Raman study of the oxygen vibrations in 123-superconductors

Abstract

A systematic study of the characteristic Raman active phonons due to the vibrations of the oxygen atoms (out-of-phase, in-phase of O2,3 and apex) has been carried out in the YBa2Cu3O6 + x superconductor, with varying and very well defined amount of oxygen and with site selective substitution by 18O. The anharmonic behaviour of the three oxygen modes is examined as a function of the oxygen concentration and compared with previously published work. The association of the new modes which appear at low doping with the oxygen vibrations is delineated by the isotopic substitution. From the evolution of the spectral characteristics with oxygen content, the existence of other phases is investigated. Finally, a novel characteristic which appears in the spectra beyond optimum doping is discussed.