Transport critical current density above 10(5) A cm(-2) at 77 K in Bi1.8Pb0.4Sr2.0Ca2.2Cu3.0Oy superconducting tapes made by the Ag wire-in-tube method

Transport critical current density (J(c)) is a limiting factor in the practical application of (Bi,Pb)(2)Sr2Ca2Cu3Oy (BSCCO-2223) high-temperature superconducting materials. The minimum requirement is for a J(c) of 10(5) A cm(-2) in long wires and tapes, at 77 K and in a high magnetic field. The issue of current distribution inside Ag-sheathed tapes has been resolved by showing that the region of high critical current density is next to the silver. In this paper we report a J, value > 10(5) A cm(-2) at 77 K in a self-field in Bi1.8BPb0.4Sr2.0Ca2.2Cu3.0Oy superconducting tapes made by the Ag wire-in-tube method, in which a silver wire was introduced into the silver tube. The silver wire extended along the entire length of the tape and reduced the difference between the nominal cross section of the superconductor and its actual current-carrying cross section. At 77 K and self-field, a maximum J(c) of 2 x 10(5) A cm(-2) (critical current I-c = 22 A) was measured after three pressing cycles at 800 degrees C in a 7% O-2 atmosphere. The average thickness of the superconducting layer between the sides of silver layers was in the order of 1-2 mu m and the width was 3.6 mm. This study confirms that the current-carrying region in BSCCO tapes is the layer adjacent to the Ag sheath. Previously it was shown that the superconductor core for thicker superconductor layers (similar to 70 mu m) does not carry significant current.