TOPOTACTIC REACTIONS OF SUPERCONDUCTING YBA2CU3O7 THIN-FILMS WITH WATER-VAPOR

The mechanism of the topotactic reaction of superconducting YBa2Cu3O7 thin films with water vapour is shown to be strongly influenced by the reaction kinetics. At elevated temperatures a quasi-continuous transi tion is observed while at lower temperatures a discontinuous transform ation occurs with two phase regions and the appearance of a new superc onducting metastable intermediate. The latter can be described as a se cond stage compound. Models are discussed - based primarily on diffrac tion and spectroscopic data - for the changes observed in structure an d stoichiometry in order to understand the complex reaction mechanism of this low temperature solid state process and the effects on the ele ctronic properties of the thin layer material.