MAGNETISM OF PR IONS AND SUPERCONDUCTIVITY IN BI2-XPBXSR2-XPRXCUO6+DELTA

Superconductivity is observed in Bi2-xPbxSr2-xRxCuO6+delta (Bi-2201) s amples for R = La, Pr and Nd and x = 0.1-0.4 under suitable preparatio n conditions. The maximum T(c) of 26 K is found for x = 0.4 in the La series, while for corresponding compositions in the Pr and Nd series, it is 21 K. Magnetic susceptibility measurements on Pr-containing Bi-2 201 samples reveal that the effective paramagnetic moment of the Pr io n is nearly the same in samples with different T(c) and has a value cl ose to that of free Pr3+ ion. This is in contrast to the situation in RBa2Cu3O7-delta series in which PrBa2Cu3O7-delta is non superconductin g and exhibits a Pr moment intermediate between that of Pr3+ and Pr4+. Thus the influence of the magnetism of the Pr ion, if any, on the T(c ) of Bi-2201 series appears to be small.