Internal oxidation of In and Cd impurities in silver

Abstract

Internal oxidation of indium and cadmium implanted in silver single crystals has been studied by time-differential perturbed angular correlation (TDPAC) as well as by nuclear-reaction analysis (NRA) with the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$(p,α${)}^{15}$N reaction. Oxidation at 550 K results in the formation of the so-called indium-oxygen 2a complexes, as observed with ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ TDPAC. The main axis of the axially symmetric electric field gradient (EFG) of this complex is pointing in a 〈100〉 crystallographic direction. The NRA measurements show that two oxygen atoms are trapped, at near-interstitial sites, by each indium atom. After subsequent annealing above 700 K, the geometry of the 2a complexes has changed and the so-called 2b complexes are formed. The asymmetry parameter of the EFG equals η=0.8(2) with the z and y axes pointing in 〈100〉 directions. Again, two oxygen atoms are trapped at each indium atom, but with 40% of the oxygen atoms shifted into near-substitutional sites. The other 60% are located at ‘‘random’’ sites. This change in electronic and geometric structure occurring at the 2a→2b transition might be due to trapping of thermally activated vacancies by the 2a complexes. Subsequent annealing above 873 K results in the agglomeration of the 2b complexes into ${\mathrm{In}}_2$ ${\mathrm{O}}_3$ precipitates. Annealing at 1050 K leads to dissociation of these precipitates. Internal oxidation of very dilute cadmium in silver single crystals below 700 K leads to the formation of cadmium-oxygen complexes with the TDPAC characteristics of the ${\mathrm{InO}}_2$ 2a complexes.