We have recently found several metamorphic phases of Ba2YCu3O9-δ. In addition to the high T c orthorhombic phase, two tetragonal and another orthorhombic phases of them were studied with X-ray diffraction, susceptibility and resistivity measurements. We found that the high T c phase is a weak Pauli paramagnet and one of the tetragonal phases is a magnetic semiconductor with a phase transition around 8 K. The results are briefly discussed in relevance to the superconductivity in this series of oxides.
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Nakazawa et al. (1987) studied this question.