ATOMIC SELF-DIFFUSION IN QUASICRYSTALS.pdf

ATOMIC SELF-DIFFUSION IN QUASICRYSTALSFRANZ GAHLER and JOHANNES ROTHLaboratory of Atomic and Solid State PhysicsCornell University, Ithaca, NY 14853-2501, U.S.A.ABSTRACTA molecular dynamics study on atomic self-diusion in Frank-Kasper type do-decagonal quasicrystals is presented. It is found that the quasicrystal-specic ipmechanism for atomic diusion, predicted by Kalugin and Katz, indeed occurs inthis system. However, in order to be eective, this mechanism needs to be catalyzedby other defects, such as half-vacancies. For this reason, ip diusion is dicult todistinguish from standard vacancy diusion.1. IntroductionThere has recently been much interest in atomic self-diusion in quasicrystals,mostly triggered by a paper by Kalugin and Katz1, where a diusion mechanismspecic to quasicrystals was proposed. The elementary process in this ip mech-anism consists of certain quasicrystal-specic rearrangements of atoms, where theinitial and nal congurations are energetically almost degenerate. In quasicrys-tals which are decorations of quasiperiodic tilings, the ip mechanism consists of areshuing of certain local tile congurations, along with their decorations1.Flip diusion has so far been studied in pure tiling models, without botheringabout a specic atomic decoration of the tilings2;3. While such an approach mayprove that elementary ip processes do add up to diusive behaviour, the physicalfeasibility of the ip mechanism and the magnitude of ip diusion remain much lesscertain. In particular, activation energies of elementary ips cannot be estimatedwithout a concrete atomic structure, and in a reshuing of tiles atoms may haveto move only much smaller distances than the vertices of the tiles. Those questionscannot be studied without having a specic atomic structure in mind.We therefore propose to study the feasibility of ip diusion in a concrete atomicmodel quasicrystal, by means of molecular dynamics (MD) simulations. For such asimulation, not