In this video, Dr Nick Strickland, a research scientist at IRL, describes the shift that has occurred in the superconductor field from using metal and alloy superconductors that need to be cooled to 4 K to new ceramic superconductors that operate at higher temperatures. By developing ceramic materials that show superconductive properties at temperatures above 77 K (the boiling point of nitrogen), Nick explains some of the economic benefits. This class of superconductor is called ‘high-temperature’, which is a relative term only.
Point of interest
How is liquid nitrogen made?
DR NICK STRICKLAND
Superconductivity is the absence of resistance or loss of all resistance. Resistance is a property that a normal metal has that means it heats up when you put a current through it, and superconductors don't have this property, so you can put as much current or you can put a lot of current through and not generate any heat.
The conventional low-temperature superconductors are metals or metal alloys. The first superconductor discovered was mercury – at very low temperatures close to absolute zero, which of course, it’s a solid, not a liquid. Subsequently, other metals were found to be superconductors, niobium perhaps the best known, and then alloys of niobium became even more useful, and these required to be cooled down to a temperature of liquid helium, which is very close to absolute zero.
The high-temperature superconductors, which can run at about minus 200 degrees Celsius and were discovered in the late 1980s, are actually composed of complex copper oxide materials, which you normally would not associate with a good conductor at all. The traditional low-temperature superconductors tend to be metal alloys. The high-temperature superconductors, being oxides, are brittle, they are not malleable, and so they are very difficult to deal with in terms of trying to form them into wires to put a current through them.