The Study On La₂Zr₂O₇ Thick Buffer Layer And Orientation By Chemical Solution Deposition

The Second Generation(2G) high temperature coating superconductor YBa2Cu3O7-δ(YBCO) has been attracted extensive attention due to its broad application prospect in electric power, transportation and other fields. The buffer layers act as transfering the texture and diffusion barriers as the important part of coated conductors. At present, the films are prepared basically using a combination of physical and chemical method. In order to reduce production cost and simplify the structure of buffer layers, thick LZO buffer layers were prepared on highly textured Ni-5at.%W substrates using chemical solution deposition(CSD) approach, and the orientation relationship between film and substrate was explored. The summaries are as following:The stability of the precursor solution has been studied, and the LZO film nucleation temperature was determined using Metal Organic Deposition. The influence of concentrations of precursor solution, annealing temperature and thickness on LZO films were investigated systematically. The optimal parameters were as follows: annealing temperature 1150 oC, annealing time 60 min and concentration of precursor solution 0.8mol/L. The value of full width at half maximum(FWHM) of(222) φ-scan and rocking curve of(400) of LZO buffer layer is 6.19°, 6.52o(RD) and 8.41o(TD), respectively. The texture component(<10o) of thick LZO films reach 98 %, which exhibit a smooth, dense surface by SEM and AFM.The YBCO film was deposited on thick LZO/Ni5 W buffer layer architecture, and YBCO/LZO(2 layers)/Ni5 W film exhibits optimal performance. The surface of this YBCO film contains slight numbers of a/b-axial grains and Cu-rich phase. The FWHM of in-plane and out-plane scan of this YBCO film is 7.34° and 5.05o. Moreover, the YBCO/CeO2/LZO/Ni5 W superconducting film has been prepared and the value of FWHM of in-plane and out-plane scan is 10.49° and 9.1o, respectively.We have discovered the orientation relationship between film and substrate associated with thickness of film. The epitaxial texture mechanism of film was investigated by Electron Back Scattering Diffraction(EBSD) and the texture relationship between film and metal substrates was discussed preliminarily. The LZO grains have large out-plane misorientation and were not detected by EBSD, which grown at grain boundaries of substrates. The LZO grains tend to nucleate at grain boundaries of substrates and grow with cube orientation when the thickness of film is small. The orientation of LZO grains gradually shift from cube to 45o rotating cube orientation with the increasing thickness and releasing stress of film.Accordingly, focusing on industrialization of coating conductor, this thesis has prepared buffer layer and superconducting film by chemical solution deposition. Firstly, the thick LZO films have been prepared with optimized annealing process. Secondly, the YBCO film with c axsis orientation has been prepared with CSD technology. Finally, the orientation relationship between film and substrate associating with thickness of film has been discovered, and the mechanism of texture evolution was discussed preliminarily.