Development of buffer layers by chemical solution deposition for YBCO coated conductors

Short length YBCO coated conductors have been fabricated by vacuum thin film deposition techniques. However, the fabrication process increases the cost, and makes them impractical to use for commercial applications even if they are fabricated in kilometer lengths. YBCO coated conductors could be available in the market with a cheaper price by developing non-vacuum deposition techniques. The objective of this research was to investigate development of buffer layers by chemical solution deposition technique for YBCO coated conductors. Buffer layer structures are mainly used to prevent metal ion diffusion, and to reduce the lattice mismatch between YBCO and the metallic substrate. The technical approach, which was adapted here, is the reel-to-reel sol-gel dip coating process to fabricate long length coatings by developing buffer layers' chemical solutions. Rolling assisted biaxially textured Ni substrates were used for deposition of buffer layers. Cold rolled Ni strips were heat-treated at certain conditions to form biaxially textured structure, which became templates for textured growth of buffer layers that is necessary to obtain high critical current in the coated conductors. CeO₂ was chosen as a buffer layers because it has been recognized as one of the best cap layers. Growth of highly textured, crack free, pinhole free and smooth CeO₂ buffer layers have been demonstrated by chemical solution deposition technique on biaxially textured substrates. A new buffer layer with pseudocubic lattice parameters matching YBCO, (Eu_0.893Yb_0.107)₂O₃, was developed for the first time by using a mixture of Eu₂O ₃ and Yb₂O₃ to eliminate lattice mismatch, which adversely affected the critical current of the coated conductors. Highly textured (Eu_0.893Yb_0.107)₂O₃ buffer layers were deposited on biaxially textured Ni substrates by chemical solution deposition technique. Finally, the growth of CeO₂ and (Eu_0.893Yb _0.107)₂O₃ buffer layers were investigated on oxide layers because both CeO₂ and (Eu_0.893Yb_0.107) ₂O₃ are used as cap layers. CeO₂ buffer layers were deposited on Gd₂O₃ buffer layers and (Eu_0.993 Yb_0.107)₂O₃ buffer layers were deposited on CeO₂/Gd₂O₃ buffer layers structure. It has been demonstrated that biaxially textured buffer layers can be grown on both biaxially textured metallic substrates and oxide thin films. These results are very promising for applicability of chemical solution deposition technique for coated conductors fabrication.