Yttrium Barium Copper Oxide - History

History

In April 1986 (seventy-five years after the discovery of superconductivity in 1911), Georg Bednorz and Karl Müller, working at IBM in Zurich, discovered that certain semiconducting oxides became superconducting at 35 K, then considered a relatively high temperature. In particular, the lanthanum barium copper oxides, an oxygen deficient perovskite-related material, proved promising. In 1987, Bednorz and Müller were jointly awarded the Nobel Prize in Physics for this work.

Building on that, M.K. 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 (see superconductor page for info), discovered YBCO has a T_c of 93 K. (The first samples were Y_1.2Ba_0.8CuO₄.) 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 liquid nitrogen. All materials developed before 1986 became superconducting only at temperatures near the boiling points of liquid helium (T_b = 4.2 K) or liquid hydrogen (T_b = 20.28 K) — the highest being Nb₃Ge at 23 K. The significance of the discovery of YBCO is the much lower cost of the refrigerant used to cool the material to below the critical temperature.