Some Aspects of the Nonstoichiometric and Thermodynamic Behavior of the YBa₂Cu₃O_z System

Abstract

The nonstoichiometric and thermodynamic behavior of the YBa2Cu3Ox system as a function of oxygen partial pressure and temperature is being investigated by means of a coulometric titration technique. The oxygen content of the superconductor can be varied coulometrically by well-defined small amounts and the equilibrium partial pressures determined from the EMF. The oxygen stoichiometry in YBa2Cu3Ox as a function of oxygen partial pressure shows a change of curvature around x = 6.55–6.75 and an inflection around x ≅ 6.65 at temperatures between 400–500°C. These new low temperature data are consistent with the presence of a miscibility gap at lower temperatures, which is similar to that postulated in several theoretical papers.

Photoinduced changes in high temperature superconducting films

“…Several Po,-T phase diagrams have been published . For reasons to be discussed elsewhere [20] we adopted for the present work the Po2-T phase diagram reported in [19]. The film is placed in a small stoi; chiometric YBCO ceramic box which in turn is placed inside a quartz tube and evacuated to P = 10-6Torr at room temperature.…”