Activities of copper in the Y--Ba--Cu--O system

The vapor pressures of Cu in equilibrium with YBa2Cu3O6.24 were measured as a function of temperature by the Knudsen effusion method using a quadrupole mass spectrometer as the detector. The data were fitted to ln [P(Cu)/bar]=(-66104±4485)(1/T)+(35.360±3.869). The activity of Cu [in YBa2Cu3O6.24(s) ] was calculated as the ratio of the above equilibrium pressure divided by the vapor pressure of pure Cu(s). From the activities, relative chemical potentials were calculated. The vapor pressure of Cu from the superconductor intersects the vapor pressure of Cu from pure Cu(s) at 1290±20 K, which indicates that the superconductor decomposes to metallic Cu at temperatures greater than 1290 K