Control of the in-plane alignment and the critical current of polycrystalline YBa₂Cu₃O_{7 - x} thin films

Biaxially aligned yttria-stabilized-zirconia (YSZ) buffer layers are prepared on polycrystalline substrates using ion-beam-assisted laser deposition. The effect of directional ion bombardment on in-plane texruring of YSZ layer is investigated by four-circle X-ray diffractometer. Without the assisting ion beam, uniaxially aligned YSZ layers are obtained at room temperature, exhibiting a preferred orientation of the grains with the [001] axis perpendicular to the substrate surface. With the assisting ion beam, the in-plane texture of YSZ layer is altered as the (110) plane tends to align in the direction of the incident ion beam. The X-ray φ scan of (111) poles shows that the in-plane alignment of the YSZ layer improves as the ion beam voltage increases in the range 200-450 V. The improvement of YSZ in plane alignment is also observed as the layer thickness increases. On the biaxially aligned YSZ buffer layers, superconducting YBa₂Cu₃O_{7 - x} thin films are prepared and their transport critical current densities are found to be directly related to the in-plane alignment of the YBCO thin films. Using a numerical method to model the thin film as a matrix of two dimensional grains, a correlation is established between the line shape of X-ray φ scan and the measured critical current density of polycrystalline YBa₂Cu₃O_{7 - x} thin film.