Positron states in YBa2Cu3O7-x

The authors present a series of calculations for positron states and lifetimes in perfect and defected YBa 2 Cu 3 O 7-x using an atomistic model. A simple relationship is found between the lifetime and the oxygen deficiency. The results suggest that the long-lived component resolved in lifetime spectra is associated with metal vacancies and/or metal-oxygen-vacancy complexes, while oxygen vacancies are found to be only shallow positron traps. The authors give an interpretation of positron lifetime experiments in terms of defects, oxygen-deficient domains and structural changes in the material.