The Y-Ba-Cu phase diagram was extrapolated from the binary subsystems.
The Y-Ba miscibility gap was estimated from the shape of the ternary
miscibility gap near the Cu corner. The calculated phase diagram is in
good agreement with the differential thermal analysis and X-ray exper
imental results. An application of the phase diagram to potential proc
essing routes of a metallic ''YBa2Cu3'' precursor is given.