Dislocation loop evolution in Kr-irradiated ThO2

LF He and TK Yao and K Bawane and MM Jin and C Jiang and X Liu and WY Chen and JM Mann and DH Hurley and J Gan and M Khafizov, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 105, 5419-5435 (2022).

DOI: 10.1111/jace.18478

The early stage of microstructural evolution of ThO2, under krypton irradiation at 600, 800, and 1000 degrees C, was investigated using in situ transmission electron microscopy (TEM). Dislocation loops grew faster, whereas their number density decreased with increasing irradiation temperature. Loop density was found to decrease with ion dose. Interstitial dislocation loops, including Frank loops with Burgers vector of a/3 < 111 & rang; and perfect loops with Burgers vector of a/2 < 110 & rang;, were determined by traditional TEM and atomic resolution- scanning TEM techniques. Atomistic and mesoscale level modeling are performed to interpret experimental observations. The migration energy barriers of defects in ThO2 were calculated using density-functional theory. The energetics of different dislocation loop types were studied using molecular dynamics simulations. Loop density and diameter were analyzed using a kinetic rate theory model that considers stoichiometric loop evolution. This analysis reveals that loop growth is governed by the mobility of cation interstitials, whereas loop nucleation is determined by the mobility of anion defects. Lastly, a rate theory model was used to extract the diffusion coefficients of thorium interstitials, oxygen interstitials, and vacancies.

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