Investigation Of YBa₂Cu₃O_7-gd Films Grown on Vicinally-Polished MgO Substrates

Abstract

X-ray diffraction and transmission electron microscopy have been used to study the morphology and defect structure of YBa₂Cu₃O₇-δ films on {xc[001]} MgO substrates polished away from the {xc[001]} crystallographic axis towards either {xc[010]} or {xc[110]} by angles ranging from 1° to 20°. On the {xc[010]} off-axis substrates it was found that growth of the YBCO film was highly influenced by the surface normal of the substrate with only very weak alignment to the substrate {xc[001]} direction. All {xc[010]}-angled samples maintained T_cs's of 86K. Angles of 1°, 2.5°, and 5° toward {xc[010]} produced films with large mosaic spread parallel to the direction of the angle, as high as 4° FWHM for the 5° sample. Critical current densities of these films remained as high as those of films grown on on-axis substrates, e.g. 4.4x10⁷ A/cm² at 4.2 K and zero applied field. Larger off-axis angles led to samples with reduced mosaic spread but still alignment to the surface normal, and reduced Jcs's of 2x10⁷ A/cm² and 1xl0⁵ A/cm² for 10° and 20° angles, respectively. TEM investigation and in-plane x-ray examination of the 5°, 10°, and 20° samples show good in-plane texture except for the 20° sample, and increased granularity with angle. Films on substrates polished off-axis towards {xc[110]} have degraded T_cs's and J_cs's for all angles.