaxation due to the symmetry of the sites in the crystalline lattice, but if there is some relaxation, this only occurs in special cases such as low concentration of zirconium or saturation of the stoichiometric ratio of oxygen for zirconium. Dynamical elastic modulus obtained for TNZ + WQ + 670 K/3 h alloy was 87 GPa at room temperature, which is higher than the value for Ti-13Nb-13Zr alloy (64 GPa) of the literature. This increment may be related to the change of the proportion of α and β phases. Besides that, the presence of precipitates in the alloy after aging treatment hardens the material and reduces its ductility.

The use of Chebyshev matrix polynomials in the iterative solution of linear equations compared to the method of successive overrelaxtion /

"(This is being submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mathematics, June 1959.)"

Estágio de psicomotricidade em contexto de lar de infância e juventude e centro de atividades de tempos livres

O presente relatório refere-se ao estágio profissionalizante de Reabilitação Psicomotora, realizado no ano letivo 2014/ 2015, na Fundação O Século, em Lar de Infância e Juventude e Centro de Atividades de Tempos Livres. As crianças institucionalizadas pelas suas histórias de vida, apresentam fenótipos particulares, nomeadamente ao nível emocional, psicológico, do comportamento e da linguagem. A Dificuldade Intelectual e Desenvolvimental (DID) é uma perturbação do desenvolvimento que altera o funcionamento a nível cognitivo, motor, psicomotor, de linguagem e de funcionamento executivo. Foram dinamizadas sessões individuais com uma criança e um jovem com DID e um grupo. O estudo de caso reporta-se à criança com DID, com quem se desenvolveram sessões de psicomotricidade. Os instrumentos utilizados foram a Bateria Psicomotora e o Inventário Comportamental de Avaliação de Funções Executivas. Observou-se que a criança melhorou as competências psicomotoras, mas que houve uma manutenção nas Funções Executivas.

Measurement of oxygen atom diffusion in Nb and Ta by anelastic spectroscopy

Impurity interstitial atoms present in metals with BCC structure can diffuse in the metallic matrix by jumps to energetically equivalent crystallographic sites. Anelastic spectroscopy (internal friction) is based on the measurement of mechanical loss or internal friction as a function of temperature. Due to its selective and nondestructive nature, anelastic spectroscopy is well suited for the study of diffusion of interstitial elements in metals. Internal friction measurements were made using the torsion pendulum technique with oscillation frequency of a few Hz, temperature interval from 300 to 700 K, heating rate of about 1 K/min, and vacuum better than 10-5 mbar. The polycrystalline Nb and Ta samples used were supplied by Aldrich Inc. The results obtained showed thermally activated relaxation structures due to stress-induced ordering of oxygen atoms around the Nb (or Ta) atoms of the metallic matrix. The results were interpreted by three methods and led to activation enthalpy values for the diffusion of oxygen in Nb and Ta of 1.15 eV and 1.10 eV, respectively.

Thermo-optical characterization of tellurite glasses by thermal lens, thermal relaxation calorimetry and interferometric methods

In this work the thermal lens, thermal relaxation calorimetry and interferometric methods are applied to investigate the thermo-optical properties of tellurite glasses (in mol%: 80TeO(2)-20 Li2O(TeLi), 80TeO(2)-15Li(2)O-5TiO(2) (TeLiTi-5) and 80TeO(2)-10Li(2)O-10TiO(2) (TeLiTi-10)). Thermal diffusivity, thermal conductivity, specific heat and the temperature coefficients of refractive index, optical path length, thermal expansion and electronic polarizability were determined. The use of three independent methods was useful for a complete characterization of the studied tellurite glasses. In addition, our results showed that the thermal expansion coefficient and the temperature coefficient of the optical path length (dS/dT) were significantly modified with the introduction of titanium, which may be relevant for the application of these glasses in the photonic area. (c) 2006 Elsevier B.V. All rights reserved.