Chemical Solution Deposition Prepared By Burn The Greenstone Type Buffer Layer

YBCO and BSCCO, high temperature superconductors working at liquid nitrogen temperature, have bright prospects in industry. The second generation high temperature YBCO coated conductor has better superconducting properties in high magnetic field at 77 K than the first generation Bi-2223/Ag superconducting tapes, therefore, YBCO is the primary material. The architectures of YBCO coated conductor consist of four layers:metal substrate, buffer layers, superconducting layer and protecting layer. The successful architecture of buffer layers is composed of several oxide layers that are prepared by expensive high-vacuum deposition technology. At present, the expensive price is hindering the application of the high temperature YBCO coated conductors. Aim at buffer layers, it is the future goal to explore multifunctional material and to use the economical chemical solution deposition (CSD) technology. In this thesis, rare-earth zirconium films and rare-earth molybdate films with pyrochlore structure prepared by CSD method are studied in order to provide experimental support for simplifying architecture of buffer layers and developing economical CSD technology. Detailed contents of this thesis are listed as following:1. RE2Zr2O7 (RE=Nd, Sm) prepared by CSD methodRE2Zr2O7 (RE=La, Nd, Sm and Gd) was respectively deposited on YSZ substrate by CSD method, the experiments were completed at the same conditions, in order to explore the possibility of Nd2Zr2O7 and Sm2Zr2O7 films as buffer layer for YBa2Cu3O7-8 coated conductors. By comparing and analyzing film composition, texture and surface topography of films, our results confirm that Nd2Zr207 and Sm2Zr2O7 films may be suitable buffer candidates for YBCO-coated conductors. In order to valuate the quality of Nd2Zr2O7 and Sm2Zr207 film as buffer layer, in this chapter, the CeO2 cap layer and YBCO superconducting layer were prepared on the template YSZ/NZO and YSZ/SZO by economical and efficient all-solution deposition method.①YSZ/Nd2Zr2O7/CeO2/YBCO:The value of full width at half maximum (FWHM) ofω-scan of the (006) peak of YBCO is 0.84°. SEM image shows that the surface of YBCO film on YSZ/Nd2Zr2O7/CeO2 template is smooth, dense and homogenous with crack-free and hole-free. The narrow transition temperature width△Tc explains the good quality of the sample. The critical current density of the sample is 0.8 MA/cm2. Above results indicate that the Nd2Zr2O7 film maybe a potential buffer layer for YBCO coated conductor.②YSZ/Sm2Zr2O7/CeO2/YBCO:The value of FWHM ofω-scan of the (006) peak of YBCO is 3.02°. SEM image shows that the surface of YBCO film on YSZ/Sm2Zr2O7/CeO2 template is crack-free and hole-free, but there is a-axis grain and the surface is not enough dense and homogenous. Compared with Nd2Zr2O7, Nd2Zr2O7 is more suitable as buffer layer.The optimal process for the Nd2Zr2O7 film with good c-axis texture on Ni-5at%W substrates in Ar-4%H2 is:pyrolysis of the wet film at 300℃for 1 h and then crystallization at 1000℃for 3 h. The process for Ni-W/Sm2Zn2O7 in Ar-4%H2 is:crystallization at 1000℃for 3 h. The gas speed is 2.2×10-2 m·s-1. Then it is confinned that the optimal film thickness is 60-70 nm for the buffer layer with pyrochlore structure.2. RE2Mo2O7 (RE=Nd,Sm and Gd) prepared by CSD methodMolybdenum (IV) dioxo acetylacetonate Mo(acac)2O2 and neodymium (Ⅲ) acetylacetonate Nd(acac)3 were selected as precursor materials and dissolved in methanol and propionic acid (volume ratio=3:2) to obtain the optimal precursor solution for preparation of Nd2Mo2O7 film by CSD method. The precursor solution was then spin-coated onto Ni-W substrate. The optimal process for the Nd2Mo2O7 buffer layer with good c-axis texture on Ni-W substrates in Ar-4%H2 is:pyrolysis of the dry film at 350℃for 1 h and then crystallization at 1000℃for 2 h, with total cation concentration of 0.4 M. Then it is confirmed by experiments that acetylacetone is of disbenefit to the crystallization and epitaxial growth of the film.Molybdenum (IV) dioxo acetylacetonate MoO2(acac)2 and samarium (Ⅲ) acetylacetonate Sm(acac)3 were selected as precursor materials and dissolved in methanol and propionic acid (volume ratio=2:3) to obtain the optimal precursor solution for preparation of Sm2Mo2O7 film by CSD method. Similarly, molybdenum (IV) dioxo acetylacetonate MoO2(acac)2 and gadolinium (Ⅲ) acetylacetonate Gd(acac)3 were selected as precursor materials and dissolved in methanol and propionic acid (volume ratio=4:1) to obtain the optimal precursor solution for preparation of Gd2Mo207 film by CSD method. The precursor solution was then spin-coated onto YSZ substrate. The optimal process for the Sm2Mo2O7 or Gd2Mo2O7 buffer layer with good c-axis texture on YSZ substrate in Ar are:pyrolysis of the dry film at 550℃for 1 h and then crystallization at 1000℃for 2 h, with total cation concentration of 0.4 M. It was confirmed by experiments that the volume ratio of solvents in the mixture and atmosphere in the heat treatment can effect epitaxial growth of the film.