In-plane texturing and its effect on critical current densities of YBa₂Cu₃O_7-x thin films grown on polycrystalline substrates

It is demonstrated that on polycrystalline substrates, a-b plane textures of c-axis oriented YBa₂Cu₃O_7-x (YBCO) thin films can be controlled with biaxially aligned yttria-stabilized zirconia (YSZ) buffer layers grown by ion beam-assisted pulsed laser deposition. An X-ray φ scan measurement shows that the in-plane alignment of the a- (or b-) axes in polycrystalline YBCO thin film is determined by the in-plane texture of YSZ buffer layer. The transport critical current density (J_c) of the YBCO thin film was found to directly correlate with its degree of in-plane alignment characterized by the full-width at half-maximum (FWHM) of YBCO (103)/(013) φ scan profile. For a YBCO thin film with the FWHM of 27°, J_c shows an order of magnitude increase in comparison to YBCO thin films with a random in-plane distribution of a- and b-axes. Using a numerical method to describe the distribution of the a- (or b-) axes of YBCO grains, the misorientation angles of the grain boundaries were determined, and the transport critical current densities of polycrystalline YBCO thin films were calculated. The results are in good agreement with the experimental J_c data for samples with different degrees of in-plane alignment. It indicates that the reduction of the number of high-angle grain boundaries is the main reason for the improved J_c observed in the biaxially aligned YBCO thin films.