Preparation and Stability of Ba-Y-Cu Oxide Superconductors

The structural, electric and magnetic properties of samples in the Ba-Y-Cu oxide systems, fabricated by a conventional ceramic mixing technique, were investigated. Superconductors were obtained for compositions near Ba:Y:Cu=2:1:3 (atomic ratios) and in the sintering temperature range 850 to 1000°C. This composition and temperature range corresponds to conditions for the formation of Ba2YCU3O7-Y compound in this system. Superconducting samples were decomposed into BaCO3, BaY2CuO5 and CuO by the absorption of water. A sample which had been aged at room temperature for several tens of days exhibited a remarkable change in electrical resistivity, while showing only a slight change in its magnetization curve and X-ray diffraction pattern. This change may possibly be due to the absorption of water into grain boundaries. Similar changes were also observed in a sample aged at 200°C.