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

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Abstract
YBa2Cu3O7films 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)O2films 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.