Highlights

Electron Energy Loss Spectroscopy Measurements of Amorphization of Polymorphs of TiO₂ Induced by Ion Irradiation

Scientific Achievement

Crystalline ceramic waste form materials have long been candidates for immobilization of high level radioactive waste.  Over the lifetime of their use the initial crystalline phases undergo alpha irradiation from the incorporated transuranics and slowly decay from their initial crystalline state to a fully amorphized structure.  This process of "vitrification" has long been studied, using combined in-situ ion irradiation and electron microscopy and a large family of complex oxides has been characterized.  Two important parameters established in such studies are: the critical full amorphization dose, Dc, at a particular temperature and the critical temperature above which a material remains crystalline, Tc.  In intermediate irradiations, (D < Dc) the degree of amorphization is difficult to establish, in this study we report on the preliminary use of Electron Energy Loss Spectroscopy (EELS) measurement of the changes in the Electron Energy Near Edge Structure (ELNES) of polymorphs of TiO₂ with irradiation dose as a means of determining the intermediate state.

Significance

The principle method used to study vitrication during ion irradiation experiments has nearly always been electron diffraction, however, while diffraction does determine the end point of the amorphization process, quantification  of intermediate states is at best tenuous.  Using multiple linear least squares fitting of starting and ending state NES for the Ti L shell, we are able to demonstrate that the amorphization process proceeds non-linearly in both rutile and anatase polymorphs of TiO₂.  This development now provides us with an additional tool for studying the vitrification process during irradiation.

Performers

N. J. Zaluzec (Argonne-EMC); K. L. Smith, G. R. Lumpkin, M. G. Blackford, K. R. Whittle (ANSTO)