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 $La_{0.7}Ca_{0.3}Mn_{1-x}Cu_xO_3$ has been observed at slight $Cu$ doping ($0\leq x \leq 0.05$). Namely, introduction of copper results in a splitting of the resistivity maximum around a metal-insulator transition temperature $T_0(x)$ into two differently evolving peaks. Unlike the original $Cu$-free maximum which steadily increases with doping, the second (satellite) peak remains virtually unchanged for $x<x_c$, increases for $x\ge x_c$ and finally disappears at $x_m\simeq 2x_c$ with $x_c\simeq 0.03$. The observed phenomenon is thought to arise from competition between substitution induced strengthening of potential barriers (which hamper the charge hopping between neighboring $Mn$ 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