Raman line shapes from sputtered thin films of Y(Pr)Ba2Cu3O6+delta: Fine structures and oxygen ordering

A temperature dependence study of Raman line shapes taken from superconducting and insulating Y(Pr)Ba2Cu3O6+delta thin films with well-characterized electrophysical properties and morphologies (a-axis or c-axis orientation) has been carried out using the excitation energies at 1.83 eV and 2.41 eV. Ba and Cu bands show doublers, with 113-119 cm(-1) and 146-152 cm(-1) components and have been calculated using a Green's function model. The shapes of the 113 and 152 cm(-1) lines are well described by Lorentzians whereas those of the other two components can be satisfactorily reproduced in the assumption that two phonons of bare frequencies 119 and 146 cm(-1) interact with a common continuum of excitations. The temperature dependence of the phonon-continuum coupling parameters allows us to ascribe the scattering continuum to low-energy electronic interband transitions. The model is able to explain qualitatively the overestimated mixing between pure Ba and plane Cu A(g) vibrational modes found in previous first-principles calculations. We also find that for the 1.83 eV exciting line, the B-1g oxygen phonon at 335 cm(-1) presents a strong Fano effect and anomalous temperature dependence. We link Raman features occuring at approximate to 220-240, 270-290, and 560-596 cm(-1) to the existence of local variations in oxygen composition resulting from the conditions of deposition. These lines could originate from chain defects and be activated by a coupling between A(g) and B-2g-B-3g modes. The presence of microphases of oxygen-depleted domains (ortho-II phase) reproducing macroscopic oxygen disorder is proposed.