Stability and diffusion of Hg implanted YBa2Cu3O6+x

The radioactive isotope Hg-197m was implanted at 60 keV with low fluences (10(13) ions/cm(2)) into YBa2Cu3O6+x (YBCO) superconducting thin films at ISOLDE/CERN. We report on the Hg dynamics and stability inside the YBCO lattice as a function of annealing temperature up to 890 K in a vacuum or O-2 atmosphere. The perturbed angular correlation (PAC) technique was used for probing the Hg behavior at the atomic scale, while by monitoring the sample's activity in situ the Hg outdiffusion was studied. We found that Hg ions occupy unique lattice sites and that Hg should be bound to two apical oxygens. Hg diffusion occurs only for annealing temperatures above 653 K, in vacuum. The Hg migration energy was estimated to be E-M=1.58 +/- 0.15 eV. (C) 1999 Elsevier Science B.V. All rights reserved.