Bulk YBCO samples obtained by the copptn. method show a const. and reproducible transition temp. of 92 ± 1 K together with a const. oxygen stoichiometry. The d. is approx. 90% of the theor. value and reflects a virtually pore depleted microstructure, consisting of closely interconnected twinned grains. Samples obtained from the solid state reaction of mech. mixed oxides have a d. 70-80% of the theor. value. The microstructure, even in optimum stoichiometry conditions, which are more difficult to obtain in a reproducible way, consists of large elongated twinned grains poorly interconnected. This pore dense structure is not homogeneous on a macroscale, showing locally domains of unwanted phases. The orthorhombic samples produced by copptn. are more stable. Measurements of the crit. current in progress, seem to indicate also a substantial increase of the current. [on SciFinder(R)] CAPLUS AN 1993:180984(Conference)