Liquidus relations in Y--Ba--Cu oxides

The liquidus relations in the system YO/sub 1.5/--BaO--CuO/sub x/ in air in the compositional region near the superconducting oxide YBa2Cu3O/sub x/ were studied by differential thermal analysis, x-ray diffraction, electron microprobe analysis, and visual observation. The temperatures of 11 invariant points and the corresponding reactions were determined. YBa2Cu3O/sub x/ was found to melt incongruently at 1015 0C to Y2BaCuO5, which in turn melts incongruently to Y2O3 at 1270 0C. These reactions mean that preparing the superconducting phase by melting and rapid cooling will result in the presence of these two phases as well. The peritectic reaction YBa2Cu3O/sub x/+CuO→Y2BaCuO5+liquid at 940 0C accounts for the observation of partial melting, improved synthesis purity, and grain growth at temperatures of 950 0C. The determination of these invariant temperatures and reactions provide insight into optimal processing conditions