Discoverer of superconductivity Kamerlin-Onnes. (1911), www.superconductors.org
The authors of the most popular model of superconductivity (BCS) are John Bardeen, Leon Kupper, John Schrieffer (1957), www.superconductors.org
The ancestors of HTSC. Nobel laureates Alex Müller and Georg Bednorz, www.superconductors.org
Discovery of mercury-containing HTSC phases at the Chemistry Department of Moscow State University - E.V. Antipov and S.N. Putilin, www.icr.chem.msu.ru
History of discovery
(Tretyakov Yu.D., Gudilin E.A., Chemical principles of obtaining metal oxide superconductors, Uspekhi Khimii, 2000, v. 69, no. 1, p. 3-40.)
The history of superconductivity is characterized by a chain of discoveries more and more complex structures, a kind of “chemical evolution” from simple to complex. It dates back to 1911, when the Dutch physicist Kamerlingh Onnes, who first obtained liquid helium and thereby opened the way to systematic studies of the properties of materials at temperatures close to absolute zero, discovered that at 4.2 K ordinary metallic mercury (a simple substance representing a "bad metal") completely loses electrical resistance. In 1933 Meissner and Ochsenfeld showed that superconductors (SC) are also ideal diamagnets, that is, they completely push out lines magnetic field from the volume of joint venture.
All this, in principle, opened up enormous possibilities for the practical application of superconductivity. However, on the way to realizing these ideas long time there was an insurmountable barrier - the extremely low temperature of transition to the superheated state, called the critical temperature (Tc). In the 75 years that have passed since the discovery of Kamerlingh Onnes, this temperature has only been raised to 23.2 K on the Nb 3 Ge intermetallic compound, and the generally accepted theories of superconductivity (BCS) have given rise to disbelief in the fundamental possibility of overcoming this temperature barrier.
In 1986 Bednorz and Müller discovered the ability of ceramics based on copper, lanthanum and barium oxides (La 2-x Ba x CuO 4) to transition to the superheated state at 30K. Complex cuprates of similar composition were synthesized in 1978. Lazarev, Kahan and Shaplygin, as well as French researchers two years later. Unfortunately, the electrical conductivity of these samples was measured only up to the boiling point liquid nitrogen(77K), which did not allow us to detect the effect of superconductivity.
The most important feature of the discovery of HTSC is that superconductivity was discovered not in traditional intermetallic compounds, organic or polymer structures, but in oxide ceramics, which usually exhibit dielectric or semiconductor properties. This destroyed psychological barriers and allowed, within a short time, to create new, more advanced generations of metal oxide joint ventures almost simultaneously in the USA, Japan, China and Russia:
February 1987 - Chu et al synthesize, using the idea of "chemical compression" to modify the structure, SP ceramics from barium, yttrium and copper oxides YBa 2 Cu 3 O 7-x with a critical temperature of 93 K, that is, above the boiling point of the liquid nitrogen.
In January 1988 Maeda et al synthesize a series of compounds with the composition Bi 2 Sr 2 Ca n-1 Cu n O 2n+4, among which the phase with n=3 has T c =108K.
A month later, Sheng and Herman obtained the superconductor Tl 2 Ba 2 Ca 2 Cu 3 O 10 c T c = 125K.
In 1993 Antipov, Putilin and others discovered a number of mercury-containing superconductors with the composition HgBa 2 Ca n-1 Cu n O 2n+2+ d (n=1-6). Currently, the HgBa 2 Ca 2 Cu 3 O 8+d (Hg -1223) phase has the highest known value of the critical temperature (135 K), and at an external pressure of 350 thousand atmospheres, the transition temperature increases to 164 K, which is only 19 K lower than the minimum temperature, recorded under natural conditions on the Earth's surface. Thus, SCs “chemically evolved”, going from metallic mercury (4.2 K) to mercury-containing HTSC (164 K).
In total, about 50 original layered HTSC cuprates are known to date. From time to time, sensational reports appear in the press about the creation of new SPs with temperatures above room temperature. And although copper-free SCs have been known for quite a long time, they have not yet been able to achieve any high temperature of transition to the SC state (record values of T c for copper-free SCs were achieved in Ba 1-x K x BiO 3 and in the interstitial phase based on fullerene (Cs 3 C 60) Separately, we should also mention the direction associated with attempts to synthesize “environmentally safe” HTSCs that do not contain heavy metals (Hg, Pb, Ba), for example, calcium oxycuprate phases obtained under high pressure.
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Discovery of superconductivity at high blood pressure in (TMTSF) 2PF6 and at normal pressure (TMTSF) 2C1O4 led to a noticeable revision of previously existing ideas regarding the prerequisites necessary for the emergence of a superconducting state. When studying crystal structures and interatomic distances in several compounds of the type (TMTSF) 2Ar Woodle came to the conclusion that the fulfillment of conditions (a) and (b) is not necessary. Moreover, in in this case metallic electrical conductivity does not occur due to overlap wave functions tg electrons of carbon, but due to the proximity of selenium atoms to each other, and such overlap occurs not only within the stack, but also between neighboring stacks. In other words, the crystals of the compounds under consideration are built from donor and acceptor layers and form quasi-two-dimensional structures. Essentially, all distances between selenium atoms do not exceed the van der Waals radii of the atoms. Magnetoresistance measurements gave the following results: the two-dimensional movement of electrons, which occurs in planes drawn through TMTSF stacks perpendicular to the plane of Figure 5 6.1, is coherent, and the movement between these planes is diffusional. As Woodl pointed out, when considering the available results on these compounds, at least three interesting questions arise: theoretical issues: (1) What is the reason for the nonlinear field dependence of electrical conductivity.
The discovery of superconductivity is the most a bright event in conductivity studies organic matter. It was first observed by Bechgaard, Jacobsen, Mortensen, Petersen and Tsorap and Jerome, Mazo, Ribot and Bechgaard in 1980 in a family of isostructural compounds with general formula(TMTSF) 2Ar, which are often called Bechgaard salts. Only the salt ClO4 exhibits superconductivity at atmospheric pressure and has a critical superconducting transition temperature Tc 1 K.
Since the discovery of superconductivity, the possibilities of technical use this amazing phenomenon.
Soon after the discovery of superconductivity in mercury, Kamerling-On - Nes and his collaborators were able to show that other metals, such as lead and tin, can transform into a superconducting state. Later, the superconducting properties of indium, gallium, and thallium were discovered, and in the 30s, with the development of new deep cooling methods, the number of superconductors was replenished with aluminum, zinc and other elements.
Very soon after the discovery of superconductivity, it was discovered that it can be destroyed not only by heating a sample, but also by placing it in a magnetic field.
It should be emphasized that the discovery of superconductivity and special properties quantum liquids does not at all cast doubt on the fact that real processes always irreversible to one degree or another.
So, it took almost half a century from the discovery of superconductivity before qualitative progress was made in understanding the nature of this amazing phenomenon and his consistent theory was created.
At the end of 1986, a report was published by K. Bednorets from Switzerland on the discovery of superconductivity of lanthanum - barium - copper oxygen ceramics at temperatures exceeding 30 K.
Important characteristic property superconductor is complete absence resistance at temperatures below the transition temperature Qc. Indeed, this was believed for quite a long period of time after the discovery of superconductivity. But a superconductor at temperatures below 6C is not just an ideal conductor: it is also an ideal diamagnetic, or, in other words, even in the presence of an external magnetic field, its internal density magnetic flux always equal to zero. It means that when a superconductor placed in a magnetic field is cooled, power lines inductions are pushed out of the material as soon as the superconducting transition temperature is passed.
The first property was discovered by Kamerlingh Onnes three years after he was able to liquefy helium, the second was discovered by Kapitsa 30 years after the discovery of superconductivity.
High temperatures of the superconducting transition can occur in such chemical compounds, the components of which have low Tc or are not superconductors at all. For example, nitrogen and carbon have no superconductivity, pure tungsten, zirconium and molybdenum have Tk 1 K, and for WC Tk - 10 K, for ZrN Tk 10 7 K, for MoC Tk - 14 3 K. The discovery of superconductivity in a polymer (SN) means the beginning of a new stage in the study of superconductivity. Alloys and compounds based on transition metals have the highest superconducting parameters.
Last years were the time active work in the area we have considered, and even more activity is expected in the future. Like from a cornucopia created high art organic chemists, compounds with new electrical properties. The discovery of superconductivity in more than one type of IRS has significantly expanded the prospects for determining the mechanism of superconductivity and, consequently, the synthesis of compounds with more high temperature superconducting transition. The synthesis of compounds that behave as quasi-one-dimensional and quasi-two-dimensional systems has opened up a vast field of activity for theorists who can now find exact solution transfer problems. Large scale has adopted the use of machine modeling, which is becoming a leading trend, for example, in the study of amorphous solids, where the movement of carriers has a hopping character. The continuing development of laser technology, which makes it possible to obtain short pulses of radiation with precisely defined wavelengths, has made it possible to excite specific internal modes and study their relaxation rates; Uniform linewidths are measured and mechanisms for such broadening are developed.
At first glance, it seems that the testimony of K. P. Yakovlev sharply contradicts one irrefutable historical fact: in the last short article by P. N. Lebedev, Advances in Physics in 1911, there is not a word about the planetary atom. But the point is that this article, written for the general public and published in the New Year's issue of Russian Gazette, was dedicated only to the indisputable and understandable successes of the 11th year. Thus, it did not mention the discovery of superconductivity, although an entire paragraph was devoted to the work of the Kammerling-Onnes cryogenic laboratory. The planetary atom did not belong to the category of indisputable and understandable truths.
Related grand opening the prospects are amazing. Creating materials with zero electrical resistance at temperatures easily maintained using an inexpensive refrigerant, liquid nitrogen (77 K), opens the way to solving a number practical problems, such as energy transfer without losses to long distances, the creation of miniature computer integrated circuits that are not subject to heat limitations, and the emergence of railways trains moving in the field of superconducting magnets, i.e. virtually frictionless. But the most remarkable thing is that in the first 75 years after the discovery of superconductivity, Tc was raised only to 23 K. Then, in just a few months, Tc was reached at 100 K. Surely other materials will be discovered that have superconductivity at room temperatures. Such a discovery would have strongest impact on our culture, comparable, probably, only with the results of the appearance of the transistor.
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Conductor resistance depends on temperature. When metals are heated, resistance increases; when metals are cooled, resistance decreases. When the temperature of the conductor approaches zero, a phenomenon called superconductivity may appear.
History of discovery
The discovery of superconductivity belongs to the Dutch physicist H. Kamerlingh-Onnes. He cooled mercury in liquid helium. At first the resistance gradually decreased, and then, upon reaching a certain certain temperature, the resistance dropped sharply to zero. This phenomenon was called superconductivity.
However, they were able to explain the essence of the phenomenon of superconductivity only in 1957. It is given on the basis quantum theory. With a huge simplification, superconductivity can be explained in the following way: electrons unite in ranks and move without colliding with crystal lattice. This movement is not at all similar to ordinary chaotic thermal movement.
In 1986, in addition to low-temperature superconductivity, it was discovered high temperature superconductivity. Created complex connections, which go into a state of superconductivity at a temperature of 100 K.
Properties of superconductors
- The critical temperature is the temperature at which a substance goes into a superconducting state. The phenomenon of superconductivity occurs in metals and their alloys at very low temperatures (approximately 25 K and below). There are reference tables that indicate the critical temperatures of certain substances.
- Since there is no resistance in superconductivity, therefore, no heat generation occurs when passing through a conductor electric current. This property of superconductors is widely used.
- For each superconductor there is critical value amperage, which can be achieved in a conductor without disturbing its superconductivity. This happens because when current passes, a magnetic field is created around the conductor. And the magnetic field destroys the superconducting state. Therefore, superconductors cannot be used to produce an arbitrarily strong magnetic field.
- When energy passes through a superconductor there is no loss of it. One of the areas of research modern physicists, is the creation of superconducting materials at room temperatures. If this problem can be solved, then one of the most important technical problems- transfer of energy through wires without loss.
Prospects
High temperature superconductivity- this is a very promising area of research, which may subsequently lead to new technical revolution in electronics, electrical engineering and radio engineering. According to the latest data in this area, the maximum critical temperature The superconductivity that was achieved is 166K.
We are gradually getting closer to the discovery of materials that will be superconducting at room temperatures. This will be a breakthrough in the world of technology. Electricity can be transmitted to any distance without loss.
The chaotic movement of the atoms of the conductor prevents the passage of electric current. The resistance of a conductor decreases with decreasing temperature. With a further decrease in the temperature of the conductor, a complete decrease in resistance and the phenomenon of superconductivity are observed.
At a certain temperature (close to 0 oK) the resistance of the conductor drops sharply to zero. This phenomenon is called superconductivity. However, another phenomenon is also observed in superconductors - the Meissner effect. Conductors in a superconducting state exhibit unusual property. The magnetic field is completely displaced from the volume of the superconductor.
Displacement of a magnetic field by a superconductor.
A conductor in a superconducting state, in contrast to an ideal conductor, behaves like a diamagnetic material. The external magnetic field is displaced from the volume of the superconductor. Then if you place a magnet over a superconductor, the magnet hangs in the air.
The occurrence of this effect is due to the fact that when a superconductor is introduced into a magnetic field, eddy induction currents arise in it, the magnetic field of which completely compensates for the external field (as in any diamagnetic material). But the induced magnetic field itself also creates eddy currents, the direction of which is opposite to the induction currents in direction and equal in magnitude. As a result, there is no magnetic field or current in the volume of the superconductor. The volume of the superconductor is shielded by a thin near-surface layer - a skin layer - into the thickness of which (about 10-7-10-8 m) the magnetic field penetrates and in which its compensation occurs.
A- a normal conductor with non-zero resistance at any temperature (1) is introduced into a magnetic field. According to the law electromagnetic induction currents arise that resist the penetration of the magnetic field into the metal (2). However, if the resistance is non-zero, they quickly decay. The magnetic field penetrates a sample of normal metal and is almost uniform (3);
b- from normal condition at temperatures above T c there are two ways: First: when the temperature decreases, the sample goes into a superconducting state, then a magnetic field can be applied, which is pushed out of the sample. Second: first apply a magnetic field that penetrates the sample, and then lower the temperature, then the field will be pushed out during the transition. Turning off the magnetic field gives the same picture;
V- if there were no Meissner effect, the conductor without resistance would behave differently. When transitioning to a state without resistance in a magnetic field, it would maintain a magnetic field and would retain it even when the external magnetic field is removed. It would be possible to demagnetize such a magnet only by increasing the temperature. This behavior, however, has not been observed experimentally.