Preparation Of SrTiO₃and La_0.4Sr_0.6TiO₃Buffer Layers And Ybacuo Superconductive Layers On Textured Ni-W Substrates

The second-generation high-temperature superconductor (HTS) tapes YBCO coated conductors have been a key development direction of high-temperature superconductive materials due to its advantages of having a higher performance and less power loss of the exchange in magnetic field and temperature. Because there are lattice mismatch and inter-diffusion of oxygen and metal atoms for fabricating YBCO tape, it is necessary to deposite buffer layers between metal substrates and YBCO layers. The metal organic deposition (MOD) process is considered to be one of the promising methods as it is a simple, low cost, non-vacuum and effective deposition method.In this paper, SrTiO3and Lao.4Sro.6Ti03buffers were prepared on Ni-5at.%W alloy substrates by MOD method, on which YBCO superconductor films were deposited. The XRD, SEM and optical microscopy were adopted to study the crystal structure and surface morphology of films. Further, the influences of the process conditions such as seed layers, heat treatment and atmosphere conditions on the properties of films were discussed.STO buffer layers had been fabricated on Ni-5at.%W alloy substrates by MOD method. This process adopted strontium acetate and butyl titanate as reagents, glacial acetic and methanol as solvents, acetylacetone as stabilizing agent to prepare precursor solutions. The effect of annealing temperature and thickness of STO seed layer and sintering time on STO buffer layer were fully discussed. The results showed that the optimal conditions of preparing STO buffer layers were STO grain growth on three-layered STO seed layers annealing at880℃. Annealed at950℃for120minutes, STO thin films with c-axis oriented grain growth were prepared. The surface of STO films was smooth and dense with fine particle, and no crack and holes. Doping of Lanthanum element in the precursor solution of STO seed layer benefited (200) oriented grain growth of STO films.Multi-functional LSTO buffers had been fabricated on Ni-5at.%W alloy substrates by MOD method. This process adopted strontium acetate, lanthanum acetate and butyl titanate as reagents, glacial acetic and methanol as solvents, acetylacetone as stabilizing agent to prepare precursor solutions. The effect of annealing temperature, different seed layers, annealing time, and cooling rate in high temperature stage on LSTO buffer layer were fully discussed. The results showed that the optimal conditions of preparing LSTO buffer layers were LSTO grain growth on LTO seed layers, annealing at950℃for120minutes and cooling rate at0.2℃·min-1in the high temperature stage. Then LSTO thin films with (00l) preferred orientation were prepared. The surface of LSTO films was smooth and dense, and the grains were small and uniform.Superconductive YBCO films had been obtained on the SrTiO3/NiW and La0.4Sr0.6TiO3/NiW structures. The prepared YBCO films had unobvious c-axis oriented grain growth. YBCO films deposited on STO buffer layers annealed at790℃and on LSTO buffer layers at820℃were continuous and dense, and the diffraction peaks of YBCO phase were stronger with the existing NiO. The oxidation of NiW substrates could be restrained at Ar-2%H2and Ar atmospheres or by enhancing the thickness of LSTO buffer layers. For preparation of YBCO coated layers, the oxidation phenomenon of NiW substrates will be the key problem of preparing YBCO superconductive tapes by chemical solution deposition method, which should be overcome in the future.