ABSTRACT
Considerable effort has been devoted to characterizing the properties of the recently discovered copper-oxide superconductors.1-7 However, there have been relatively few systematic studies8-10 reporting on the electrical transport properties of nonsuperconducting copperoxide perovskites, despite the fact that nonsuperconducting materials comprise a much larger phase space than the superconducting specimens. Relatively minor changes in oxygen content are sufficient to convert a superconducting "123" compound into a nonsuperconductor. For example, YBa2Cu3O6.9 is a superconductor, whereas YBa2Cu3O6.4 is not. We suggest that the term "incipient superconductor" be applied to compounds such as YBa2Cu3O6.4 and La2CuO4, since simply annealing the former in oxygen or doping the latter with an alkaline earth is sufficient to convert the respective compound into a high Tc superconductor.
