A study was made of the radiation response of geikielite; an ilmenite-group oxide. Oriented single crystals were bombarded with 200keV Ar2+ or 400keV Xe2+ ions. Rutherford back-scattering spectrometry ion channelling was then used to characterize the resultant radiation damage. In the case of 200keV Ar2+ ion bombardment, the sample was held at 100K and a buried amorphous 55nm-thick layer formed beneath a 90nm-thick defective crystalline layer after exposure to a fluence of 2 x 1015/cm2. More detailed experiments used incremental 400keV Xe2+ ion bombardment and Rutherford back-scattering spectrometry ion channelling to determine the extent and rate of radiation damage at temperatures of 170, 300 and 470K. This showed that there was a strong temperature dependence of damage accumulation, and that the critical amorphization fluence increased from 2 x 1015 Xe2+/cm2 (170K) to 6 x 1015 Xe2+/cm2 (300K) to more than 2.5 x 1016 Xe2+/cm2 (470K). Damage appeared to accumulate in several stages. A rapid initial growth levelled out at an intermediate stage and was followed by an increase up to eventual saturation. At 170 and 300K, the damage fraction saturated at 100%, whereas saturation occurred at about 80% at 470K. Rutherford back-scattering spectrometry ion channelling data suggested the possible formation of a radiation-induced metastable phase, in the damaged region, which might be considered to be analogous to pressure-induced or temperature-induced phase transformations in other ilmenite-group oxides. The present results suggested that ionicity, composition and melting temperature could play important roles in the radiation response of ceramics; particularly with regard to determining the relative radiation tolerance of members of a solid-solution series.

J.N.Mitchell, N.Yu, K.E.Sickafus, M.A.Nastasi, K.J.McClellan: Philosophical Magazine A, 1998, 78[3], 713-25