Superconductivity, discovered in 1911, is defined as the property at and below a certain critical temperature of some materials where the electrical resistance goes to zero ohms (0 Ω) due to unrestricted movement of electrons. An attendant expulsion of magnetic fields is what causes the familiar floating of a magnet above a superconductor (the Meissner effect).
All materials are superconductors at absolute zero (0K). Cooling to absolute zero is impossible due to quantum physics effects, and getting very close to it (within a couple degrees Kelvin) is very difficult. The goal is to create high temperature superconductor (HTS) materials (generally defined as being superconductive at a temperature above that of liquid nitrogen [77 K]) that can operate at or near room temperature. Use of superconducting materials in electrical machinery and transmission lines would mean significant savings in power generation requirements because all supplied power would be converted to useful work. At this point in time there have been test cases of nitrogen-cooled superconducting cables for commercial AC power transmission, but the cost benefit is negative. As of 2015, the highest temperature superconductor compound was mercury barium calcium copper oxide (HgBa2Ca2Cu3O8) at around 133 K.
The table of superconductivity values below are pulled from Reference Data for Radio Engineers, 1995, Sams Publishing. Please verify accuracy with a second source.
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Posted July 16, 2018