| http://www.w3.org/ns/prov#value | - During 1987 and 1988, a number of families of high temperature superconductors have been discovered, with confirmed critical temperatures all the way to 162 K. These materials are usually ceramics containing copper (whose apparent valence state appears to be trivalent), an alkaline earth metal (Ca, Sr, or Ba) and a rare earth including Yttrium.
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