In situ preparation and transport properties of YBa₂Cu₃O₇ films on sapphire with Zr(Y)O₂ buffer layers

YBa₂Cu₃O₇ films on sapphire substrates prepared by laser ablation show c‐axis‐oriented growth and critical temperatures as high as T_c(R=0)=90 K. Due to diffusion processes and the formation of a nonsuperconducting intermediate layer the critical current density J_c is comparatively low. To overcome these difficulties the sapphire substrates were covered by Zr(Y)O₂ films acting as diffusion barriers. The preparation of these films was performed by laser ablation using a multitarget system. The structure and the surfaces of the films were characterized by x‐ray diffraction and scanning electron microscopy, respectively. The transport properties of the superconductor films are similar to those on suited substrates. Critical current densities up to J_c (77 K)=5×10⁵ A/cm² were achieved. In order to gain information about the pinning mechanisms measurements of the dependencies of J_c on the orientation between the crystal c axis and the external magnetic fields were carried out using samples with different buffer layer thicknesses. From the received data no indication of pinning by point defects in addition to the intrinsic planar pinning mechanism was detected.