Influence of thermochemical properties on ion mixing of markers in Cu and β-Zr at 77 K with Kr

Abstract

Ion mixing of Nb, Ru, Ag, In, Sb, Hf, Pt, Au, and Bi markers in a Cu matrix and of Ti, Cr, Fe, Co, Ni, Cu, Hf, W, and Au markers in a β-Zr matrix has been studied by irradiation with 750 keV Kr+ ions of doses from 5 × 1015 to 2 × 1016/cm2= at 77 K. Cu and β-Zr have quite different atomic properties and impurities in them also behave quite differently. Thus, through a systematic investigation, the influence of parameters and mechanisms on ion mixing is clarified. The mixing was analyzed in situ, using 1.8 and 1.9 MeV He ion backscattering spectrometry. The overall mixing efficiency, Dt/φFD, is significantly higher in Cu than in β-Zr. This difference is explained in terms of the thermal spike mechanism in these matrices. In Cu, the mixing efficiencies correlate with impurity tracer diffusivities and impurity-vacancy binding energies for the marker atoms in Cu. Vacancies apparently play a major role during thermal spike mixing in Cu. In β-Zr, the markers that are likely to dissolve substitutionally in the matrix, have slightly higher mixing efficiencies than the markers that are likely to dissolve interstitially. The results are interpreted with the diffusion properties of these impurities in β-Zr.