In 1913, lead was found to superconduct at 7 K, and in 1941 niobium nitride was found to superconduct at 16 K. The next important step in understanding superconductivity occurred in 1933, when Walther Meissner and Robert Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon that has come to be known as the Meissner effect.
This, along with the fact that the oxide material is also easy to make and inexpensive, played a major role in giving research in superconductivity an added boost.
Another group, at the University of California at Berkeley, reported the appearance of superconductivity at 292 K, or 66° F. [19° C.], in a material they were working on, but they were not able to repeat the result.
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Maglevs —magnetically-levitated trains— with speeds up to 300 miles an hour [480 km/ h] may be made practicable by lightweight superconducting magnets.
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Experimental power transformers in the 500‐to‐1,000 kVA range have been built with liquid nitrogen or helium cooled superconducting windings, which eliminates winding losses without affecting core losses.
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In Russia, Kapitsa began a series of experiments to study liquid helium, leading to the discovery in 1937 of its superfluidity (not to be confused with superconductivity).
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Liquid helium is used in cryogenics (its largest single use, absorbing about a quarter of production), particularly in the cooling of superconducting magnets, with the main commercial application being in MRI scanners.
To complicate matters further, scientists are not sure if the superconducting materials are capable of carrying the large electric currents or magnetic fields that many applications call for.
In 1962, the first commercial superconducting wire, a niobium-titanium alloy, was developed by researchers at Westinghouse, allowing the construction of the first practical superconducting magnets.
However, the extremely low temperature, called the transition, or critical, temperature, at which the material became superconducting was a severe handicap.
Principal research instruments include a nuclotron superconductive particle accelerator (particle energy: 7 GeV), three isochronic cyclotrons (120, 145, 650 MeV), a phasotron (680 MeV) and a synchrophasotron (4 GeV).
By early 1986 they had achieved the first major advance in years, superconductivity at 35 K, or -396° F. [-238° C.], using a compound consisting of barium, lanthanum, copper, and oxygen.
Chu of the University of Houston discovered superconductivity in a material at a record high of 93 K, or -292° F. [-180° C.], by replacing the lanthanum in Müller’s mixture with yttrium, another of the so-called rare earth elements.
As recently as 1973, the best that had been found was a certain metallic alloy that became superconducting at 23 K, or -418° F. [-250° C.], still an impractically low temperature.