Thermopower and lattice parameters of YBa2Cu3O7-delta thin films as a function of oxygen content

The stoichiometry and structure of Y123 compounds strongly determine their physical properties. A theoretical and experimental study in oxygen-deficie nt YBa2Cu3O7-delta thin films is presented in this report. We have measured resistivity and thermopower in a set of high quality epitaxial samples wit h 0 < delta < 0.5. The c-axis lattice constant has been determined by X-ray spectroscopy. All lattice lengths have been evaluated numerically in the s ame range of composition using the microscopic effective medium theory. The calculated results compare well with those reported experimentally. A corr elation has been undertaken among the above and other physical quantities, in particular bond lengths, T-c, and the isotope effect, and some conclusio ns have been extracted. The main conclusion from the present work is that, although the electron-phonon interaction alone is not enough to explain the peculiarities of Y123 based compounds and its high T-c, phonons yield impo rtant contributions to their thermal transport properties.