Abstract: Bismuth-based filaments (ribbons) were successfully prepared in aluminum or silver alloys by processing and heat treatment. 1994, American Superconductor Company took the lead in preparing BSCCO/Ag with the length of 1000m and Jc of 1× 104A/cm2(77K, 0T). 1996, the Jc values of 1200m strip prepared by American Superconductor Corporation (ASC) and Sumitomo Corporation of Japan both exceeded 1.2× 104A/cm2 (77K, 0T), which can be stably produced. According to the current research results, it can be considered that the Jc value of Bi-based materials will be greatly improved by further improving the process parameters, increasing the strip density and grain structure, improving the connectivity between grains and introducing effective flux pinning centers. In addition, significant progress has been made in improving the mechanical strength of Bi series wire (tape) materials through multi-core and alloying of matrix materials.
2. Research progress of flexible metal-based YBCO tape.
YBCO superconductors have strong intrinsic pinning characteristics in the liquid nitrogen temperature range, but it is difficult to realize their grain orientation by conventional processing technology. Therefore, although long wires (ribbons) can be prepared by the PIT method and the methods of coating and post-heat treatment on ordinary metal substrates, their Jc values are all less than 103A/cm2(77K, 0T) and decrease rapidly with the increase of magnetic field. Inspired by the preparation of YBCO thin films with high Jc by epitaxial growth on single crystal substrates, two kinds of flexible baseband, "IBAD (LANL, USA)" and "RABiTS (ORNL, USA), were recently developed, and YBCO thin films were successfully grown on these baseband, and high JC tapes were obtained. Yttrium-stabilized zirconia (YSZ) was deposited on flexible metal strips (such as silver and nickel) for both baseband. ). Because the crystal lattices of YSZ and YBCO are very close, they have good chemical stability. On the one hand, they can induce the directional growth of YBCO crystals, on the other hand, they can act as a barrier to prevent YBCO from reacting with metal baseband. At present, the Jc values of YBCO superconductors prepared by pulsed laser deposition (PLD) and MOCVD on IBAD and RABiTS tapes have both exceeded the Jc values of NbTi and Nb3Sn at 4.2K under the strong magnetic field of 65K. For example, the maximum Jc of IBAD samples prepared by LANL in the United States is 106A/cm2(75K, 0T). The Jc of ORNL RABiTS tape has also reached 7× 105A/cm2(77 K, 0T). Although there are still some technical difficulties in the preparation of long tape, the high Jc performance brought by this method shows a bright future for the high voltage application of high-temperature superconductors in the temperature range of 77K. People call it the second generation of high-temperature superconducting tape after BSCCO tape by PIT method, and have invested a lot of manpower and material resources.
(4) movies
In order to obtain high-performance high-temperature superconducting devices, high-quality thin films are needed. However, high-temperature superconductors are compounds composed of many elements (at least four), and they often have several different phases. In addition, high-temperature superconductors are highly anisotropic, which makes it quite difficult to prepare high-quality high-Tc superconducting films. Nevertheless, after ten years of unremitting efforts by scientists all over the world, great progress has been made. The Tc of high-quality epitaxial YBCO films is above 90K, and the critical current density Jc of 77K under zero magnetic field exceeds 1× 106A/cm2. The technology has been basically mature, and a number of high temperature superconducting thin film electronic devices have come out.
Third, the application of high temperature superconducting materials
Superconducting materials have the characteristics of high current carrying capacity and low energy consumption, which make them widely used in energy, transportation, medical care, major scientific and technological projects and modern national defense. At present, large-scale applications have been formed in two aspects. First, major scientific and technological projects, mainly large particle accelerators for high-energy physics research, such as the large proton collider LHC, which is being built in Europe with a circumference of 27 kilometers, and thermonuclear fusion reaction devices, such as ITER and LHD. Second, MRI, a nuclear magnetic resonance imaging system, is widely used in medical diagnosis and nuclear magnetic resonance spectrometer NMR, which has high scientific and application value.
According to the current development of HTS wires, bismuth-based wires (tapes) that have been commercialized are called the first generation wires, while Y-Ba-Cu-O coated wires that may be commercialized in the future are called the second generation wires. Improving the performance of HTS materials and reducing the cost will be an important issue in the future. From the application point of view, the cost of superconducting wire is calculated according to the price per thousand Mi An. Therefore, in addition to reducing raw materials and processing costs, increasing the current carrying capacity of wire rod will also greatly reduce costs. Most HTS applications require the properties of wire rod-price 10 USD/card? M or so, because this price is equivalent to the performance price of copper conductor in practical application. 1999, the price of bismuth -2223 has been lowered from 1998 to 1000 USD/card? M is reduced to $300, and the cost is expected to be reduced to $50 in five years.
What is exciting is that the discovery of the new high-temperature superconductor magnesium diboride (an intermetallic compound, TC ~ 40K) from June 5438 to February 2000 set off a new upsurge of high-temperature superconductivity. Now many superconducting research groups all over the world are researching and developing around the clock. Several major research institutions of superconducting materials in China have developed single-phase magnesium diboride superconductors, and their characteristics are being deeply studied, and the research and development of wires are also being carried out simultaneously. Compared with oxide high-temperature superconductors, magnesium diboride has the characteristics of simple structure, good stability and easy production. More importantly, it has a higher critical current density (JC > 105A/cm2), and its cost performance is considered to be better than that of niobium-titanium superconductors, so it can be used in 20k refrigerators.
No liquid nitrogen is needed. It is predicted that the magnesium diboride superconductor will soon reach the practical level, which indicates that another new era of superconducting materials may come.