Fabrication and characterization of highly textured (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x superconducting ceramics using high mag
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R. Stevens School of Materials Science, University of Bath, Bath BA2 7AY, United Kingdom
R. Doyle, A.M. Campbell, and W. Y. Liang IRC in Superconductivity, Madingley Road, Cambridge CB3 OHE, United Kingdom (Received 22 July 1994, accepted 15 June 1995)
High textured (Bi, Pb)2Sr2Ca2C~30s ceramics have been fabricated by aligning deflocculated flakes of (Bi, Pb)2Sr2Ca2Cu30, suspended in an organic medium by means of a high dc magnetic field (6 T) at room temperature followed by cold isostatic pressing. The proportion of the (Bi, Pb)2Sr2Ca2Cu30x phase in the precursor powder was carefully controlled, and the characteristics of the powder, such as size distribution and morphology, were determined. A high degree of grain alignment was found in the specimens after the magnetic alignment, although the bulk density of the materials was low. Cold isostatic pressing substantially increased the density of the magnetically prealigned specimens which also resulted in a slight decrease in the degree of grain alignment. This minor realignment was found to be due to the various kinds of processing defects that appeared in the specimens during compaction due to the grinding and cracking of the grains and their interlocking. The microstructural and superconducting properties of the sintered ceramic have been studied using texture goniometry, high resolution scanning electron microscopy, transmission electron microscopy, ac magnetic susceptometry, and critical current measurements.
I. INTRODUCTION
A high degree of grain alignment together with grain connectivity have been shown to be significant factors in attempts to control the critical current density of (Bi, Pb)2Sr2Ca2Cu30s(BSCCO 2223 phase) ceramic superconductor^.'-^ In addition, the fabrication of a highly textured 2223 phase ceramic is considered to be important for the study of the intragranular properties of this highly anisotropic compound, where properties such as the magnetic flux line structures, the flux line lattice properties, and the intrinsic flux pinning mechanisms are to be investigated, since all attempts to grow 2223 phase single crystals have been proved to be in vain. A highly textured 2223 phase ceramic is essential for the study of the influence of texturing on the properties of the intergranular critical state^,^ which in turn is crucial to the understanding of the superconducting transport properties of 2223 phase silver clad tapes. A knowledge of the intragranular and intergranular superconducting transport properties will form the basis of the conceptual design of this material for practical engineering applications. Making use of the limited pseudo-plasticity, the fracture behavior, and anisotropic magnetic properties of the 2223 phase superconducting grains, together with the J. Mater. Res., Vol. 10, No. 10, Oct 1995 http://journals.cambridge.org
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texturing of a ceramic sample, can be modified by means of two or more techniques. The first involves an application of mechanical stress to a precursor powder, encapsulated by d
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