84 research outputs found
The contribution of 211 particles to the mechanical reinforcement mechanism of 123 superconducting single domains
Hardness and fracture toughness of Dy-123 single-domains were studied by
Vickers micro-indentation. A significant anisotropy of the mechanical
properties was observed. Hardness tests give higher values when performed in
(001) planes rather than in planes parallel to the c-axis. Moreover cracks
pattern around the indentation follows preferential orientation in planes
parallel to the c-axis whereas a classical ''four-cracks'' pattern is observed
in the (001) planes. It has been possible to show the crucial role played by
the 211-particles in the deviating mechanism of cracks and the relevance of the
211-particle distribution high homogeneity in the material.Comment: 14 pages, including 5 figures and 1 Table. submitted to Supercond.
Sci. Techno
Influence of the shaping effect on hardness homogeneity by Vickers indentation analysis
In this study, indentation technique (Vickers indentation) has been unconventionally used to evaluate the homogeneity of barium zirconate ceramic samples which have been shaped through different routes. Statistical tools have been used to estimate the con-elation which can be established between heterogeneities within the samples and their shaping ways. (c) 2005 Elsevier Ltd. All rights reserved
Anomalous temperature behavior of resistivity in lightly doped manganites around a metal-insulator phase transition
An unusual temperature and concentration behavior of resistivity in
has been observed at slight doping
(). Namely, introduction of copper results in a splitting of
the resistivity maximum around a metal-insulator transition temperature
into two differently evolving peaks. Unlike the original -free
maximum which steadily increases with doping, the second (satellite) peak
remains virtually unchanged for , increases for and finally
disappears at with . The observed phenomenon
is thought to arise from competition between substitution induced strengthening
of potential barriers (which hamper the charge hopping between neighboring
sites) and weakening of carrier's kinetic energy. The data are well fitted
assuming a nonthermal tunneling conductivity theory with randomly distributed
hopping sites.Comment: 10 REVTEX pages, 2 PostScript figures (epsf.sty); to be published in
JETP Letter
Importance of soft solution processing for advanced BaZrO3 materials
peer reviewedBarium zirconate is an interesting material for refractory applications as well as a good substrate for the manufacturing of high temperature superconductors. However, its solid state synthesis requires high temperature and provides inhomogeneous powder with a broad particle size distribution. In order to avoid these disadvantages, soft solution routes are of growing importance in the ceramic powder synthesis. Precipitation. decomposition of precursors, combustion techniques offer alternative ways to the solid state method. Advantages of these are a lower calcination temperature, production of homogeneous and fine monodisperse powders. The obtained powders have been characterised by XRD, IR, SEM and DTA/TG analysis. The influence of the synthesis conditions on the properties of BaZrO3 has been studied. (C) 2001 Elsevier Science Ltd. All rights reserved
YBa2Cu3O7 tapes prepared by sol-gel deposition techniques: microstructure and structural characterizations
We report on the preparation conditions of YBa2Cu3O7 polycrystalline superconducting tapes by a sol-gel deposition technique. We present some discussion on the compatibility between the nature of the substrate, the use of a buffer layer, and the conditions used to prepare appropriate superconducting YBa2Cu3O7,, materials. We report also on the microstructural characterizations performed in order to evaluate the crystallites size, degree of orientation and connectivity. (C) 2002 Elsevier Science B.V. All rights reserved
Raman Spectroscopy of Some Basic Chloride Containing Minerals of Lead and Copper
Raman spectroscopy has been used to characterise several lead and mixed cationic-lead minerals including mendipite, perite, laurionite, diaboléite, boléite, pseudoboléite, chloroxiphite, and cumengéite. Raman spectroscopy enables their vibrational spectra to be compared. The low wavenumber region is characterised by the bands assigned to cation-chloride stretching and bending modes. Phosgenite is a mixed chloride-carbonate mineral and a comparison is made with the molecular structure of the aforementioned minerals. Each mineral shows different hydroxyl-stretching vibrational patterns, but some similarity exists in the Raman spectra of the hydroxyl deformation modes. Raman spectroscopy lends itself to the study of these types of minerals in complex mineral systems involving secondary mineral formation
Preparation of nanosized barium zirconate powder by thermal decomposition of urea in an aqueous solution containing barium and zirconium, and by calcination of the precipitate
The synthesis of barium zirconate was initiated by urea induced homogeneous precipitation followed by a "low temperature" thermal treatment. The kinetic of the reaction and the optimum urea/cation ratio have been determined by means of X-ray diffraction and Inductive Coupled Plasma analyses. It has been demonstrated that an amorphous zirconium hydrated oxide starts to precipitate followed by the precipitation of barium carbonate. A calcination at 1200 degreesC during 2 h gives rise to the formation of a pure barium zirconate phase. Microstructural characterisations have been performed in order to evaluate the sintering behaviour. Dilatometric measurements, coupled with scanning electron microscopy analyses clearly indicate that barium carbonate decomposition process leads to the formation of internal porosity which severely limits the density of the material, even if a sintering was performed at 1500 degreesC. A careful control of the heating profile seems to be necessary in order to produce dense materials. (C) 2003 Elsevier Ltd. All rights reserved
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