Effect of Na-substitution on magnetoresistance and flux pinning energy of Bi-2212 ceramics prepared via hot-forging process

In this study, polymerization method with polyethyleneimine, followed by hot-forging process was used to synthesize bulk textured Bi2Sr2Ca1-xNaxCu2Oy (x=0.0, 0.05, 0.075 0.1, and 0.15) ceramics. Magnetoresistance performance of samples was studied by change of flux pinning mechanism. The effect of Na-substitution on the magnetoresistance, flux pinning energy, irreversibility field, upper critical magnetic field and coherence length was evaluated in the framework of thermally activated flux flow model. A resistivity transition broadening under various magnetic fields (0-5T) was analyzed. By using the resistivity data, the upper critical field and the coherence length at T=0K were deduced. For H-C2(0) and (0) values were 95 and 112.3T and 18.6 and 17.1 angstrom, for the samples of Na0 and Na2, respectively. In particular, the flux pinning or activation energies of Bi2Sr2Ca1-xNaxCu2O8+y where x=0.10 were determined to be 0.19eV for 0T and 0.06eV for 5T.