Cooled to very low temperatures, some materials experience a sudden transition where electrical resistance drops to zero and any magnetic fields are expelled. This phenomenon is called superconductivity. Superconductors have a host of applications including powerful electromagnets, fast digital circuits and sensitive magnetometers, but the very low temperatures needed make the applications more difficult and expensive.  Until the 1980s, no superconductors existed above . Then in 1986 two IBM researchers, Georg Bednorz and K. Alex Müller, found a ceramic material with a critical temperature of . This set off a frenzied search for higher critical temperatures.
A group led by Paul Chu at the University of Houston explored some materials made of yttrium, barium, copper and oxygen (YCBO) and were the first to obtain a critical temperature above the boiling point of liquid nitrogen. The YCBO samples had a mixture of black and green minerals, and although the researchers knew the average composition, they did not know the compositions of the two phases. In February 1987, Chu turned to Mao and Hazen, because they could determine the composition of small mineral grains in rocks. It took Mao and Hazen a week to determine the compositions; the black phase, which turned out to be the superconductor, was YBaCuO.
Mao and Hazen determined that the crystal structure of the superconducting phase was like that of perovskite, an important mineral in Earths mantle. Subsequently, Hazens group identified twelve more high-temperature oxide superconductors, all with perovskite structures, and worked on organic superconductors.