Irradiation Induced Effects at Interfaces in a Nanocrystalline Ceria Thin Film on a Si Substrate
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Irradiation Induced Effects at Interfaces in a Nanocrystalline Ceria Thin Film on a Si Substrate Philip D Edmondson,1,2,§ Neil P Young,1 Chad M Parish,2 Fereydoon Namavar,3 William J Weber,2,4 and Yanwen Zhang2,4 1 Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA 3 University of Nebraska Medical Center, Omaha, NE 68196, USA 4 Department of Materials Science and Technology, University of Tennessee, Knoxville, TN 37996, USA § Corresponding author: Philip Edmondson, [email protected] ABSTRACT Thin films of nanocrystalline ceria on a Si substrate have been irradiated with 3 MeV Au+ ions to fluences of up to 1x1016 ions cm-2, at temperatures ranging between 160 to 400 K. During the irradiation, a band of contrast is observed to form at the thin film/substrate interface. Analysis by scanning transmission electron microscopy in conjunction with energy dispersive and electron energy loss spectroscopy techniques revealed that this band of contrast was a cerium silicate amorphous phase, with an approximate Ce:Si:O ratio of 1:1:3. INTRODUCTION Ceramics are key materials in the nuclear industry, having applications as core structure materials, inert fuel matrices, potential waste forms for the long term sequestration of high level nuclear waste, novel clad for improved accident tolerance under loss of coolant accident (LOCA) conditions, and as non-radioactive surrogates in the study of defect behavior of fuels under irradiation [1-9]. Whilst the majority of research effort has been devoted to the radiation response of single crystal or relatively large grained polycrystals, there has been little effort in the response of nanocrystalline materials. Nanocrystalline materials are technologically interesting materials due to their ability to control and modify their bulk properties by varying the grain size [10-12] and have been suggested as a viable route towards radiation tolerance [13]. All of these benefits are in part due to the large number of unique grain boundary structures produced in the film [14, 15]. Ceria is typically used as a non-radioactive surrogate in studies of the behavior of defects under irradiation due to a similar behavior when compared with UO2 and PuO2 [4, 16, 17]. Ceria is thermodynamically stable in the cubic phase, however the phase stability relies quite heavily on the O/Ce ratio. Ceria retains the cubic phase when CeO2-x is 0
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