Yttrium barium copper oxide
Yttrium barium copper oxide, often abbreviated YBCO, is a chemical compound with the formula YBa2Cu3O7. This material, a famous "high-temperature superconductor", achieved prominence because it was the first material to achieve superconductivity above the boiling point of nitrogen.
Seventy-five years after the discovery of superconductivity, Georg Bednorz and Alexander Müller, working at IBM in Zurich Switzerland, discovered that certain semiconducting oxides became superconducting at the then relatively high temperature of 35 K. In particular, the lanthanum barium copper oxides, an oxygen deficient perovskite-related material proved particularly promising.
Building on the motif discovered by Bednorz and Müller, Maw-Kuen Wu and his graduate students, Ashburn and Torng at the University of Alabama in Huntsville in 1987 and Paul Chu and his students at the University of Houston in 1987, discovered YBCO. Their work led to a rapid succession of new high temperature superconducting materials, ushering in a new era in material science and chemistry.
YBCO was the first material to become superconducting above 77 K, the boiling point of nitrogen. All materials developed before YBCO became superconducting only at temperatures near the boiling points of liquid helium or liquid hydrogen (Tb = 20.1 K). The significance of the discovery of YBCO is the breakthrough in the refrigerant used to cool the material to below the critical temperature.