Microstructural study of Bi(2223)/Ag tapes with Jc(77 K, 0 T) values of up to 3.3*10⁴A cm⁻²

Microstructural properties and their influence on J c have been studied in detail on Ag-sheathed (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x tapes prepared by the powder-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 Bi 1.72 Pb 0.34 Sr 1.83 Ca 1.97 Cu 3.13 O 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*10 4 A cm -2 while multiphase calcined packing powders showed higher J c values, of 2.6*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*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.