Formation of the Pb-rich 2212 Phase

Abstract

The Pb-substitution effects on crystal structure and Tc were examined in samples of Bi-2212 phase with a composition of Bi_4-xPb_xSr₃Ca₃Cu₄O_z(O≤x≤2.2). The crystalline symmetry of the Pbsubstituted 2212 phase depends upon Pb-composition: tetragonal(x≤0.4), orthorhombic(A)(0.6≤x≤1.4) and (B)(1.6≤x≤2.0). It is noteworthy that a considerable portion of Pb maybe located at the Sr site besides the Bi site in orthorhombic(B) while Pb occupies the Bi site in orthorhombic(A). Thermal behavior of Pb-substituted 2212 phase was also studied by characterizing samples annealed at 400°C in air and subsequently reheated at 800°C in Ar. Interesting precipitation and dissolution on reactions were found.