SILVER-DOPED (BI,PB)2SR2CA2CU3O10/AG HIGH-TEMPERATURE SUPERCONDUCTING COMPOSITES

The effect of silver doping on the microstructure and transport properties of Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3AgxO10 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.