Oxide Superconductors: A Chemist's View

ABSTRACTThe brief history of oxide superconductors is presented and discussed in terms of structure, bonding and property interrelationships. The perovskite structure has been very prominent in the history of oxide superconductors, including the recently discovered copper oxide based superconductors. However, an alternate description of the high Tc superconductors in terms of sheets, chains and sticks may be more useful. Although chains and orthorhombic symmetry in RBa2Cu3O7 phases favor high Tc superconductivity, orthorhombic symmetry is not required to have well developed chains and reasonably high Tc (e.g ∼60 K). Furthermore, highly disordered LaBa2Cu3O7 and YBa2Cu3O6.7 phases are not superconducting even though they are weakly orthorhombic. Superconducting RBa2CueO6+x phases are prepared by oxygen intercalation of a semiconducting phase with a low x value; intercalation phases are not normally expected to be thermodynamically stable. A mechanism for superconductivity in oxides is presented based on disproportionation reactions such as 2CuII → CuI + CuIII and 2BiIV → BiIII + Biv.