ANNEALING TEMPERATURE-DEPENDENCE OF MGO SUBSTRATES ON THE QUALITY OF YBA2CU3OX FILMS PREPARED BY PULSED-LASER ABLATION

The effect of annealing on a MgO substrate was systematically investigated, varying the annealing temperature, for preparation of high-quality YBa2Cu3Ox (YBCO) films by pulsed laser ablation. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were carried out for characterization of the MgO substrate and X-ray diffraction (XRD) measurement, including theta-2 theta scan, omega-scan (rocking curve) and phi-scan, and electrical measurement were carried out for characterization of YBCO films. Thermal annealing of MgO above 1000 degrees C in oxygen ambient was found to give rise to a great improvement of the crystallinity and the reproducibility of crystal orientation of YBCO films, while it was also found to induce Ca segregation on the surface of MgO and reduce the oxygen content of YBCO films. Annealing below 1000 degrees C causes no outstanding improvement in the crystal structure of YBCO. On the MgO substrate annealed at 1200 degrees C c-axis-oriented YBCO film was found to reproducibly show a full width at half-maximum (FWHM) of the rocking curve of 0.3 degrees, an FWHM of (005) diffraction of 0.1 degrees, an epitaxial relation without in-plane misorientation, a critical zero temperature of 89 K, and a critical current density of 10(6) A/cm(2) at 77.4 K and zero field.