recorded critical temperature was about 23 K in a niobium-germanium compound
(NbsGe) whose superconductivity was discovered in the early 1970s. In 1986 Bednorz
and Miiller, at IBM Research Laboratories in Zurich, discovered that a copper
oxide-based ceramic-type compound La-Ba-Cu-O, which normally has high resistivity,
becomes superconducting when cooled below 35 K. Following this Nobel
prize-winning discovery, a variety of copper oxide-based compounds (called cuprate
ceramics) have been synthesized and studied. In 1987 it was found that yttrium barium
copper oxide (Y-Ba-Cu-O) becomes superconducting at a critical temperature
of 95 K, which is above the boiling point of nitrogen (77 K). This discovery was particularly
significant because liquid nitrogen is an inexpensive cryogent that is readily
liquified and easy to use compared with cryogent liquids that had to be used in the