High-temperature resistance of YBa₂Cu₃O_7-δ films under various oxygen pressures

The electrical resistance of a c-axis-oriented YBa₂Cu₃O_7-δ film is measured at elevated temperatures, under various values of oxygen pressure. The resistance shows a monotonic increase with substrate temperature up to around 450 °C, indicating little oxygen out-diffusion. Above this temperature, the rapid increase of the electrical resistance shows out-diffusion of oxygen from the film. As the temperature is increased, an abrupt drop occurs above a certain temperature (T_m) where the resistance indicates its highest value. T_m has an oxygen pressure dependence, which is similar to the oxygen pressure dependence of the orthorhombic-to-tetragonal transition line in an oxygen pressure-inverse of temperature phase diagram of YBa₂Cu₃O_7-δ. From the observation of surface morphologies, the T_m is thought to be a sort of melting temperature where a partial melting of the YBa₂Cu₃O_7-δ film occurs.