Simulation of Inert Gas Interstitial Atoms in Tungsten
Computer simulation was used to investigate the equilibrium positions assumed by interstitial inert gas atoms in a tungsten crystal. Light atoms, He and Ne, occupy positions near the octahedral void. As the foreign atom mass increases the equilibrium position moves along the <110> direction from the void toward the split-interstitial position which has previously been associated with the self-interstitial in the bcc crystal. The preliminary studies were carried out in a perfect (cold) lattice. Subsequent studies of Ar in a warmed lattice indicate that the interstitial sites are not well localized. The foreign atom occupies a shallow trough-well lying along the <110> axis near the tetrahedral void position. The lattice does not force the interstitial atom toward a predetermined site, rather the atom moves, but the surrounding lattice atoms also shift their positions to accommodate to its final position. The result is almost a local liquifaction effect; as contrasted to a distorted lattice which retains some symmetry. Presumably this behavior occurs because the bcc lattice is not close packed. The presence of a nearby surface affects the stability of the foreign atom in the crystal. Interstitial atoms placed in the first two (010) atomic layers did not reach stable equilibrium positions. Reproducible sites were defined for all of the inert gas atoms in the third atomic layer. In the third atomic layer of a cold lattice the interstitial Ar atom binding energy lies between 0.04 and 0.02 eV.
KeywordsEquilibrium Position Final Position Interstitial Atom Lattice Atom Foreign Atom
Unable to display preview. Download preview PDF.