Fabrication And Optimization Of Bi-2212High Temperature Superconducting Thick Films

thick film is of great importance for the practical applications of high temperature superconductors, due to its advantages, such as easy fabrication, low cost, etc. The most commen applications of Bi-2212thick films involve magnet shielding, basement circuitry system, and high-frequency instrument, etc. In the study, some optimizations have been performed based on the combination of traditional dip-coating process (DIP) and partial melting process (MP). Bi-2212/Ag thick films have been obtained with optimized transport properties. Based on this method, it is provided an easy and cheap way to judge the quality of precursor powders for the fabrication of2212tapes and wires. Main results are given as follows:Firstly, the fabrication process of Bi-2212thick films has been optimized. All the thick films have been fabricated based on the traditional dip-coating process. During the partial melting process, the influences of partial melting temperature Tmax and cooling rate Rc have been systematically investigated. It can be concluded that with partial melting temperature of885℃and cooling rate of2℃/h, the intergrain connections have been enhanced. On the other hand, a cold-pressing and rolling process have been performed respectively to optimize the fabrication method of Bi-2212thick films. The results exhibited that the cold-pressing process after dip-coating can obviously improve the superconducting properties by increasing the density of films and enhancing the intergrain connections. The optimized critical current density of13.8kA/cm2has been obtained.Precursor powders with different Bi ratios (BixSr1.96Ca1.0Cu2.0O8+δ, χ=2.0,2.1,2.2, and2.4), and Cu ratio,(Bi2.1Sr1.96Ca1.0CuvO8+δ, y=2.0,2.1,2.2, and2.4) have been prepared respectively with modified co-precipitation process (MCP). Bi ratio of x=2.1has been proved to be the most suitable for the co-precipitation process, with the real composition almost equal to the nominal composition. Therefore, Bi ratio of2.1has been applied in the following researches to ensure the repeatability of chemical compositions. The influences of Cu ratio on the sintering process of2212have also been investigated. Slight increase of Cu ratio can accelerate the forming rate of2212phase.In order to prove the consistency of transport properties between Bi-2212thick films and tapes, Bi-2212thick films with different Cu ratios have been prepared with optimized dip-coating process and optimized partial melting parameters. The thick film with Cu ratio of y=2.2exhibited the best superconducting properties. Meanwhile, Bi-2212single-filament tapes with the composition of Bi2.1Sr1.96Ca1.0CuyO8+δ, y=2.0,2.2, and2.4have also been prepared with the combination of powder in tube (PIT) process and partial melting process. The results showed that with the Cu ratio of y=2.2, the tapes exhibit the best texture and intergrain connections, therefore the superconducting properties is the highest. The critical current of24A can be obtained, corresponding to the critical current density of6.6kA/cm2(77K,O T). The best composition for tapes is consistent with that for thick films, which can confirm the effectiveness of applying thick films to judge the quality of precursor powders.