ABSTRACT
One of the most interesting features of the new oxide superconductors is that they are all non-stoichiometric oxides. Moreover, the superconductivity is closely correlated with the degree of non-stoichiometry. Superconductivity was first discovered in 1911. It is a low temperature phenomenon which was first thought to be limited to a number of metallic elements and alloys. The situation changed in 1987 when a number of complexes copper oxides were synthesized which could transform to the superconducting state above liquid nitrogen temperatures. The lower cost of cooling high temperature superconductors makes them attractive for the applications. The transition temperature does not vary across the composition range because the superconducting component never changes although the percentage of superconducting phase does alter. Oxygen is easily lost by heating the samples to temperatures of several hundred degrees. Thus, the tetragonal form of the compound has an extended composition range which is dependent on oxygen content and temperature.
