Following Bednorz and Müller's work, in 1987 Jim Ashburn (at the University of Alabama in Huntsville), along with Chu Ching-wu (at the University of Houston), Maw-Kuen Wu, and C.J. Torng, discovered that YBCO has a superconducting transition critical temperature ("T"c, which must not be confused with the Curie temperature) of 93 K. The first samples were Y1.2Ba0.8CuO4; but this was an average composition for two phases, a black and a green one. To identify the phases, Chu turned to Dave Mao and Robert Hazen at the Geophysical Laboratory in the Carnegie Institution of Washington. They found that the black one (which turned out to be the superconductor) had the composition YBa2Cu3O7−δ. The article reporting this material led to rapid discovery of several new high-temperature superconducting materials, ushering in a new era in material science and chemistry.