Toughening of the ceramic superconductor Bi-2223 with Ag

In an attempt to increase the toughness of the high temperature superconductor Bi1.5Pb0.5Sr2Ca2Cu3Ox (Bi-2223) we synthesised composites with three different filler morphologies of Ag. It is shown that Ag-addition improves Bi-2223 grain growth and reduces sample-porosity. Little effect on the mechanical strength is observed but the mismatch in thermal expansion coefficient induces a residual stress field at the filler matrix interface and allows toughening mechanisms to appear. This results in a clear post-peak behaviour when filler with high aspect ratio is used. The effect of the aspect ratio on the efficiency of the toughening mechanisms is studied

A model for the percolation effect in the magnetic susceptibility of HTSC composites

A simple model is proposed to explain the nature of the screening properties of superconducting composites. The percolation effect in the susceptibility and the maximum in shielding efficiency are interpreted as a consequence of the encapsulation of nonsuperconducting areas by the superconducting material. A three dimensional simulation based on site-bond percolation theory was conducted to test this model, using the calculated fraction of bonds that become superconducting at low temperatur

Dependence of the microstructure of Ag/BSCCO composites on filler content

In order to obtain high Tc superconducting materials with improved mechanical properties, Bi1,5Pb0,5Sr2Ca2Cu3Ox / Ag-composites with 3 different filler morphologies were successfully synthesised. It is shown that Ag-addition improves Bi-2223 grain growth and reduces sample-porosity. An alignment of the ceramic phase along the surface of the Ag was observed and the results of TEM, SEM, DTA and EDX mapping are discussed. Conclusions concerning the alignation-mechanisms based upon these observations are compared with popular models described in literature. Composites exhibit increased ductility and isostrain conditions are met. Little effect on the mechanical strength is observed but the mismatch in thermal expansion coefficient induces a residual stress field at the filler matrix interface and allows toughening mechanisms to appear, resulting in a clear post-peak behaviour. SEM pictures of whisker debonding, crack bridging and whisker pullout, all demonstrating a suitable filler-matrix interface, are included. The role of the filler morphology and the sequence of the processing steps on the toughening efficiency will be discussed

Rediscovery of the Timor Bush Warbler Locustella timorensis on Alor and Timor Wallacea: clarifying taxonomic affinities defining habitat and survey recommendations

The Timor Bush Warbler Locustella timorensis was first collected by Georg Stein on Mount Mutis, West Timor in 1932, but there have been no confirmed field observations since. Here we report on the discovery of a new population of bush warbler on Alor (9 September 2009), which prompted a search for, and subsequent rediscovery, of the nominate Timor Bush Warbler (20 December 2009) in Timor-Leste. We also undertook the first bush warbler searches in the mountains on Atauro Island, and the first ornithological exploration of the mountains of Pantar and Wetar islands. On Alor, at least 13 male bush warblers were heard singing from shrub and grass beneath woodland and forest edge at 859–1,250 m. On Timor, at least 40 males were heard during December, April and July from tall grassland below Mount Ramelau (1,720–2,100 m), Timor-Leste. The song structure of the Alor and Timor birds is similar, and close to Javan Bush Warbler L. montis of Java and Bali, as well as to recordings of Russet Bush Warbler L. mandelli of mainland Asia and Benguet Bush Warbler L. seebohmi from the Philippines. The song of the Alor bird is substantially higher pitched (mean min/max 3,233–4,980 kHz) than the Timor bird (2,928–4,761 kHz) and both are substantially higher pitched than Javan birds. Recordings of Russet Bush Warbler from mainland Asia are higher pitched than songs of all insular taxa, and the song of Benguet Bush Warbler is of a similar pitch to the Timor bird. Recent molecular studies have found that divergences between Javan Bush Warbler and the Russet Bush Warbler are slight, and the high degree of song similarity of the Alor and Timor populations to Javan Bush Warbler places them close to the Benguet Bush Warbler complex. The Timor Bush Warbler is recognised as ‘Near Threatened’ by IUCN, but this will require re-evaluation. On Alor, suitable habitat is extensive and under little threat, but grassland in the uplands of West and East Timor is intensively grazed and regularly burnt. Further field surveys are needed on both Timor and Alor to capture birds, clarify taxonomic relationships using molecular approaches, and further define habitat use and conservation status. Bush warblers were not recorded from Pantar, Atauro and Wetar islands

CeO2 dunne films via een waterige sol-gel methode : textuur en structurele eigenschappen

During the last decade the focus in superconductivity research has partly shifted towards coated conductors, because of their high usability in electronic applications in comparison to bulky ceramic superconductors. The presented work reviews some recent progress made in the bufferlayer structure of such coated conductors. We focused on waterbased CeO2 thin films prepared by the sol‐gel method and deposited via dipcoating. Starting from watersoluble cerium(III)nitrate precursors, we were able to deposit thin films showing a variable degree of 002 orientation dependant on the film characteristics and synthesis conditions. The main influencing parameters on attaining the desired texture seems to be the flowing rate of the ambient Ar / 5%‐H2 atmosphere and the thickness of the synthesized bufferlayers. We could achieve a 50nm thick CeO2 film, exhibiting a high degree of 002 orientation and low surface roughness

Chemical approach to the deposition of textured CeO₂ buffer layers based on sol gel dip coating

The widespread use of vacuum techniques for the development of coated conductors, in which buffer and superconducting (REBa2Cu3O7-delta) layers are deposited epitaxially on a substrate, is well established in the research environment. However, obtaining uninterrupted deposition at high speed, increasing flexibility in composition and in film thickness and attaining independence of geometric constraints are areas in which many vacuum techniques will need sustained development in order to answer industrial demands. This work describes the deposition of textured CeO2 buffer layers based on sol gel dip coating under atmospheric environment and from aqueous precursor materials. Research has been performed towards the deposition of CeO2-buffer layers using the amorphous citrate method on sapphire substrates and Ni-W foils. Coating is performed using the dip-coating technique, which allows extension to a continuous system. The withdrawal speed and the thermal treatment have been optimised in order to obtain highly oriented (001) layers exhibiting a smooth and crack-free morphology both on ceramic and metallic substrates, From the results it was concluded that sintering atmosphere and sintering temperature play a crucial role in the growth mechanism. This study describes the structural and morphological analysis of the thin layer with special attention to the difference between ceramic and metallic substrates

Low-field magnetoresistance in La0.7Ca0.3MnO3 manganite compounds prepared by the spray drying technique

peer reviewedCalcium-substituted lanthanum manganite compounds were synthesized by the spray drying technique. This method - whose main advantages are versatility, high reproducibility and scalability - yields small grain materials of high homogeneity and displaying low-field magnetoresistance effects. We report about the physical and chemical characterizations of these samples in order to investigate the potential interest of spray drying for the production of materials for low-field magnetoresistance applications. We have studied the dependence of the low-field magnetoresistance on the temperature and duration of the thermal treatment applied to the pelletized powders. The issue of the shape anisotropy (demagnetisation effects) influence on the magnetoresistance properties has also been dealt with. (C) 2005 Springer Science + Business Media, Inc