A study was made of structural changes in spinel monocrystals after 400keV Xe2+ irradiation at 100K to a dose of 1016/cm2. The radiation-damaged layer was investigated by using cross-sectional transmission electron microscopy. It was found that the first-order Bragg reflections decreased in intensity with increasing dose, and eventually disappeared; thus indicating a transformation to a metastable crystalline state. Further irradiation resulted in the amorphization of the damaged layer. Because of the good radiation resistance of spinels, the present results suggested that transformation to the metastable state could be an important step in the amorphization process. Various models for the structure of the metastable phase were examined by calculating the diffraction patterns and comparing them with the electron diffraction data. The results indicated that a face-centered cubic O lattice, with cation interstitials, provided the best explanation for the observed structural changes.

R.Devanathan, K.E.Sickafus, N.Yu, M.Nastasi: Philosophical Magazine Letters, 1995, 72[3], 155-61