Fabrication and optimization of Bi-2212 high temperature superconductors with K and Ag co-incorporation

Abstract

Polycrystalline bulks Bi2.1Sr1.96CaKxCu2.0O8+δ + yAg (Bi-2212) with different K incorporation content of x = 0, 0.02, 0.05 and 0.10 and addition of Ag nanoparticles with weight ratio of y = 0.10 wt% were fabricated by a hot-pressing (HP) process. The influences of K+ ions and Ag nanoparticles on the lattice parameters, phase composition, microstructures and related superconducting properties were systematically investigated. The introductions of K+ and Ag both obviously affected the thermodynamic parameters of Bi-2212 system. Accordingly the sintering temperature during HP process changed dramatically. After the HP process, increases of average grain size were obtained with Ag incorporation, based on both XRD and SEM analysis, which implied the formation of better texture alignment structure. Slight decrease of critical temperature was observed corresponding to the changing valence of Cu2+ ions on superconducting layer. Increase of superconducting phase volume was achieved on the K and Ag co-incorporated bulk. And the enhancement of current capacity was also achieved on the very same sample, under the magnetic field higher than 1 T. The different flux pinning mechanism between K and K/Ag incorporated sample from point pinning to surface pinning could be related to the microstructure change, which can be recognized as a solid evidence for the different effects of K and Ag.