抄録
The compound Ba2YCu3O7-y with various 7-y was annealed in sealed gold and silica capules at 350-570°C and 0.1 MPa. Linear depression of the superconducting transition temperature(Tc) occurred with a decreasing 7-y, and Tc was zero at 7-y= 6.40 -6.45. Tetragonal phase with 6.4>7-y>6.34 was unstable below 570°C. Superstructure due to regular arrangement of oxygen vacancies was observed at 7-y=6.48. The specimen was reactive with moisture, and became a non-superconductor, although the structure remained unchanged. Coexistence of tetragonal and orthorhombic phases was observed in a specimen with 7-y=- 6.47.
