Anelastic Relaxation Measurements in Nb-46wt%Ti Alloys with Interstitial Solutes in Solid Solution

Anelastic relaxation measurements were performed in a Nb-46wt%Ti alloy, in the temperature range of 300 to 700 K, using a torsion pendulum operating at an oscillating frequency near 2.0 Hz. The samples were measured in different conditions: cold worked, annealed in ultra-high vacuum and doped with several quantities of nitrogen. The relaxation spectra obtained were resolved into their component peaks, corresponding to the different kinds of interaction of the interstitial solutes with the metallic matrix. The relaxation parameters of each process were calculated using Debye's elementary peaks.

Electrical relaxation in proton conductor composites based on (NH4)H2PO4/TiO2

We report on electrical relaxation measurements of (1-x)NH4H2PO4-xTiO(2) (x = 0.1) composites by admittance spectroscopy, in the 40-Hz-5-MHz frequency range and at temperatures between 303 and 563 K. Simultaneous thermal and electrical measurements on the composites identify a stable crystalline phase between 373 and 463 K. The real part of the conductivity, sigma', shows a power-law frequency dependence below 523 K, which is well described by Jonscher's expression sigma' = sigma(0)(1 + (omega/omega(p))(n)), where sigma(0) is the dc conductivity, omega(p)/2 pi = f(p) is a characteristic relaxation frequency, and n is a fractional exponent between 0 and 1. Both sigma(0) and f(p) are thermally activated with nearly the same activation energy in the II region, indicating that the dispersive conductivity originates from the migration of protons. However, activation energies decrease from 0.55 to 0.35 eV and n increases toward 1.0, as the concentration of TiO2 nanoparticles increases, thus, enhancing cooperative correlation among moving ions. The highest dc conductivity is obtained for the composite x = 0.05 concentration, with values above room temperature about three orders of magnitude higher than that of crystalline NH4H2PO4 (ADP), reaching values on the order of 0.1 (Omega cm)(-1) above 543 K.

Oxygen mobility in Bi:Sr:Ca:Cu:O ceramic measured using anelastic relaxation methods

Since the discovery of YBaCuO, experiments have shown that its superconducting properties are strongly affected by the oxygen content. More recently, anelastic relaxation measurements in La2CuO4+δ, showed that the decrease in the oxygen content can be related to two events. One is the decrease in mobility between two adjacent CuO planes, and the other is the increase in the number of tilting patterns of the CuO6 octahedra. In the case of the bismuth-based ceramic, it is known that the oxygen content, within some limits, does not affect its superconducting properties. In order to evaluate the mobility and the effect of the oxygen content on this material we have prepared BSCCO ceramic and tested regarding its internal friction and electrical resistivity as a function of the temperature while the oxygen content was being reduced by a sequence of vacuum annelaing at 620 K. The samples were prepared in the Bi:Sr:Ca:Cu = 2212 and 2223 proportion, using powder obtained by the sol-gel route and conventional solid state reaction. The anelastic relaxation measurements were performed using a torsion pendulum operating with frequency about 15-35 Hz between 77 to 700 K. The diffraction pattern of the as sintered and the vacuum annealed material were also presented. The results have shown complex anelastic relaxation structures that were associated to the jump of interstitial oxygen atoms between two adjacent CuO planes. The vacuum annealing showed to be deleterious to the critical temperature of the superconducting ceramic.

Anelastic spectroscopy in SmBa2Cu3O7

The possibility of variable stoichiometry and the high mobility of oxygen in the CuOx planes of SmBa2Cu3O7 give rise to a rich phase diagram. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature can distinguish among the different atomic jumps, which occur in the various phases or at different local ordering. In this paper, it is reported anelastic relaxation measurements in SmBa2Cu3O7, above room temperature, using a torsion pendulum operating in frequencies around 40 Hz. The mobility of oxygen atoms in the CuOx planes in the various phases has been discussed and the thermally activated peak of elastic energy dissipation observed around 500 K was interpreted in that framework. (C) 2004 Elsevier B.V. All rights reserved.

Mobilidade de oxigênio intersticial em cerâmicas SmBa2Cu3O7-delta

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

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.

Anelastic spectroscopy in TiO2

Titanium dioxide (rutile) has a lot of interesting and useful features and hence is widely utilized for application. It has been used as white pigment, photocatalyst, biocompatible material and semiconductor material used in solar battery. In semiconducting TiO2 oxygen vacancies are said to play an important role in the electrical conduction. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature can distinguish among the different atomic jumps, which occur in the various phases or at different local ordering. In this paper, it is reported anelastic relaxation measurements in TiO2 samples using a torsion pendulum operating in frequencies around 40Hz, in the temperature range between -173°C to 330°C with heating rate of 1°C/min. The results shown a reduction in the elasticity modulus with the increase in the corn starch content used for this consolidation.

Anelastic spectroscopy in Al2O3

Engineering ceramics have found use in many applications, such as engine parts, ball bearings, artificial bone and hip replacements and gyroscopes, because of their good chemical inertness, hardness, high temperature stability and excellent wear resistance. Oxide ceramic may meet these demands. Alumina (Al2O3) ceramics offer a high potential for many engineering applications, such as wear- and/or corrosion-resistant components, and as material for substrates or housings in microelectronic devices. Alumina is used among other things for seal ring, draw-cones, guides, water mixing tapes, bearing parts, medical prostheses and cutting tools. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature can distinguish among the different atomic jumps, which occurs in the various phases or at different local ordering. In this paper, it is reported anelastic relaxation measurements in Al2O3 samples using commercial starch. These measurements were carried out in a torsion pendulum operating in frequencies around 40 Hz. The results shown strongly influence of the type of forming in the elastic modulus obtained by anelastic relaxation measurements.

Anelastic spectroscopy in superconducting oxides

Since the discovery of the high Tc superconductors, several works have been made about the different properties of these materials. Anelastic spectroscopy experiments are sensitive tools to the study of defects in solids and phase transitions. By this technique, we can distinguish the different types of atomic jumps that happen to different temperatures. The intensity of the peaks in the anelastic spectrum and the step in the torsional modulus are related with the concentration of the relaxing entities, and the position of the peaks is determined by its mobility. In this paper, the study on Bi and Sm based superconducting oxides was made by anelastic relaxation measurements using a torsion pendulum. The samples were submitted to successive thermal treatments in high vacuum, in the temperature range between 100 K and 650 K, heating rate about 1 K/min. For Bi based superconducting oxides the results shown two peaks, that were associated to interstitial oxygen mobility and to orthorhombic to monoclinic phase transition. For Sm based superconducting oxides the results shown a relaxation peak that was attributed to the jumps of the oxygen atoms in the inter-chains O1 and 05 of the lattice.

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.

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

Investigation of microwave dielectric relaxation solid state process in the antiferroelectric phase of NaNbO3 ceramics

This letter reports microwave dielectric measurements performed in the antiferroelectric phase of NaNbO3 ceramics from 100 to 450 K. Remarkable dielectric relaxation was found within the antiferroelectric phase and in the vicinity of the ferroelectric-antiferroelectric phase transition. Such dielectric relaxation process was associated with relaxations of polar nanoregions with strong relaxor-like characteristic. In addition, the microwave dielectric measurements also revealed an unexpected and unusual anomaly in the relaxation strength, which was related to a disruption of the antiferroelectric order induced by a possible AFE-AFE phase transition. (C) 2004 Elsevier Ltd. All rights reserved.

The semi-synthetic kaurane ent-16 alpha-methoxykauran-19-oic acid induces vascular relaxation and hypotension in rats

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

Anelastic relaxation due to hydrogen in Ti-35Nb-7Zr-5Ta alloy

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Photo-Induced Dipole Relaxation Current in Natural Amethyst

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)