Effect of temperature and film thickness on microstructure and residual stress for YbBCO-coated conductors

The rare-earth mixed oxide (Gd_1-xHo_x)₂O₃ and the superconductor YbBa₂Cu₃O_7-x were prepared by sol-gel synthesis using metal-organic precursors. Textured Gd_1.802Ho_0.198O₃ buffer layers were grown on biaxially textured Ni (1 0 0) substrates. YbBa₂Cu₃O_7-x layers were epitaxially grown on the Gd_1.802Ho_0.198O₃-coated Ni substrates using the reel-to-reel sol-gel dip coating system. Different thicknesses of superconducting layers, annealed at various temperatures, were tried to observe the effects of thickness and temperature on residual stress and microstructure properties. Residual stress in the YbBCO/Gd_1.802Ho_0.198O₃/Ni was calculated analytically. The results showed that variation of residual stress along the thickness of structure (Ni substrate, buffer layer and YbBCO film) was constant. We also observed that the Ni substrate is under tension while buffer layer was under compression in the case of without YbBCO layer. However the residual stress was under compression in the case of YbBCO in all layers. The surface morphologies and microstructure of all samples were characterized by environmental scanning electron microscope (ESEM), atomic force microscope (AFM) and X-ray diffraction (XRD). The pole figure texture analyses of Ni substrate, Gd_1.802Ho_0.198O₃ buffer layers and YbBCO film have shown a single cube-on-cube textured structure.