Abstract
Samples with compositions of Bi:Pb:(Sr, Ba):Ca:Cu=0.9:0.2:(1.0-x, x):1.0:1.6, in which O≤x≤0.07, were prepared by heating at 844°C in air after heating at 828°C in air or at 787°C in Ar.The Pb-free(or poor)low-Tc phase with a tetragonal structure was formed by heating at 828°C in air, while the heat treatment at 787°C in Ar led to formation of the Pb-rich low-Tc phase with anorthorhombic structure. The lattice parameter c of these low-Tc phases increases as x increases, resulting from the Ba substitution for Sr. By the final heating in air, the high-Tc phase formsthrough the Pb-rich low-Tc phase as well as the Pb-poor one. Ba substitution promotes theformation of the high-Tc phase and elongates its c-axis length.
