Effect of Ag addition on the electrical properties of (Bi2-xPbx)Sr2CaCu2O8+δ textured ceramics

Abstract

The development of commercial applications based on high temperature superconductors requires the use of texturing techniques in order to obtain the properties that are needed for technological applications. The Bi2Sr2CaCu2O8+δ (Bi-2212) superconductor has demonstrated its suitability for many applications when it is properly processed. A texturing technique for Bi-2212 bulk materials is the laser floating zone (LFZ) method. The superconducting materials textured by this technique, have very well aligned crystals, with their a-b planes parallel to the current flow. These textured bulk materials have very interesting properties that have been used to design current leads or fault current limiters which contribute to improve quality, reliability and flexibility of the electric grid. However, the low slope of the superconducting to normal transition on the electrical current curve, E-I, imposes limitations for their application as fault current limiters. A solution to overcome this problem is based on the cationic substitution, which could introduce effective flux pinning centres and increase the slope of the E-I curves. Previous works, on the Bi substitution by Pb has demonstrated that the slope of the I-V curves can be increased considerably. On the other hand, small Ag additions have shown to be very useful in order to improve considerably the mechanical behaviour of these totally melt-processed materials. In this work we analyse the influence of simultaneous additions (Pb and Ag) on the microstructure and the superconducting properties of LFZ textured (Bi2-xPbx)Sr2CaCu2O8+δ bars, with x = 0 and 0.4 and small (0,1 and 3% wt) Ag additions.