Connectivity and flux pinning improvements in Ag-clad BSCCO-2223 tapes produced by changes in the cooling rate
- PDF / 422,161 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 23 Downloads / 160 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Connectivity and flux pinning improvements in Ag-clad BSCCO-2223 tapes produced by changes in the cooling rate J. A. Parrella) and D. C. Larbalestier Applied Superconductivity Center and Materials Science Program, University of Wisconsin – Madison, 1500 Engineering Drive, Madison, Wisconsin 53706
G. N. Riley, Jr., Q. Li, W. L. Carter, R. D. Parrella, and M. Teplitsky American Superconductor Corporation, Westborough, Massachusetts 01581 (Received 17 April 1997; accepted 19 June 1997)
The rate at which Ag-clad (Bi, Pb)2 Sr2 Ca2 Cu3 Ox tapes are cooled from their final reaction heat treatment influences both the intergranular connectivity and intragranular flux pinning strength of the polycrystalline filaments. As the cooling rate from 825 ±C to 730 ±C in 7.5% O2 was decreased over a range of 5 ±Cymin to 0.005 ±Cymin, Jc (77 K, 0 T) increased from ,8 to ,24 kAycm2 , and the irreversibility field increased from ,120 to ,200 mT. The Jc (4.2 K, 0 T) increased in a similar fashion. Cooling slowly also sharpened the critical temperature transition and increased the critical onset temperature from 107 K to 109 K. These improvements in the superconducting properties occurred despite partial decomposition of the (Bi, Pb)2 Sr2 Ca2 Cu3 Ox phase into non-superconducting impurity phases during the slow cooling. A microstructural basis for these multiple effects is described.
I. INTRODUCTION
The superconducting properties of Ag-sheathed (Bi, Pb)2 Sr2 Ca2 Cu3 Ox (or “2223”) tapes are strongly dependent on several microstructural features which can determine the macroscopic critical current density, Jc , of the polycrystalline oxide filament(s). Jc is defined here in the usual macroscopic sense as the critical current Ic divided by the whole superconductor cross section. However, changes in Jc defined in this manner are not necessarily directly attributable to specific causes. For example, the grain alignment,1–7 bulk density,8–13 microcrack density,12,14–17 and phase purity18–21 are all factors that can impose limits on the grain-to-grain connectivity, and thus the macroscopic Jc of a 2223 tape. These properties are largely determined by specific details of the tape heat treatment and deformation processing sequence. Parrell et al. have previously shown22,23 that the rate at which 2223 tapes are cooled after heat treatment has a large effect on the transport Jc , irreversibility field (H*), critical temperature (Tc ) transition, and filament microstructure. They reported that slow cooling (,0.1 ±Cymin) in 7.5% O2 increased the Jc (77 K, 0 T) by as much as 300% over tapes more quickly cooled, considerably sharpened the Tc transition, and in some cases, increased the onset temperature by 1–2 K, despite
a)
Now at Oxford Superconducting Technology, 600 Milik Street, Carteret, New Jersey 07008. J. Mater. Res., Vol. 12, No. 11, Nov 1997
http://journals.cambridge.org
Downloaded: 18 Mar 2015
decomposition of the 2223 phase caused by cooling slowly at temperatures below the 2223 phase st
Data Loading...
