IR absorption peaks and oxygen vacancies in YBa2Cu3Ox

Three absorption peaks (620 to 640, 590, 550 to 580 cm-1) are observed in the IR spectra of YBa2Cu3Ox. The variation of intensity and frequency of these peaks with annealing temperature and oxygen content is investigated. The nature of IR peaks is studied and assignment to various Cu-O bond-stretching vibrations is made and supported by the correspondence between peak frequency and appropriate Cu-O bond-length. Based upon the correlation between peak intensity and oxygen content, these peaks are further interpreted as 'quasilocalized' vibration mode of the Cu-O bond induced by the oxygen-vacancy in the one-dimensional Cu-O chain and two-dimensional Cu-O network. The corresponding vacancy formation energy is found to be 0.34 and 0.93 eV, respectively. These peaks may serve as an useful indicator of oxygen content, crystal structure, superconducting properties of YBa2Cu3Ox. (author)