Supercheap superconductors

Superconductor is made from a cheap chemical

Published: Sunday 15 April 2001

diboride works as a superconductor at about -234 c, reveals research conducted at the Aoyama-Gakuin University in Japan. The material can be made easily from cheap laboratory chemicals. This could prove to be a turning point in the field of superconductivity. The temperature at which the magnesium and boron compound acts like a superconductor -- 39 kelvin or -234 c -- is almost twice that required for any previously studied materials.

This discovery is important because with the development of ceramic high-temperature superconductors, research on simple compounds had been abandoned. The findings of the Japanese scientists now put simple compounds back in the running. Though the new compound isn't the best superconductor known, scientists have hopes that with slight modification in their structure, they can greatly improve performance of the material (Nature , Vol 410, pg63)

The Dutch physicist, Heike Kamerlingh Onnes, discovered superconductivity in mercury in 1911. Similar behaviour has been found in approximately 25 other chemical elements, including lead, tin and thousands of other alloys and chemical compounds. All other materials that have been investigated to within fractions of a degree of absolute zero (0k or -273 c) show normal resistance to the flow of electric currents. Superconductivity is the complete disappearance of electrical resistance in various solids when they are cooled below a characteristic temperature. This temperature, called the transition temperature, varies for different materials, but is generally below 20 k (-253c). For instance, in mercury Onnes found the transition temperature to be -269 c .

Today, superconducting materials finds a variety of uses. They are very useful for making strong magnets, such as those used for magnetic resonance imaging in hospitals, or in experimental train systems that operate through magnetic levitation. The problem in the use of superconducting materials is the low transition temperature required. All this changed in the late 1980s with the development of high temperature superconductors which were superconducting above liquid nitrogen temperatures. Liquid nitrogen is very cheap and easy to make and store. These compounds were typically ceramics containing complex combinations of oxygen and two or more metals. The best of this modern generation superconducts worked at -139 c , but it could not carry large enough current for practical applications without being cooled to well below its critical temperature.

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