Internal oxidation of 5sp impurities in noble metals

Abstract

The internal oxidation of ion-implanted radioactive¹¹⁹In,¹¹⁹Cd, and¹¹⁹Sb in high-purity (5N) copper, silver, and gold single crystals has been investigated. The formation of the impurity-oxygen defect structures was monitored by Mössbauer emission spectroscopy on the 24 keVγ-radiation from the daughter¹¹⁹Sn after theΒ-decay of the implanted radioactive isotopes. Molecule-like complexes are formed consisting of the implanted impurity and several oxygen atoms. The various Mössbauer parameters (isomer shift, quadrupole splitting, and Debye temperature) enable a distinction between different Sn-IV and Sn-II complexes, as well as between substitutional and vacancy-associated Sn atoms, which result from the ion implantations. The evolution of oxygen complexes with temperature during isochronal annealing was studied in the temperature range 300–1000 K. The formation (around 500 K) and the disintegration (around 900 K) of the complexes, in' silver in particular, are explained on the basis of diffusion properties of oxygen. A comparison of results from oxidations due to either thermal diffusion of oxygen or due to recoil implantations from a surface-oxide layer indicates that Sn-IV complexes are invariably formed in the first case, whereas in the latter case, a mixture of Sn-IV and Sn-II complexes is formed. Relations of the present results to similar results from PAC measurements on¹¹¹Cd in silver and from Mössbauer experiments on AgSn alloys are discussed.