The Effect of Pb Addition on Superconductivity in Bi-Sr-Ca-Cu-O

The effect of Pb addition on superconductivity was studied on the systems with nominal compositions (BiPb x ) 2 Sr 2 Ca 2 Cu 3 O y , (Bi 1- x Pb x ) 2 Sr 2 Ca 2 Cu 3 O y and (Bi 1- x Pb x ) 2 Sr 2 Ca 2 Cu 3.6 O y . The melting point decreases monotonically from ∼880 to ∼860°C as x increases from 0 to 0.45 in the systems, while the volume fraction of the high- T c phase (HTP) and the offset value of T c show a peak around x =0.2∼0.3. Further increase in x produces the Ca 2 PbO 4 , leading to the suppression of the HTP. The amount of Pb suitable for the formation of the HTP is limited by the competition between the reaction to form the HTP by the catalytic effect of Pb and the one to form the Ca 2 PbO 4 .