High temperature resistivity and oxygen exchange kinetics in the Ba sub 2 YCu sub 3 O sub x superconductor.

The resistivity of Ba sub 2 YCu sub 3 O sub x was measured in the 450-850C range at various oxygen partial pressures. The tetragonal to orthorhombic phase transition is observed as a change in slope of the resistivity curve. The lack of discontinuity in the curve is consistent with the phase transition being higher than first order. It was found that decreasing the oxygen content, x, below 6.2 changed the resistivity of the tetragonal phase from metallic character to semiconducting character. In the metallic region of the tetragonal phase the superconducting transition temperature is depressed below 60K, while in the semiconducting region, no superconducting onset was observed down to 6K.