Oxygen diffusion in laser-ablated YBa2Cu3Ox thin films studied by spectroscopic ellipsometry

In the photon energy range of 2.1 to 4.6 eV and in the temperature range of 20 to 700oC, the complex dielectric function of oxygen deficient YBa2Cu3O6 has been measured and compared to that of YBa2Cu3Ox in an ambient of 1 bar of oxygen, using spectroscopic ellipsometry. It has been observed that the optical 4 eV transition, which is associated with oxygen deficiency, vanishes before the YBCO thin film is fully oxygenated. Oxygen diffusion coefficients have been estimated by real-time monitoring of the dielectric function during isothermal in-diffusion. It has been found that for T≥300oC oxygen can enter the YBCO thin film whereas for T=200oC, no oxygen in-diffusion has been observed. (orig.)