In-situ processing and reaction of CO2Cu3O7-x

This paper reports on heating YBa2Cu3O7-x up to 925 K which shows that CO2 and H2O are the major volatile impurities contained in this material as measured by Temperature Programmed Desorption (TPD). The level of these impurities can be reduced significantly by repeated annealing of the samples in oxygen (100 Torr, 673 K). In-situ resistivity measurements show the samples to be superconducting and as the impurity levels are decreased, the superconducting transition sharpens; however, no change in Tc is observed. TPD was also used to monitor the out-diffusion of O2, which occurred with an activation energy of 1.8 eV. Both oxidized (YBa2Cu3O6.9) and reduced (YBa2Cu3O6.5) forms of the material were exposed to CO2 at mild temperatures (325-725 K). TPD measurements show that the latter absorbs significantly more CO2. Indirect evidence by TPD suggests that a CO2 may insert into oxygen vacancies in the partially reduced material. Furthermore, the absorption of CO2 impedes the kinetics of subsequent oxygen uptake in this temperature range