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

Abstract

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 (0–5 T) was analyzed. By using the resistivity data, the upper critical field and the coherence length at T = 0 K were deduced. For H⊥c , HC2(0) and ξ(0) values were calculated as 31, 31.3, 36.7, 38.3, 35.1 T and 33.1, 32.4, 30.0, 29.3, 30.6 Å, for 0.0, 0.05, 0.075, 0.10, and 0.15 Na-doped samples, respectively. For H ||c, HC2(0) and ξ(0) values were 95 and 112.3 T and 18.6 and 17.1 Å, 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 0.19 eV for 0 T and 0.06 eV for 5 T.