The High-Tc Phase with Tc=117K in the Bi,Pb-Sr-Ca-Cu-O System

Samples with various compositions, (Bi_1-α Pb_α)_nSr_1.0Ca_1.0Cu_YO_X, where 0.16≤α≤0.36, n=l.l and 1.2, and 1.50≤Y<1.80, were heated in the temperature range from 840 to 860°C for 24 to 300h. Superconducting properties were studied by the measurements of the dc electrical resistivity as well as the ac magnetic susceptibility. Furthermore, lattice parameters were determined by the powder X-ray diffraction method. For the Pb-rich samples with α≥0.30 heated at 850°C for 120 to 192h, Tc(R=0) was found to be 116K and the Meissner effect was confirmed below 117K. The samples consist mainly of the high-Tc phase, although a small amount of Ca₂PbO₄ was observed. Tc(R=0) does not exceed 110K for α≤0.24, whereas the samples with α≥0.26 show Tc≥110K. n and Y seem to have no influence upon Tc(R=0). In comparison with the lattice parameters in the Pb-poor samples (α=0.18 and 0.20) with Tc(R=0)~107K, the c axis was found to be longer in the Pb-rich samples with α=0.34 and 0.36 showing Tc(R=0) around 115K, though the a axis was unchanged. The expansion of the c axis may result from an increase in Pb content substituted in the high-Tc phase.