Experimental and atomistic modelling study of ion irradiation damage in thin crystals of the TiO 2 polymorphs
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1124-Q04-09
Experimental and atomistic modelling study of ion irradiation damage in thin crystals of the TiO2 polymorphs G.R. Lumpkin1, K.L. Smith1, M.G. Blackford1, B.S. Thomas1, K.R. Whittle1, D.J. Attard1, N.J. Zaluzec2, and N.A. Marks3 1 ANSTO,
Private Mail Bag 1, Menai 2234, NSW, Australia
2 Argonne National Laboratory, 9700 South Cass Avenue, Argonne, 3 Curtin University of Technology, Perth, WA 6845, Australia
IL 60439, USA
ABSTRACT Thin crystals of rutile, brookite, and anatase were irradiated in-situ with 1.0 MeV Kr using the IVEM-TANDEM facility. Synthetic rutile and cassisterite (SnO2, rutile structure) remained crystalline up to 5 × 1015 ion cm-2 at 50 K. Natural brookite and anatase with low impurity levels became amorphous at 8.1 ± 1.8 × 1014 and 2.3 ± 0.2 × 1014 ions cm-2, respectively, at 50 K. Irradiation at higher temperature revealed Tc = 170 K for brookite and 242 K for anatase. Natural rutile with about 2 wt% impurities became amorphous at 9.4 ± 1.8 × 1014 ions cm-2 at 50 K and has a Tc = 207 K. The available data reveal both a structural effect in the polymorphs with low levels of chemical impurities and a chemical effect in natural rutile specimens containing up to about 1.7 wt% impurities. INTRODUCTION TiO2 compounds have a number of important industrial and technological applications, including use in pigments, photocatalysis, oxygen sensors, and thin film devices (e.g., antireflective coatings, waveguides, and optical amplifiers) [1]. TiO2 is also an important chemical component of polyphase and single-phase ceramic nuclear waste forms [2]. We recently tested the structure type criterion and other potential factors affecting susceptibility to amorphization using samples of the low-pressure TiO2 polymorphs rutile, brookite, and anatase [3,4]. In this paper, we summarize our initial studies of ion irradiation damage and atomistic modelling of synthetic rutile and natural brookite and anatase with low levels of chemical impurities. We also include new experimental results for natural cassiterite with low levels of chemical impurities and two natural rutile samples containing up to about 1.7 wt% of chemical impurities (mainly transition metals), new electron energy loss spectroscopy (EELS) results, and some additional atomistic modelling data. EXPERIMENTAL PROCEDURES AND RESULTS Samples were irradiated in situ at the IVEM-Tandem Facility at Argonne National Laboratory. TEM specimens were irradiated with 1.0 MeV Kr2+ ions in a Hitachi 300 keV electron microscope. All experiments were conducted at cryogenic temperatures (50-225 K) using a liquid He cooled sample holder with the electron beam turned off during the irradiations. Specimens were irradiated incrementally and observed in bright field and selected area
diffraction modes after each step. For those specimens that become amorphous, we determined the critical temperature for amorphization using non-linear least squares fitting procedures. The results of the irradiation experiments conducted at 50 K on the samples with low levels of c
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