Phase Relations in the Bi–Sr–Ca–Cu–M–O (M = Y, Dy, Ho, Er, Tm, Yb, Lu) Systems

The phase relations in the Bi–Sr–Ca–Cu–M–O (M = Y, Dy, Ho, Er, Tm, Yb, Lu) systems near Bi2Sr2CaCu2O8+ x(Bi-2212) were studied between 850 and 990°C. The results demonstrate that larger sized rare earths (Y, Dy, Ho, Er) substitute on the Ca site in Bi-2212, leading to the formation of CaO. Smaller sized rare earths (Tm, Yb, Lu) replace lesser amounts of Ca and form Sr2MBiO6phases. In the material of nominal composition Bi2Sr2Ca0.85M0.15Cu2O8 + x+ 0.25Sr2YBiO6prepared via melt processing, a major fraction of the Y atoms substitute for Ca in Bi-2212, resulting in a low-Tcmultiphase superconductor. In the analogous Yb system, a Bi-2212–Sr2YbBiO6composite with Tc= 87 K is obtained.