We report in situ Raman spectra from single-crystal ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ in oxygen at temperatures from 20 to 770°C and from Y${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.2}$ in argon at temperatures from 20 to 545°C. For ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ in oxygen, a defect-induced phonon at ∼570 ${\mathrm{cm}}^{-1\mathrm{}}$ appears above ∼500°C and increases in intensity with increasing temperature and loss of oxygen. As Y${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.2}$ is heated above ∼100°C, dramatic changes occur in the phonon bands, resulting from a three-dimensional reorganization (disordering) of the oxygen in the structure involving the formation of oxygen vacancies at the O(4) sites.

• Received 14 April 1988

DOI:https://doi.org/10.1103/PhysRevB.38.2914