Effects of the annealing conditions on the structural and superconducting properties of Bi2-xPbxSr2Y0.2Ca0.8Cu2Oz

The effects produced by the annealing in nitrogen atmosphere at relatively low temperatures (400-500°C) on the structural and superconducting properties of Bi2-xPbxSr2Y0.2Ca0.8Cu2Oz have been investigated. The electrical propertie s of the examined samples (0.0<=x<=0.4), which are comparable when prepared in air, vary remarkably for similar nitrogen annealing, depending on the lead content of the phase. The disappearance of the superconducting transition (reversible for retreatments in air) was found for x=0 whereas no appreciable variation of Tc was evidenced for x=0.4, at least for the applied treatments; an intermediate behavior was observed for the x=0.2 sample. The structural changes and the local modulated structure were observed by high-resolution electron microscopy. The effect of lead substitution in stabilizing Tc is discussed