Effect of the fluorine substitution for oxygen in the heavily Pb-doped Bi-2212 phase of (Bi, Pb)₂(Sr, Ba)₂CaCu₂O₈

Polycrystalline samples of the Bi-2212 phase of Bi2-x Pb x Sr2CaCu2O8-z F z with x(Pb) = 0.6 and 1.0 have been prepared. All the samples are almost of the single phase with the Bi-2212 structure for x(Pb) = 0.6. The value of Tc ∼ 82 K for z(F) = 0 increases up to 86-88 K for z(F) = 0.2-0.6. This may be due to the decrease in the amount of vacancy at the O-site by the introduction of F-. In addition, we have successfully synthesized the partially Ba-substituted Bi-2212 phase of Bi1.4Pb0.6Sr2-y Ba y CaCu2O7.8F0.2 with 0 ≤ y(Ba) ≤ 0.5. Tc increases up to 98 K for y(Ba) = 0.5. The enhancement of Tc through the Ba-substitution may be due to the increase in the distance between Cu and the apical oxygen.