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-tempe rature 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 mag netic field. The issue of current distribution inside Ag-sheathed tape s has been resolved by showing that the region of high critical curren t 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 exten ded along the entire length of the tape and reduced the difference bet ween the nominal cross section of the superconductor and its actual cu rrent-carrying cross section. At 77 K and self-field, a maximum J(c) o f 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 ave rage thickness of the superconducting layer between the sides of silve r layers was in the order of 1-2 mu m and the width was 3.6 mm. This s tudy confirms that the current-carrying region in BSCCO tapes is the l ayer adjacent to the Ag sheath. Previously it was shown that the super conductor core for thicker superconductor layers (similar to 70 mu m) does not carry significant current.