β Scribed by J.K. Hulm; C. Laverick
No coin nor oath required. For personal study only.
The workhorse of high field magnet technology was, and still is, Nb-Ti, a ductile alloy that could be made into wires. A second material of great promise, Nb3Sn, can support larger electric currents and remain superconducting in higher magnetic fields, but has found much less use because of its brittle nature. Other materials have found specialized uses, for example, pure niobium in RF cavities and NbN in electronics.
Recently, new materials have been discovered that have substantially higher upper critical temperatures, Tc: designated high temperature superconductors (HTSCs), they still become superconductors at very low temperatures, but at temperatures almost five times higher than Nb3Sn. In January 1986 Bednorz and MLiller at the IBM Laboratory in ZLirich, searching for superconductivity in previously unexplored materials determined thatthe ceramic La Ba CuO oxide became superconducting at temperatures over 30 K.
Spurred on by this unexpected discovery, scientists throughout the world have since found materials with unexpectedly high TcS. The highest value achieved to date that has been independently confirmed is that achieved by Chu and colleagues at the University of Houston working with Wu and co-workers at the University of Alabama; about 98 K. At this temperature liquid nitrogen (which boils at 77 K atmospheric pressure and is much cheaper than liquid helium) can be used for cooling.
Even before the constituents of Chu's material were known, independent discoveries of the superconducting behaviour of these compounds were also made in China and Japan a few days later. The rapid dissemination of scientific results has occurred mainly through word of mouth, preprints, press releases and even television news programmes, reflecting the close-knit global community of scientific endeavour and the intense interest of policy makers, the news media and the public at large. International competition in this field is intense as the leading industrialized countries strive to determine what the technological and commercial prospects for the new materials might be.
A large number of the so-called high temperature superconductors, are now known to exist, all of them variations of two basic types (40 and 90 K, or 1-2 3 materials). Those with T c > 77 K are based on only one structure, with copper and oxygen a constant feature. There have been many preliminary reports of higher temperature superconductors but at present there is no consensus as to their validity. Room temperature superconductivity (T c > 400 K) would make possible
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