ENHANCEMENT OF TC(ON), APPEARANCE OF A NEW PHASE AND FASTER KINETICS IN PB + SB DOPED BI2SR2CA2CU3OY

In an attempt to increase the volume fraction of the high T(c) phase Bi2Sr2Ca2Cu3O(Y)(2223), mixed doping of Pb + Sb was performed in a Bi superconducting system. A stoichiometric starting composition with Bi partially replaced by Sb + Pb was found to result in a system with an unusually high value (greater-than-or-equal-to 140 K) of onset transition temperature (T(c)on). A T(c)o of 111 K could be achieved with about 75 to 80% 2223 content, as calculated from the XRD data, for annealing duration of about 100 h, which is much less than in an undoped or Pb-doped Bi system. The most important characteristic of this system is the presence of a 'new phase' with its strong and sharp reflections near 2-theta = 30-degrees in the XRD pattern. Such a phase could never be detected in the Bi system doped only with Pb. Interestingly, the 'new phase' is found to be present even in the calcined material and its existence has been shown at all stages of annealing. R-T characteristics and XRD analysis have revealed the development of the low T(c) phase Bi2Sr2Ca1Cu2O(Y) (2212) at a very early stage of annealing, and further the transformation of 2212 into 2223, always in coexistence with the 'new phase' and CuO. Incorporation of Sb resulting in the formation of the 'new phase' appears to be responsible for T(c)on values that are usually high and also for making the kinetics of the solid state reaction of 2223 formation much faster.