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

Abstract

Microstructural properties and their influence on Jc have been studied in detail on Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox tapes prepared by the powder-in-tube method. The present study centres on two important factors for the achievement of high Jc values: (1) The liquid phase reaction during the (2223) phase formation at 847 degrees C for the composition Bi1.72Pb0.34Sr1.83Ca1.97Cu3.13Ox leads to better connectivity between the (2223) platelets, thus considerably improving Jc (77 K, 0 T): single phase (2223) packing powders formed no liquid during the heat treatment and therefore reached Jc values of only up to 1*104 A cm-2 while multiphase calcined packing powders showed higher Jc values, of 2.6*104 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 Jc up to 3.3*104 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 Jc values in the oxide layer up to 60 mu m thickness with a regular shape of the cross section.