Phase diagram and new phases in the Y-Ba-Cu-O system at high oxygen pressure

Chandrachood, M. R. ; Morris, D. E. ; Sinha, A. P. B. (1990) Phase diagram and new phases in the Y-Ba-Cu-O system at high oxygen pressure Physica C: Superconductivity, 171 (1-2). pp. 187-193. ISSN 0921-4534

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Official URL: http://www.sciencedirect.com/science/article/pii/0...

Related URL: http://dx.doi.org/10.1016/0921-4534(90)90473-R

Abstract

The Y-Ba-Cu-O phase diagram has been determined at 980° C at high oxygen pressure 200 bar=20 mPa. It shows several differences from the phase diagram at 1 bar. Highly oxidized phases are stabilized: BaO2 instead of BaO and YBa2Cu4O8 instead of YBa2Cu3O7-x. Two new phases have been observed: YBa5Cu2O10-x has a tetragonal unit cell with a=5.88 Å and c=8.04 Å , consistent with a four layered structure such as CuO2-BaO-(½ Y + ½ Ba)O-BaO, while YBa2Cu2O6-x appears to be isomorphous with the superconductor La1.6Sr0.4CaCu2O6. In addition, we find a high-pressure BaCuOx phase, its X-ray diffraction (XRD) pattern indicates a perovskite related layered structure which has a unit cell a=5.68 Å , c=14.40 Å . The formation of compounds on the YO1.5-BaO line: Y2Ba2O5, Y2BaO4 and Y2Ba4O7 is suppressed at high P(O2). Tie lines are observed to join CuO-2:1:1, 2:0:2-2:1:1, YO1.5−2:1:1, 2:1:1-BaO2, CuO-1:2:4 and 2:1:1-1:2:4.

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