Research On Fabrication And Flux Pinning Properties Of Higt-temperature Superconducting Films By MOCVD

Owning to its low ac loss, high irreversibility field and excellent current carrying capability, the second generation High- Temperature Superconductor(HTS) film, especially YBa2Cu3O7-δ, tape, which has superior application potential on energy, electricity, national defence and other fields. Among different fabrication methods, Metal-Organic C hemical Vapor Deposition(MOCVD) has received extensive attention due to its high growth rate and good uniformity of the epitaxial films. In this thesis, high-performance YBCO films were deposited on single crystal LaAlO3(001) via MOCVD, which is essential for developing kilometer-class high performance HTS tape.The main content is as follows:1 The effects of the mole ratio of three metal-organic sources on microstructure and property of YBCO film were investigated. The effects of Ba/Y mole ratio,Cu/Y mole ratio and Y contents the crystal structure, surface topograp hy and critical current density of YBCO film have been systematically explored. The results showed that the critical current density and the amount and size of the second phase were closely related with three metal-organic sources mole ratio.2 The effect of the temperature and film thickness on thecrystal structure, surface topography and critical current density of the film was discussed. By adjusting the deposition temperature, the a-axis growth and decomposition of the YBCO film were inhibited. Meanwhile, the relationship between film thickness a nd the critical current density of YBCO film was discussed.3 In this paper, we systematically studied the flux pinning effect by doping YBCO film with rare earth ion Gd, and the effect of ion doping on the crystal structure, surface topography and critical current density of the flim was investigated. The results demonstrated that YBCO film performance can be improved remarkably by flux pinning with rare earth ion Gd. When the mole ratio of Gd:Y=1:1, the critical current density is the best.4 YBCO flim was deposited on Y2O3/YSZ/CeO2(YYC) buffer layer. We investigate the relationship between heater treating temperature and crystal structure, surface topography and critical current density of YBCO film. By modulating the depositon temperature and the metal-organic sources mole ratio, YBCO flim with critical current density(Jc at self- field, 77 K) of 1.4 MA/cm2 were successfully fabricated.