THERMODYNAMIC AND KINETIC EFFECTS OF LEAD DOPING ON THE FORMATION OF (BI,PB)(2)SR2CA2CU3OY

Lead doping affects the thermodynamics and kinetics of the formation o f (Bi,Pb)(2)Sr2Ca2Cu3Oy. Although neither the enthalpy change nor the entropy change of the reactions can be predicted quantitatively, it is shown that the escape of volatile PbO and O-2 from the open thermodyn amic system is of crucial importance for the complete conversion of al l impurities. Besides, the accelerated diffusion of the reactants in t he lead rich partial melt ''L'' as well as the structural stabilizatio n due to incorporation of Pb2+ on bismuth sites are essential factors facilitating the formation of the 2223 phase. Only the interplay of al l the three effects leads to the complete formation of the superconduc ting 110 K phase in an open system.