Resonance Raman scattering as a probe of oxygen dynamics in YBa2Cu3Ox

We report on the metastable photo-bleaching of the 2.15 eV yellow Raman res onance in oxygen deficient YBa2Cu3Ox (x = 6.35-6.87), extending investigati ons by Wake ct al. (Phys. Rev. Lett., 1991,67, 3728) for x approximate to 7 . Polarization, x dependence and phonon spectra indicate that the resonance is localized at oxygen vacancies in long CuO-chains. The resonance is ther mally reactivated from the metastable bleached state with a relaxation time tau similar to exp[Delta/k(B)T] with Delta approximate to 1 eV. The result ing temperature dependent equilibrium resonance intensity essentially miner s the oxygen superstructure disordering around T* approximate to 100 degree s C observed in the same crystals by hard X-ray diffraction, thus offering a new effective probe of chain-oxygen dynamics in YBa2Cu3Ox. (C) 1998 Elsev ier Science Ltd. All rights reserved.