A superconducting alloy, Nb-Ge alloy, was discovered in 1973, and its critical superconducting temperature was 23.2K, which remained nearly 13 years.
1986, the research center of IBM company in Zurich, Switzerland reported that an oxide (La, Ba, Cu oxide) has a high temperature superconductivity of 35K. Since then, scientists have made new research results almost every few days.
1986, the critical superconducting temperature of superconducting materials studied by Bell Laboratories reached 40K, which crossed the "temperature barrier" of liquid hydrogen (40K).
During the period of 1987, Zhu Jingwu, a Chinese-American scientist, and Zhao Zhongxian, a scientist from China, successively raised the critical superconducting temperature to above 90K, and the "temperature barrier" (77K) of liquid nitrogen was also broken. At the end of 1987, thallium, barium, calcium, copper and oxygen materials increased the critical superconducting temperature to 125K, and in just over a year from 1986- 1987, the critical superconducting temperature increased by nearly 100K.
Scientists from Germany, France and Russia have observed the so-called magnetic * * vibration mode in the single copper oxide layer TL2Ba2CuO6+δ by neutron scattering technology, which further confirms the universality of this mode in high temperature superconductors. This discovery is helpful to the study of the mechanism of copper oxide superconductor.
High-temperature superconductors have a high superconducting transition temperature (usually higher than the temperature of nitrogen liquefaction), which is beneficial to the wide application of superconductivity in industry. It has been 16 years since the discovery of high-temperature superconductors, but the research on its many characteristics different from conventional superconductors and its micro-mechanism is still in a rather "primary" stage. This is not only reflected in the fact that no single theory can fully describe and explain the characteristics of high-temperature superconductors, but also in the lack of unified "intrinsic" experimental phenomena that are common in different systems. The results reported in this issue of Science magazine mean that a long-term puzzle in the field of neutron scattering may be solved.
As early as 199 1 year, French physicists found a weak magnetic signal in the double copper oxide layer YBA2Cu3O6+δ superconductor single crystal by neutron scattering technology. Subsequent experiments show that this signal will only be significantly enhanced when the superconductor is in superconducting state, which is called magnetic * * * vibration mode. This discovery shows that the spin of electrons produces collective orderly motion in a cooperative way, which is not available in conventional superconductors. This collective movement may participate in the pairing of electrons and be responsible for the superconducting mechanism, which is similar to the lattice vibration that causes electron pairing in traditional superconductors. However, the same phenomenon cannot be observed in another superconductor La2-xsrxCuO4+δ (single copper oxide layer). This makes physicists suspect that this magnetic vibration mode is not a common phenomenon of copper oxide superconductors. In 1999, this magnetic vibration signal was also observed in Bi2SR2CaCu2O8+δ single crystal. However, because Bi2SR2CaCu2O8+δ, like YB2U3O6+δ, has the structure of double copper oxide layer, the confusion about whether the magnetic vibration mode is a special feature of double copper oxide layer or a "universal" phenomenon has not been completely solved.
The ideal candidate should be a typical high-temperature superconducting crystal, with the structure as simple as possible and only a single copper oxide layer. The difficulty is that because the interaction between neutrons and matter is very weak, neutron scattering experiments can only be carried out with crystals large enough. With the maturity of neutron scattering technology, the requirement of crystal size has been reduced to 0. 1 cm 3. With the development of crystal growth technology, the size of TL2Ba2CuO6+δ single crystal has entered the millimeter order, and it is an ideal candidate material. Scientists arranged 300mm Tl2ba2Cuo6+δ single crystals in the same standard according to crystallographic orientation to form an "artificial" single crystal, which met the requirements of neutron scattering "in advance". After nearly two months' collection and repeated verification of scattering spectra, it is finally shown by conclusive experimental data that there are also magnetic * * * vibration modes on such an almost ideal high temperature superconducting single crystal. This result shows that magnetic vibration mode is a common phenomenon of high temperature superconductivity. The absence of magnetic mode in La2-xsrxCuO4+δ system is only an exception to the "universality" phenomenon, which may be related to the particularity of its structure.
The theoretical and experimental study of magnetic vibration mode and its interaction with electrons has always been one of the hot spots in the field of high temperature superconductivity. The above results will attract the attention and interest of many physicists.
The 1980s was the golden age of superconducting exploration and research. Organic superconductors were synthesized in 198 1 year. 1986, Miao Lei and Bernoz discovered a ceramic metal oxide LaBaCuO4, which is composed of barium, lanthanum, copper and oxygen, and its critical temperature is about 35K. Because ceramic metal oxides are usually insulating substances, this discovery is of great significance, so Miao Lei and Bernoz won the Nobel Prize in physics.
1987 a new breakthrough has been made in the exploration of superconducting materials. Zhu Jingwu, a physicist at the University of Houston, and Zhao Zhongxian, a physicist at the Institute of Physics, Chinese Academy of Sciences, have successively developed superconducting material YBCO (YBCO) with a critical temperature of about 90K.
At the beginning of 1988, Japan developed a Bi-Sr-Ca-Cu-O superconductor with a critical temperature of 1 10K. At this point, mankind finally realized the dream of superconductors in the liquid nitrogen temperature region and achieved a major breakthrough in the history of science. This superconductor is called high temperature superconductor because its critical temperature is higher than that of liquid nitrogen (77K).
Since the discovery of high temperature superconducting materials, a superconducting boom has swept the world. Scientists also found that the critical temperature of thallium compound superconducting materials can reach 125K, and that of mercury compound superconducting materials can reach 135K ... If mercury is placed under high pressure, its critical temperature will reach an incredible 164K.
1997, researchers found that gold indium alloy is both a superconductor and a magnet when it is close to absolute zero. 1999 Scientists found that Ru-Cu compounds have superconductivity at 45K. Because of its unique crystal structure, the compound will have great application potential in computer data storage.
In order to prove that the resistance of (superconductor) is zero, scientists put a lead ring in a space with a temperature lower than Tc=7.2K, and induced current in the ring by electromagnetic induction. The results show that the current in the loop can last for two and a half years, from March 1954 to September 5 1956. This indicates that there is no power loss in the ring. When the temperature rises above Tc, the ring changes from superconducting state to normal state, the material resistance suddenly increases, and the induced current disappears immediately.
1. Superconducting technology
19 1 1 year, Cameron-Anis of Leiden University in the Netherlands accidentally found that when mercury cooled to -268.98℃, the resistance of mercury suddenly disappeared. Later, he found that many metals and alloys have the characteristics of losing resistance at low temperature similar to the above mercury. Because of its special conductivity, Cameron-anis called it superconducting state. Cameron won the Nobel Prize in 19 13 for this discovery.
This discovery caused a worldwide shock. After him, people began to call conductors in superconducting state "superconductors". The DC resistivity of superconductors suddenly disappears at a certain low temperature, which is called zero resistance effect. Without the resistance of the conductor, the current will not cause heat loss when it flows through the superconductor, and the current can flow a large current in the conductor without resistance, thus generating a super-strong magnetic field.
1933, meissner and Olsenfeld in the Netherlands discovered another extremely important property of superconductors. When the metal is in superconducting state, the magnetic induction intensity in this superconductor is zero, but the original magnetic field in the body is squeezed out. The experiment of single crystal tin ball shows that when the tin ball transits to superconducting state, the magnetic field around the tin ball suddenly changes, and the magnetic field lines seem to be excluded from the superconductor at once. People call this phenomenon "Messner effect".
Later, people also did an experiment: in a shallow tinplate, a small but highly magnetic permanent magnet was placed, and then the temperature was lowered to make the tinplate superconducting. At this time, we can see that the small magnet actually left the surface of the tinplate and floated slowly.
Messner effect is of great significance and can be used to judge whether a substance has transcendence.
In order to make superconducting materials practical, people began to explore the process of high temperature superconductivity. From 19 1 1 to 1986, the superconducting temperature increased from 4.2K Hg to 23.22K(OK =-273℃). The superconducting temperature of Ba-La-Cu oxide was found to be 30 degrees in 65438+86 years1October, and it was set at 40.2K on February 30, 65438+87 years1October, rising to 43K, and then quickly rising to 46K and 53 K. In February, 15 years, 98K superconductors were found.
Superconducting materials and superconducting technology have broad application prospects. Meissner effect in superconductivity makes it possible for people to make superconducting trains and ships by using this principle. Because these vehicles will run in a frictionless state, their speed and quiet performance will be greatly improved. Superconducting train has successfully carried out manned feasibility test in 1970s. Japan started its trial operation from 1987, but there were frequent breakdowns, probably due to bumps caused by high-speed driving. The superconducting ship was launched on June 27, 1992, and has not yet entered the practical stage. There are still some technical obstacles in manufacturing vehicles with superconducting materials, but it is bound to trigger a wave of vehicle revolution.
The zero-resistance characteristics of superconducting materials can be used to transmit electricity and manufacture large magnets. Ultra-high voltage transmission will have great losses, which can be minimized by using superconductors, but superconductors with higher critical temperatures have not yet entered the practical stage, thus limiting the adoption of superconducting transmission. With the development of technology and the appearance of new superconducting materials, the hope of superconducting power transmission will be realized in the near future.
The existing high-temperature superconductors are still in the state that they must be cooled by liquid nitrogen, but they are still considered as one of the greatest discoveries in the 20th century.
2. Superconducting technology and its application
Bill Lee
19 1 1 year, the Dutch scientist Agnes cooled mercury with liquid helium. When the temperature drops to 4.2K, it is found that the resistance of mercury disappears completely. This phenomenon is called superconductivity. 1933, two scientists, meissner and Oxenfield, found that if the superconductor is cooled in a magnetic field, when the material resistance disappears, the magnetic induction line will discharge from the superconductor and cannot pass through it. This phenomenon is called diamagnetism.
Superconductivity and diamagnetism are two important characteristics of superconductors. The temperature at which the superconductor resistance is zero is called the superconducting critical temperature. After decades of efforts by scientists, the magnetoelectric barrier of superconducting materials has been crossed, and the next difficulty is to break through the temperature barrier, that is, to seek high-temperature superconducting materials.
Strange superconducting ceramics
In 1973, a superconducting alloy, Nb-Ge alloy, was discovered, and its critical superconducting temperature was 23.2K, which remained for 13 years. 1986, the research center of IBM Company in Zurich, Switzerland reported that an oxide (La-Ba-Cu-O) has high-temperature superconductivity of 35K, which broke the traditional concept that oxide ceramics are insulators and caused a sensation in the world scientific community. Since then, scientists have worked hard against time, and new research results have appeared almost every few days.
At the end of 1986, the critical superconducting temperature of oxide superconducting materials studied by Bell Laboratories reached 40K, which crossed the "temperature barrier" of liquid hydrogen (40K). 1987 In February, Zhu Jingwu, a Chinese-American scientist, and Zhao Zhongxian, a China scientist, successively raised the critical superconducting temperature above 90K on YBCO materials, and the forbidden zone of liquid nitrogen (77K) was miraculously broken. At the end of 1987, thallium, barium, calcium, copper and oxygen materials raised the critical superconducting temperature to 125K. In just over a year, the critical superconducting temperature was actually raised by 100K, which is a miracle in the history of material development and even the history of science and technology!
The continuous appearance of high-temperature superconducting materials paves the way for superconducting materials to move from laboratory to application.
Supergroup superconducting magnet
The most attractive applications of superconducting materials are power generation, transmission and energy storage.
Because superconducting materials have zero resistance and complete diamagnetism in superconducting state, they can obtain a steady-state strong magnetic field above 654.38+ million gauss with very little power consumption. Using conventional conductors as magnets to generate such a large magnetic field needs to consume 3.5 MW of electric energy and a lot of cooling water, and the investment is huge.
Superconducting magnets can be used to manufacture AC superconducting generators, MHD generators and superconducting transmission lines.
Superconducting generator In the field of electric power, the magnetic field intensity of the generator can be increased to 50,000 ~ 60,000 gauss by using superconducting coil magnets, and there is almost no energy loss. This kind of generator is an AC superconducting generator. Compared with the conventional generator, the single unit capacity of superconducting generator is increased by 5 ~ 10 times, reaching 100MW, while the volume is reduced by 1/2, the weight of the whole machine is reduced by 1/3, and the power generation efficiency is improved by 50%.
Magnetohydrodynamic generator Magnetohydrodynamic generator is also inseparable from the help of superconducting strong magnets. Magnetic fluid power generation takes high-temperature conductive gas (plasma) as the conductor, and generates power through a strong magnetic field with a magnetic field intensity of 50,000-60,000 gauss at high speed. The structure of MHD generator is very simple, and the high-temperature conductive gas used for MHD power generation can be reused.
Superconducting materials used for superconducting transmission lines can also be used to make superconducting wires and superconducting transformers, so as to transmit electricity to users almost without loss. According to statistics, at present, about 15% of electric energy is lost on transmission lines. In China alone, the annual power loss exceeds 6,543,800 billion kWh. If we switch to superconducting power transmission, the energy saved is equivalent to building dozens of large power plants.
Wide application of superconductivity
High temperature superconducting materials are widely used, which can be roughly divided into three categories: high current applications (high current applications), electronic applications (low current applications) and diamagnetic applications. High current applications are superconducting power generation, transmission and energy storage mentioned above; Electronic applications include superconducting computers, superconducting antennas and superconducting microwave devices. Diamagnetism is mainly used in maglev trains and thermonuclear fusion reactors.
Superconducting maglev train uses the diamagnetism of superconducting materials to put superconducting materials on permanent magnets. Because the magnetic field lines of the magnet can't pass through the superconductor, there will be repulsive force between the magnet and the superconductor, which will make the superconductor suspend above the magnet. This magnetic levitation effect can be used to make high-speed superconducting magnetic levitation trains.
Superconducting computer High-speed computer requires the components and connecting wires on the integrated circuit chip to be densely arranged, but the densely arranged circuits will generate a lot of heat when working, and heat dissipation is a difficult problem for VLSI. In the VLSI of superconducting computer, superconducting devices with near-zero resistance and ultra-micro heating are used as interconnection lines between components, so there is no heat dissipation problem and the computing speed of the computer is greatly improved. In addition, scientists are studying making transistors with semiconductors and superconductors, or even making transistors entirely with superconductors.
When the nuclear fusion reaction is carried out in the "magnetic shell" of a nuclear fusion reactor, the internal temperature is as high as 1 100-200 million℃, and any conventional substance cannot contain these substances. The strong magnetic field generated by superconductor can be used as a "magnetic shell" to enclose and restrain the ultra-high temperature plasma in thermonuclear reactor, and then release it slowly, thus making the controlled nuclear fusion energy become a new energy with broad prospects in 2 1 century.