Critical Current Properties and Microstructures of Ag-Sheathed Bi-Based Superconducting Wires
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MAGNETIC FIELD (T)
Experimental Details Bi2O3, PbO, SrCO3, CaCO3, and CuO powder with 4 to 5N purity whose cation ratios are Bi:Pb:Sr:Ca:Cu =
52
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Figure 2. jt(B) properties of tapes in a low magnetic field at 77 K.
1.8:0.4:2.0:2.2:3.0 were mixed, sintered and ground. Sintering between 750°C and 860°C for several hours and grinding were repeated several times. The powder was put into silver tubes, drawn into round wires and then made into tape-shaped wires by rolling or pressing. These tapes were sintered twice with a rolling or pressing process between them to develop
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MAGNETIC FIELD (T)
T. Kato, T. Hikata, M. Ueyama, K. Sato, and Y. Iwasa Introduction Since the first report of superconductivity in the Bi-Sr-Ca-Cu-O (BSCCO) system by Maeda et al, an enormous quantity of material work has been reported on the Bi system.12 The Bi-2223 phase exhibits a zero-resistivity temperature of around 110 K and this is the highest critical temperature outside the 125 K critical temperature found in the Tl-Ba-Ca-Cu-O system. The layered BSCCO phases cleave easily, making it possible to align grains by a deformation process. The powder-in-tube method is one of the fabrication processes that permits grain alignment and the achievement of high critical current density.3"6 This tendency is particularly strong for the 2223BSCCO phase. In this paper, we report on the relation between the critical current density (Jc) and the microstructure in silver-sheathed Bi-Pb-Sr-Ca-Cu-O (2223) wires produced by the powder-in-tube method.
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Figure 1. ]C(B) properties of tapes with the magnetic field applied parallel to the broad tape surface at 77 K.
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a higher critical current density. The typical size of the tapes was 0.15 mm thick and 4.0 mm wide. The JC(B) properties were evaluated using the transport current technique with the 4-probe dc method using a criterion of 1 /JV/cnx to define Jc. Transport JC(B) characteristics were evaluated at 77 K in magnetic fields from zero to 3 T. The Hirr(T) data were measured at the Francis Bitter National Magnet Laboratory with the facility's 33 mm warm bore, 30 T hybrid magnet. The magnetic field at which 1 (M cm was detected with a constant applied current of 200 mA was defined as H,rr.7 Microstructures of the wires were investigated by transmission electronmicroscopy (TEM) and scanning electron microscopy (SEM) and by energy-dispersive x-ray spectroscopy (EDX). Results and Discussion Figure 1 shows the JC(B) properties at 77 K of the tapes having a Jc ranging from 5.5 X 103 A/cm2 to 5.37 X 104 A/cm2 when the magnetic field was applied parallel to the tape surface. We find that the field dependence of Jc declines as the magnitude of Jc improves, particularly in weak fields below about 500 Gauss. Figure 2 shows the JC(B) properties of various samples in weak fields. Little decrease of Jc in the high Jc sample was observed, in contrast to a large decrease of a low Jc sample. The lower Jc samples have a history-dependent critical current density that is though
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