New compositions of the high-${\mathit{T}}_{\mathit{c}}$ superconductor ${\mathrm{YBa}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Bi}}_{\mathit{x}}$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, with x≤0.5, have been prepared by the usual ceramic process. The presence of bismuth (x<0.3) in these compositions activates crystallization of the superconductor phase (which gives an improved ${\mathit{T}}_{\mathit{c}}$∼97 K), processed at 930 °C/12 h in an ${\mathrm{O}}_2$ atmosphere. The crystallites exhibit very small sizes and sharp distribution.

• Received 9 July 1990

DOI:https://doi.org/10.1103/PhysRevB.42.8627