Semiconducting Al-transition-metal alloys

Marian Krajci, Juergen Hafner

    Veröffentlichungen: Beitrag in BuchBeitrag in Konferenzband

    Abstract

    Alloys composed by metallic elements are naturally expected to be metallic too. However, in intermetallic compounds formed by transition-metals (TM) and Al, in some cases a special Al-TM ordering can lead to the formation of a deep pseudogap or even a band-gap in the electronic spectrum at or close to the Fermi-level resulting in semimetallic and eventually even semiconducting behavior. A prototype of such semiconducting or semimetallic compound is the Al2Ru alloy with the orthorhombic C54 structure. Less well known is that also some quasicrystals which are structurally very complex systems can show similar semiconducting properties. An example of a such system is the icosahedral AlPdRe alloy. On the basis of ab-initio electronic structure calculations we systematically studied semiconductivity in some crystalline and quasicrystalline phases. We found that the semiconducting behavior is accompanied with a formation of chemical bonds between aluminum and transition-metal atoms with a high degree of covalency. The bonds form a network with a special Al-TM ordering. Any deviation from this ordering, for instance the existence of substitutional defects, leads to formation of localized states in the gap. We investigated the mechanism of the band-gap formation. The hybridization plays here an important role. It can be responsible for a formation of a deep minimum in the density of states but for a true band-gap formation the hybridization alone is not sufficient. A breaking of symmetry of the crystal structure is also very essential. The mechanism seems to be analogous to the Peierls mechanism of the band-gap formation. Based on our ab-initio calculations, we predict existence of many novel crystalline and quasicrystalline alloys with true semiconducting behavior.
    OriginalspracheEnglisch
    TitelScience of Complex Alloy Phases Symposium - TMS 2005 Annual Meeting
    Seiten251-280
    Seitenumfang30
    PublikationsstatusVeröffentlicht - 2005

    Publikationsreihe

    ReiheTMS annual meeting

    ÖFOS 2012

    • 1030 Physik, Astronomie

    Zitationsweisen