SUPERCONDUCTIVITY OF BI-2201 (N = 1) AS INFLUENCED BY THE SUBSTITUTION OF PB AND OR RARE-EARTHS (R = LA, ND AND PR)

Preparation conditions for stabilizing the bulk superconductivity (T(c) = 9.5 K) in the nominal Bi2Sr2CuO(approximately 6) composition corresponding to the n = 1 phase in the Bi2Sr2Ca(n-1)Cu(n)O2n+4 system are described. The samples Bi2.1Sr1.9CuO(y) and Bi2.2Sr1.8CuO(y) become superconducting at 10 K and 12 K, respectively. Single-phase compounds (space group Amaa) could be synthesized for the range 0 less-than-or-equal-to x less-than-or-equal-to 1.0 in the series Bi2Sr(2-x)La(x)CuO6+y but the orthorhombicity decreased gradually with increase in x and the structure became tetragonal at x = 1.0. The T(c)(R = 0) value increased to a maximum of 19 K for x = 0.4, corresponding to a value of approximately 2.2 for the formal valence of copper. For x greater-than-or-equal-to 0.5 a sudden loss of superconductivity is observed. Simultaneous substitution of Pb for Bi, and, La for Sr yields further improvement in superconducting characteristics, hitting a peak of 26 K (R = 0) for x = 0.4 in the series Bi(2-x)Pb(x)Sr(2-x)RxCuO(y) (R = La). The R = Nd- and and Pr-substituting compounds showed lower values of T(c) for the same extent of doping (x = 0.4). Interestingly, doping of Pb alone (i.e., Bi(2-x)Pb(x)Sr2CuO(y)) results in suppression of superconductivity altogether. The electrical resistivity, magnetic susceptibility and the cell parameter data are presented for varying levels of different substituents and discussed.