Silver-doped (Bi,Pb) 2Sr 2Ca 2Cu 3O 10/Ag high-temperature superconducting composites

Abstract

The effect of silver doping on the microstructure and transport properties of Ag-sheated (Bi,Pb) 2Sr 2Ca 2Cu 3Ag x O 10 composite tapes has been investigated through scanning electron microscope (SEM) observation and electrical measurements including critical temperature ( T c), critical current density ( J c) and J c behaviour in magnetic field for a series of samples with varying dopant levels ( x = 0.0–3.5). The results show that silver doping has no noticeable effect on the T c of the samples, but influences the sample's J c, which decreases with increasing silver doping content when the samples are sintered at the same temperature. A slight improvement of J c behaviour in magnetic field is observed for the lightly doped samples, while higher-level doping shows a small degradation in the J c behaviour. Microstructural analyses reveal that silver exists as an isolated phase inside the tapes without visible reaction with and diffusion within the superconductor matrix, so has no influence on T c. But the undesirable shape and size of the silver particles cause grain misorientation, and hence lead to a decrease in J c. The influence of silver doping on the J c behaviour in magnetic field is a combined effect of grain alignment, grain conductivity and flux pinning.