Raveau and Michel

Prior to the events of 1986-87, a substantial effort in the solid state chemistry of simple and complex copper oxides had been established in France. As early as 1980, structural chemists at Caen, under the direction of Michel and Raveau, studied the synthesis and structure of several ternary, quaternary, and multinary Cu-O compounds. 

During this same period of time, Michel and Raveau reported (141) the synthesis of La3BasCu6014+y, a new compound having some close relationship to the perovskite structure. This compound was the precursor to a variety of different copper-oxide derivatives a more complete paper on its structure was published (142) in 1987, and the recent physical property measurements indicated (143) no superconductivity in either the quenched or oxygen-annealed phases. 

In passing, it should be noted that Michel and Raveau had carried out electrical measurements on several alkaline-earth substituted La2Cu04 compounds and presented (140) their experimental results in a comprehensive review during 1984. Their work, however, was primarily structural with a focus on electrical and magnetic properties above 50 K for this reason they missed observing the superconducting transition at 30 K. It is this author s belief that these Cu-O phases should be called the "Raveau-Michel" phases in much the same way as the molybdenum sulfide superconductors are called the "Chevrel" phases. 

A determined search for superconductivity in metallic oxides was initiated in mid-summer of 1983 at the IBM, Zurich Research Laboratories in Riischliken, Switzerland. This research effort was an extension of previous work (145) on oxides, namely, Sr1.xCaxTiOs, which exhibited some unusual structural and ferro-electric transitions (see Section 2.2a). During the summer of 1983, the superconductivity research was focussed on copper-oxide compounds. Muller had projected the need for mixed Cu2+/Cu3+ valence states, Jahn-Teller interactions (associated with Cu2+ ions), and the presence of room temperature metallic conductivity to generate good superconductor candidates. These researchers then became aware of the publication by Michel, Er-Rakho, and Raveau (146) entitled ... 

B. Raveau, C. Michel and M. Hervieu, Crystal chemistry of superconducting rare-earth cuprates 31... 

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