MICROSTRUCTURAL STUDY OF BI(2223)/AG TAPES WITH JC(77-K, 0 T) VALUES OF UP TO 3.3X10(4)A CM-2

Microstructural properties and their influence on J(c) have been studied in detail on Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3O(x) tapes prepared by the power-in-tube method. The present study centres on two important factors for the achievement of high J(c) values: (1) The liquid phase reaction during the (2223) phase formation at 847-degrees-C for the composition Bi1.72Pb0.34Sr1.83Ca1.97Cu3.13O(x) leads to better connectivity between the (2223) platelets, thus considerably improving J(c) (77 K, 0 T): single phase (2223) packing powders formed no liquid during the heat treatment and therefore reached J(c) values of only up to 1 x 10(4) A cm-2 while multiphase calcined packing powders showed higher J(c) values, of 2.6 x 10(4) A cm-2. (2) The degree of texturing of the a-b planes in the (2223) platelets varies throughout the oxide layer. The highest degree is found at the Ag/(2223) interface. It gradually decreases towards the centre of the oxide layer. Mixing of Ag powders with the packing powders enhanced J(c) up to 3.3 x 10(4) A cm-2, due either to the enhanced interface area or to the prevention of cracks during the cooling process. The effect of the powder packing density was also studied: higher packing density (80%) was found to lead to higher J(c) values in the oxide layer up to 60-mu-m thickness with a regular shape of the cross section.