Interpretation of radiation damage in platinum.— III. Migration modes and thermal conversion of self-interstitials

In previous papers (Parts I and II) it has been shown that self-interstitials in Pt may occur in two distinct configurations. In the present paper (Part III) it is demonstrated that the metastable configuration migrates one-dimensionally in Stage I, (k, it is of crowdion type), whereas the stable one undergoes free migration in three dimensions in Stage-III. Above 145 K the crowdion configuration becomes thermally unstable by overcoming the enthalpy barrier Hc c (≈ 0.2 eV) to the stable Stage-III configuration. These results are deduced from measurements of the average size of vacancy clusters in heavy ion bombarded Pt as a function of the irradiation temperature by means of transmission electron microscopy. The strength and the generality of this technique is demonstrated by relating the present results to those obtained on other metals, namely on Ni, Cu, Ag, and Au: Whereas self-interstitials in Ni, Cu, or Ag show essentially the same properties as Pt self-interstitials, the migration of crowdions in Au is suppressed, since their conversion enthalpy is smaller than their migration enthalpy. This explains peculiar features of irradiated Au, such as the absence of Stage IE.