Timothy J. Haugan, Winnie Wong-Ng

The lack of intrinsic flux-pinning centers in Bi₂Sr₂CaCu₂O_8+x (Bi-2212) high temperature superconductors (HTS) limits their usefulness for applications >20K. This paper will examine how to enhance the flux-pinning of practical Bi-2212 superconducting thick film tapes at temperatures >20K, by utilizing the phase equilibrium diagrams of Bi-2212 to produce and control a high density of (Sr,Ca)₁₄Cu₂₄O_41+y (14:24) secondary-phase needle-like defects that are in stable equilibrium with the Bi-2212 phase. Precursor powder compositions will be chosen and tested from phase equilibrium diagrams, to determine the optimal Bi:Sr:Ca:Cu starting compositions that result in only 2212 phase and 14:24 defects in precursor powders and melt-processed tapes. The size and density of 14:24 defects will be optimized for flux-pinning by adjusting melt process conditions and other process variables for each starting composition powder. Theory and related experiments predict that flux-pinning will increase ~V_f/d, where V_f is the volume fraction of defect, and d is the particle diameter. Experimental results of flux-pinning will be compared with this model.