Dependence of crystalline orientation on film thickness of sputtered YBa₂Cu₃O _7-x on an MgO substrate

We have systematically investigated dependence of crystalline orientation on film thickness of sputtered YBa₂Cu₃O_7-x (YBCO) on an MgO substrate by the X-ray diffraction (XRD) method, the φ diffraction method and atomic force microscope (AFM). From examination of crystalline orientation by XRD method and in-plane orientation by the φ diffraction method, for thinner film below about 500 nm, the YBCO film is oriented with the c-axis perpendicular to the MgO substrate surface. For thicker film above about 500 nm, the c-axis oriented grains in the YBCO film vanish entirely and the a-axis oriented grains are formed. The rectangular images of a-axis oriented grains are also observed on the surface by AFM. We found that the crystalline orientation change drastically from c-axis oriented films to a-axis oriented films with increasing film thickness.