UNIVARIANT REACTIONS IN THE YBCO SYSTEM AND THE INFLUENCE OF OXYGEN ON SOLIDIFICATION AND MICROSTRUCTURE

Several aspects of the Y-Ba-Cu-O phase diagram have been investigated by thermal analysis, isopiestic, and soaking methods in various gas environments in more detail. On the basis of the univariant reactions at p(O-2)approximate to 0.21 x 10(5) Pa (especially e(1) and m(1)) and oxygen balance considerations, consequences concerning single crystal growth as well as texturing techniques have been derived. It is shown that oxygen diffusion through the melt can become an important technological factor. Phase diagram investigations at reduced oxygen partial pressure, especially the stability field of YBa2Cu3O7-delta and the pressure dependence of the e(1) reaction, give rise to modified techniques of melt processing at lower temperatures.