PHASE COMPATIBILITIES IN THE SYSTEM Y2O3- BaO - CuO

Phase relationships in the Y{sub 2}O{sub 3}-BaO-CuO system are reported at temperatures from 850{degree}C to 1100{degree}C. The compatibilities surrounding the superconducting Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub x} compound are summarized and discussed in the context of the existing literature. The recently discovered Y{sub 1}Ba{sub 3}Cu{sub 2}O{sub x} compound shows three possible structural types, related to the partial pressure of oxygen during fabrication. A new phase, the di-barium cuprate (Ba{sub 2}Cu{sub 1}O{sub 3}) has been isolated. It has a K{sub 2}NiF{sub 4}-type structure and is highly hygroscopic. Small additions of yttrium will convert the structure to a perovskite which serves as the end-member to an apparent solid solution region extending to Y{sub 1}Ba{sub 3}Cu{sub 2}O{sub x}. Low levels of lithium addition to the Ba{sub 2}Cu{sub 1}O{sub 3} can also convert its K{sub 2}NiF{sub 4}-type structure to a similar perovskite. This sensitivity to doping underscores the need for using pure materials in phase compatibility determinations.