Defects and transport processes in beryllium

Intrinsic and substitutional defect formation and migration energies for beryllium metal have been predicted via atomic scale computer simulation and are discussed with respect to equilibrium and radiation damage processes. Schottky disorder was found to be the dominant intrinsic defect process, but its high energy implies only a small concentration of beryllium vacancies in the lattice. The anti-Schottky energy, being higher, implies that the intrinsic interstitial concentration will be still orders of magnitude lower. The energy barriers for migration of Be vacancies and interstitials are similar, at 0.72 and 0.64 eV respectively; both are essentially isotropic processes. Extrinsic defect properties have been calculated for hydrogen, helium, oxygen, iron, aluminium, carbon, magnesium and silicon. For example, helium has a large positive solution energy but preferentially occupies a beryllium vacancy site. Conversely, oxygen has a negative solution energy and is most stable as an interstitial species. Iron has a small negative solution energy, while aluminium and magnesium have high positive solution energies. The key intermetallics FeBe5 and FeAlBe4 have also been investigated.