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Enhancement of critical current density in superconductor by mechanical deformation V. Selvamanickam, M. Mironova, and K. Salama Texas Center for Superconductivity, University of Houston, Houston, Texas 77004 (Received 13 March 1992; accepted 25 September 1992)

The critical current density of melt-textured YBa 2 Cu 3 0^ superconductor has been enhanced by mechanical deformation at a high temperature. Hot deformation at 45° to both the slip plane (001) and the slip directions [100]/[010] has resulted in a high density of dislocation loops and stacking faults. The deformed samples are found to exhibit a critical current density {Jc) at //||c-axis as high as that at H\\a-b plane at 1.5 T and 77 K. A Jc of 35300 A/cm 2 has been achieved at H\\c (1.5 T and 77 K) which is twice as high as that observed in undeformed samples. The enhanced Jc in this magnetic field orientation is attributed to pinning by the defects created by mechanical deformation. This pinning mechanism is found to be effective over a wide angle between the magnetic field and the a-b plane and thus results in a marked reduction in the critical current anisotropy.

I. INTRODUCTION The highest critical current densities in bulk YB32CU3O;,; superconductors have been reported in melt-textured materials.1"3 Current density in the order of 104 A/cm 2 has been achieved in melt-textured YBa 2 Cu 3 () I at 77 K in magnetic fields of several Tesla4'5 when the field is applied parallel to the strongly superconducting a-b planes (H\\a-b). Such high current densities in this magnetic field orientation have been attributed to intrinsic pinning in both melt-textured bulk materials6 and thin films.7 However, when the magnetic field is applied perpendicular to the a-b plane (H\\c), the current density drops rapidly with the application of a few Tesla and vanishes at the irreversibility field of about 7 T at 77 K.8 Such a drastic decay in current density has been ascribed to the inherent magnetic anisotropy in high temperature superconductors and to a weak pinning potential. Since the low current density in the orientation of H\\c will be a limiting factor in several applications, it is necessary to develop improved processing methods for melt-textured YBa 2 Cu 3 0 x to enhance the current density in this magnetic field configuration. Modification in the microstructure of melt-textured YBa2Cu30A: has been attempted by addition of nonsuperconducting phases such as Y2BaCuO5,9>10 BaSnO 3 , n Ag,12 and Pt.13 Though some microstructural refinement is observed by second-phase additions, their contribution to pinning has been unclear. Fast neutron irradiation of melttextured samples has also resulted in critical current improvement,14 but the enhancement factor has been low when the Jc of unirradiated pristine samples is high.15 More importantly, the feasibility of this process in largescale production is still questionable. J. Mater. Res., Vol. 8, No. 2, Feb 1993 http://journals.cambridge.org

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In this study we have developed a processing method to enh