Raman study on Bi-Pb-Sr-Ca-Cu-O superconductor thin films grown by spray pyrolysis on several types of substrate

We present a Raman study on Bi-Pb-Sr-Ca-Cu-O thin films grown by spray pyrolysis on three different types of substrate, MgO, LaAlO₃ and SrTiO₃. We applied the technique of Raman difference spectroscopy to obtain a signal representing the spectrum from the Bi-Pb-Sr-Ca-Cu-O thin films, since the contribution of the Raman signal from the underlying substrate may overwhelm the scattering arising from the films. The films investigated were prepared by a two-step procedure, i.e. by the deposition of films on substrates from an aerosol of aqueous nitrate solution, followed by solid-state reaction at high temperature. The Raman spectra between 380 and 800 cm^-1 show a series of vibrational optical modes, all of them apparently superimposed on an electronic background. A Fano-type analysis was performed of the lineshape as a function of temperature for the most important modes, which can be associated with stabilization of the phase and related to the Cu-O plane, where superconductivity apparently originates.