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Name: Unknown
Status: N/A
Age: N/A
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Country: N/A
Date: Around 1993


Question:
What are the materials most often used to achieve superconductivity?



Replies:
Well, the most important material for many years was liquid helium; just about any metal turns superconducting when it is cold enough. It is actually easier to list the exceptions - none of the noble metals (copper, silver, gold) do it, for example, at least to temperatures as low as can be measured. The materials "most often" used change with time. Basically, people try to use the best materials available, which depends on a whole lot of different properties, the most important of which being a high enough superconducting transition temperature. Of the old low-Tc superconductors, probably the most common were the Niobium compounds, particularly Niobium-Tin, because they can remain superconducting up to about 30 absolute degrees. Just 6 or 7 years, ago, that old 30 degree barrier was dramatically broken by experiments discovering that certain ceramic materials (nonmetallic or very poorly metallic, containing Oxygen, which was a surprise) could super conduct at up to 100 degrees and more. The record is now around 130 degrees. This means that liquid helium is not necessary to cool these new superconductors - you can get superconductivity with ordinary liquid nitrogen. The first good materials, still widely studied, consisted of a compound of Yttrium, Barium, Copper, and Oxygen. Lots of other combinations have been tried in the last few years, and it looks like the Copper-Oxygen layers in these systems are the essential element. But these new materials are not widely used yet. Just wait a few years!

A. Smith



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