Solid-state processing and phase development of bulk (MgO) w /BPSCCO high-temperature superconducting composite
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Solid-state processing and phase development of bulk (MgO)wyBPSCCO high-temperature superconducting composite Y. S. Yuan,a) M. S. Wong, and S. S. Wang Department of Mechanical Engineering and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204-4792 (Received 21 February 1995; accepted 29 September 1995)
The inherently weak mechanical properties associated with monolithic high-temperature superconductors (HTS) can be improved by introducing properly selected strong ceramic whiskers into the HTS materials. In this research, processing and superconducting properties of monolithic Pb-doped Bi-2223 (BPSCCO) and MgO whisker-reinforced BPSCCO HTS composite materials have been systematically studied. A solid-state processing method is successfully developed to fabricate the (MgO)wyBPSCCO composite. The HTS composite contains a dense and highly pure BPSCCO matrix phase with a preferred grain orientation, which is reinforced by MgO whiskers randomly oriented in the plane perpendicular to the hot-pressing direction. The HTS composite material is shown to exhibit excellent superconducting properties. For example, a transport Jc measured at 77 K in a zero field has been obtained to exceed 5000 Aycm2 in a (MgO)wyBPSCCO composite with 10% MgO whiskers by volume. Relationships among solid-state processing variables, HTS phase development, and superconducting properties of the monolithic BPSCCO and the HTS composite are established in the paper.
I. INTRODUCTION
The discovery of high-temperature superconductors (HTS) in cuprates1–5 has provided a real possibility of future practical applications. Significant efforts have been made in the past few years to improve the superconducting properties of the HTS materials, especially the critical current density (Jc ), to meet requirements for important bulk applications. With a significant amount of progress and understanding being achieved in processing and characterizing the HTS materials, further utilizations of these materials have been recognized; and limited small-scale prototypes may now become feasible, including, for example, superconducting energy storage systems,6 magnetic bearings,7 cryogenic current leads,8 and fault current limiters.9 In these applications, superconducting components are known to be employed in cryogenic environments, where strong magnetic and/or electrical fields are commonly present. Induced electromagnetic and thermomechanical stresses as well as associated deformations are expected in the HTS materials. Thus, in addition to retaining desirable superconducting properties, these materials are required to be physically strong, capable of sustaining long-term or cyclic thermomechanical loading, and to possess a bulk form with required dimensional stability. Despite their excellent superconducting properties, monolithic HTS a)
Currently with General Plastics & Rubber Company, Houston, Texas 77087.
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http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 1, Jan 1996
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