Fabrication and characterization of a-axis c-axis oriented YBa2Cu3Oy bilayer thin film

We have investigated YBa2Cu3Oy bilayer thin films consisting of different crystal-axis orientations. A c-axis oriented bottom layer is deposited on a SrTiO3 (100) substrate by pulsed-laser deposition, and then an alpha-axis oriented top layer is deposited by off-axis RF magnetron sputtering after reduction of the bottom layer. This reduction process contributes to the growth of the alpha-axis layer. At the interface between these layers, however, pyramidal c-axis oriented grains are observed. The alpha-axis oriented grains tilt by 2 degrees from the [010] and [001] azimuths of the substrate. This structure is suitable for good lattice matching between the a-axis grains and the pyramidal c-axis grains. This bilayer film exhibits good electrical properties having T-c = 80 K and J(c) = 2 x 10(6) A/cm(2) at 60 K. It is considered that the tilted structure of the alpha-axis oriented grains contributes to the superconductivity.