Formation, migration, and clustering energies of interstitial He in α-quartz and β-cristobalite

Precipitation of implanted helium (He) is detrimental to many nuclear materials. A solid in which implanted He does not precipitate, but rather remains in solution and diffuses readily is potentially of interest for applications requiring resistance to He-induced damage. We use density functional theory (DFT) calculations to examine He interstitial formation, migration, and clustering energies in two SiO2 polymorphs: alpha-quartz and beta-cristobalite. Our findings show greater He solubility and mobility in the latter than in the former. This difference appears to be due primarily to the unlike atomic-level structures of alpha-quartz and beta-cristobalite, rather than their differing densities. Our findings also suggest that He is unlikely to cluster in either material. The behavior of He in alpha-quartz and beta-cristobalite, and similar forms of silica make them promising materials for further investigation for potential use in applications requiring resistance to He-induced damage. (C) 2016 Elsevier B.V. All rights reserved.