Epitaxial growth of La₂Zr₂O₇ thin films on rolled Ni-substrates by sol-gel process for high T_c superconducting tapes

A solution process was used to grow epitaxial La₂Zr₂O₇ (LZO) buffer layers on roll-textured Ni (100) substrates to produce YBa₂Cu₃O_7-δ (YBCO)-coated conductors. The LZO precursor solution was prepared by an all alkoxide sol-gel route using mixed metal methoxyethoxides in 2-methoxyethanol. The partially hydrolyzed solution was either spin-coated or dip-coated onto the textured Ni substrates. The amorphous thin film was then heat treated at 1150 °C under (96%)Ar/(4%)H₂ atmosphere for 1 h. X-ray diffraction (XRD) of the buffer layer indicated a strong c-axis orientation on the Ni (100) substrate. The LZO (222) pole figure revealed a single cube-on-cube texture. SEM images of the LZO buffer layer showed a dense microstructure without cracks. The YBCO deposited on the sol-gel LZO-buffered Ni substrates with sputtered YSZ and CeO₂ top layers had a critical current density of 480,000 A/cm² at 77 K and self-field.