Decomposition of YBa₂Cu₃O_7−x during annealing in CO₂/O₂ mixtures

The stability of YBa₂Cu₃O_7−x superconductors toward reactions with CO₂ in CO₂/O₂ gas mixtures has been studied during annealing at temperatures ranging from 600°C to 950°C. The results show that there are three different types of the reactions. The reaction products of these reactions all include BaCO₃ and CuO, while the third product is dependent on the annealing temperature. At 600°C, YBa-carbonates were formed while Y₂Cu₂O₅ and Y₂BaCuO₅ were formed at 815°C and 950°C, respectively. Transmission Electron Microscopy images show that the reactions started at grain boundaries with the formation of island-type precipitates.