Microstructure and properties of Cu-rich 123: Part II. Homogeneous copper and high magnetic J c
- PDF / 1,819,693 Bytes
- 8 Pages / 576 x 791 pts Page_size
- 73 Downloads / 184 Views
C. H. Lin and J. A. Eades Science and Technology Center for Superconductivity, Materials Research Laboratory, University of Illinois at Champaign- Urbana, 104 South Goodwin, Urbana, Illinois 61801
A. Sodonis, W. Wolbach, J. M. Chabala, and R. Levi-Setti Science and Technology Center for Superconductivity, The Enrico Fermi Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637 (Received 2 April 1992; accepted 19 January 1993)
Copper- and yttrium-rich YBa 2 Cu 3 0 7 bulk superconductors have been prepared by mixing copper oxide or yttrium oxide in nitric acid and adding the solution to premade stoichiometric YBa 2 Cu 3 07 followed by annealing. In contrast to materials made by mixing oxide powders, both samples contain copper-rich defects spread homogeneously throughout the grains, either small platelet copper oxide precipitates or bundles of planar defects ( C u - 0 double planes). These materials also show large magnetic hysteresis at 77 K, comparable to the results obtained from decomposed YBa 2 Cu 4 08. This implies that small copper oxide precipitates and bundles of planar defects are strong flux pinners, and indicates a processing route to producing large amounts of strongly intragranular pinned superconductors. However, the materials also show clean grain boundaries, so an equally valid interpretation is that there is a substantial component of intergranular superconductivity in field, enhancing the effective circuit size to a value far larger than the grain size.
I. INTRODUCTION Perhaps the most important materials challenge in high temperature superconductors is producing a bulk material with good properties at 77 K. This is in fact two problems: solving the problem of weak links at the grain boundaries and solving the problem of flux pinning within the grains of the material. Although eventually both of these will have to be solved simultaneously, it is easier to approach them one at a time, and our concern herein is with the latter. A very attractive analogy to heterogeneous flux pinning (as against intrinsic, homogeneous flux pinning) within a grain is dispersion strengthening of a material, i.e., use of small secondphase precipitates to reduce flux flow. The type of questions to be answered are what type of precipitates and what morphologies are optimal for flux pinning; this type of information can then be used to try to design a superconductor. In an earlier paper,1 we reported in some detail the microstructure and Bean model critical current results of a set of copper-rich samples produced by mixing the elemental oxides and annealing. In these samples the copper was restricted to the grain boundary region, 1232
J. Mater. Res., Vol. 8, No. 6, Jun 1993
http://journals.cambridge.org
Downloaded: 15 Mar 2015
and although there was a small enhancement in Jc at 4.5 K compared to a control sample, at 77 K the results were slightly worse. These results indicated that copper at the grain boundaries alone is not a good flux pinner. In this note, we report results using a d
Data Loading...
