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Bulk superconductors textured and densified by Spark Plasma Sintering J. G. Noudem1,2*, L. Dupont 3 and P. Bernstein1, 1 CRISMAT 2

CNRS-UMR6508-ENSICAEN 6 bld Mal Juin 14050 Caen Cedex 04 France LUSAC EA-4253, Université de Caen, Rue Louis Aragon, BP 78, 50130 CHERBOURG-OCTEVILLE, France 3 CAYLAR, 14 rue du Québec, 91140 Villebon-sur-Yvette, France *Email : [email protected] ; fax : +33 231 451 366 ABSTRACT In this contribution, we report progress in the preparation of superconducting materials made by Spark Plasma Sintering (SPS). On the one hand, the fabrication process was optimized in order to improve the texturing of Bi2Ca2Sr2CuO8 superconductor ceramics. The new process is referred to as “Spark Plasma Texturing” (SPT). During SPT, the bulk material is free to deform itself. As a result, an inter-grain preferential crystallographic orientation is generated, while materials processed by conventional SPS are usually quasi-isotropic. The crystallographic orientation causes a strong anisotropy in the magnetic properties of the Bi2Ca2Sr2CuO8 bulk. On the other hand, superconducting MgB2 discs were consolidated using the rapid SPS process. MgB2 has not been yet been seriously considered as a superconductor that could be used for magnetic levitation. Here we present trapped field measurements as a function of the distance to the superconductor and field cooled levitation force measurements that suggests that it presents interesting characteristics for this application. INTRODUCTION Texturing Bi2Sr2CaCu2O8 (Bi: 2212) and densifying MgB2 are essential to enhance the material properties. Several techniques of texturing and densification based on Hot Pressing (HP) or Hot-forging, Hot Isostatic Pressing (HIP), Magnetic Melt Texturation (MMT), Spark Plasma Sintering (SPS) etc1-7 have been successfully used to fabricate MgB2 and Bi: 2212 ceramics. Each process presents advantages and disadvantages from the point of view of practical applications. In this contribution, we focus on the SPS technique. We first describe the processes devised i) for hot-forming dense and textured Bi: 2212 and ii) for preparing dense MgB2 bulks. Secondly, we report some superconducting properties of the obtained materials. EXPERIMENTAL DETAILS The Bi: 2212 powder was prepared from oxides and carbonates precursors by using conventional solid-state reaction and cold pressed uni-directionally at 60 MPa into pellets with a diameter of 13 mm. The pellets were conventionally sintered at 700°C for 2 h in air and placed at the centre of a 20 mm diameter graphite die in order to ensure the free deformation and texturing of the sample. The final processing was carried out using a Spark Plasma Sintering system (namely FCT HD 25). Electric current pulses (2000 A, 4 Volts) were passed through the sample in vacuum (10-3 bar) during 10 minutes with the result of heating the samples at 750 °C, while an uniaxial pressure of 50 MPa was applied. During this step of the process, the temperature, the applied pressure and the displacement or skrinkage of the