STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF BI2-XPBXSR2CACU2O8+DELTA

Substitution of Pb for Bi in polycrystalline Bi2-xPb(x)Sr2CaCu2O8+delta has been achieved up to the solubility limit of x = 0.35 +/- 0.03 for two annealing temperatures, 800-degrees-C and 820-degrees-C. Further addition of Pb beyond the solubility limit leads to a decrease of the Sr-concentration from 2.0 to 1.8 atoms per formula unit. The microstructure of the samples and the chemical composition of all phases present have been studied by scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (EDX) and electron probe microanalysis (EPMA). The decrease of T(c) from 85 K to 76 K for x = 0 to x = 0.35 can be explained in terms of increasing hole concentration in a hole-overdoped regime. A micro-Raman scattering investigation corroborates the substitution of Bi3+ by Pb2+: whereas the frequency of the "in-phase out-of-plane" vibration of the oxygen atoms situated in the CuO2-planes is not affected by the Pb-substitution, the frequency of the vibration of the oxygen atoms in the BiO-layers scales with T(c). The frequency of the "bridging oxygen" reflects also the substitution of Bi3+ by Pb2+ and the decrease of the a- and b-axes up to the solubility limit.