Fabrication Of A New Cu-Ni Bi-metallic Substrate And Deposition Of La₂Zr₂O₇ (LZO) Film On Metallic Substrate By Chemical Solution Deposition Process

In 1990's, researchers in USA and in Japan found that it was possible that a textured YBCO film with high superconducting property could be deposited on a textured metallic substrate to obtain YBCO tape. This idea provides a new route to fabricate YBCO superconductors, and this new complex of YBCO tape is called coated conductor. The structure of coated conductor can be divided into four parts:metallic substrate, buffer layers, YBCO layer and protecting layer. Because coated conductors have better superconducting properties under high magnetic field than that of Bi-2223/Ag tapes, development of fabricating process of coated conductors has attracted the attention of material researchers in recent ten years. Now, developing a sharp cube-textured metallic substrate with good mechanical property and with low magnetic moment. simplifying the architecture of buffer layers and developing an economical fabricating process of YBCO layer are three highlights in material researching field of coated conductors.In order to develop an economical fabricating process of coated conductors, a new Cu-Ni bi-metallic substrate with low magnetic moment was studied in this thesis, where the new Cu-Ni bi-metallic substrate was obtained by depositing a cube-textured Ni layer on a cube-textured Cu tape by electro-deposition, and other main discussion in this thesis was about how to fabricate La2Zr2O7(LZO) oxide buffer layer by chemical solution deposition (CSD) process.In order to decrease the AC loss, Cu should be considered as a potential substrate material for coated conductors. But the disadvantages of Cu substrate are obvious:low thermal stability of texture and low oxidization resistance. These disadvantages can be overcome by depositing a Ni layer on the Cu tape. The magnetic moment of this new Cu-Ni bi-metallic substrate becomes low after deposited the oxide buffer layer on it, which is due to diffusion between Ni layer and Cu layer. In this thesis. fabricating a cube-textured Cu tape by a rolling-recrystallization treatment was studied firstly, and the influences of total rolling deformation rate, thickness reduction pre pass, recrystallization temperature and annealing time were mainly focused. Beside the parameters of process, the texture un-uniformity in cross-section of Cu tapes was also discussed. Secondly, deposition of a Ni layer on the cube-textured Cu tape was studied. Conductions to obtain a cube-textured Ni deposit and influence of deposition parameters on the final texture of Ni layer were mainly focused. Results showed that, only if the rolling deformation rate was larger than a critical deformation rate (＞95.8%). was the cube-textured Cu tape obtained. The other parameters of rolling-recrystallization process didn't decide whether the cube-textured Cu tapes were obtained or not, they would influence the sharpness of cube texture of Cu tapes. The texture of Ni layer was influenced not only by depositing parameters, but also the surface characteristics of Cu tapes. The magnetic hysteresis loop of the Cu-Ni bi-metallic substrate indicated that the magnetic loss induced by this new substrate was lower than one induced by a Ni-5at%W substrate.Requirements to buffer layers, transferring texture from substrate to YBCO layer and preventing diffusion of metal and oxygen, ask that a successful architecture of buffer layers is composed of several oxide layers. Comparing with other architectures of buffer layers, the architecture of La2Zr2O7/CeO2 attracts many researchers'attention. The characteristics of pyrolysis of LZO precursor solution and the phase formation of LZO powder were studied in this thesis, and influences of parameters of chemical solution deposition (CSD) process on the epitaxial growth of LZO film on a metallic substrate was also analyzed roundly. Firstly, the influences of c(2×2)-S which was obtained on a metallic substrate by a simply sulfuration process put forward by myself on the expitaxial growth of LZO film was discussed. Results indicated that the c(2×2)-S superstructure could control efficiently the orientation of the initial LZO layer which formed on metallic substrates. It is helpful for obtaining stably a cube-textured LZO film on metallic substrates. Secondly, analyzing to the inhibiting factors to the epitaxial growth of LZO film implied that the residual carbon which had existed in precursor LZO film influenced strongly the epitaxial growth of LZO film. The influences of residual carbon on the finial texture of LZO film were decided by the distribution gradient of residual carbon in LZO precursor film. A sharp distribution gradient of residual carbon was welcome in order to deposit a sharper cube-textured LZO film with a good surface crystallinity and with good surface texture on metallic substrates by CSD process. Finally, the success of depositing a cube-textured CeO2 film on the LZO film implied that the surface characteristics of LZO film deposited by CSD process were very good.In summary, a new Cu-Ni bi-metallic substrate with low magnetic moment was developed successfully, and a La2Zr2O7 buffer layer with good surface characteristics (good surface crystallinity and good surface texture) was deposited successfully on Ni-based substrates (the Cu-Ni bi-metallic substrate, Ni-5at%W substrate). These results lay the powerful foundation for developing an economical fabricating process of coated conductors.