No abstract

By use of the self-consistent field Xα scattered-wave method, the electronic structure was calculated for two models of the Ti6Al12X (X=Al, Cr, or Mn) cluster for the tetragonal DO22 crystal strcuture as well as the Ti4Al14X (X=Al, Cr, or Mn) cluster for the cubic L12 crystal structure in Al3Ti-base intermetallic compounds for contrast. The results are presented for density of states and one-electron properties, such as the relative binding tendency between the atom and the model cluster and the hybrid bonding tendency between the atoms introduced by us. Comparisons are made among the three models of the Ti6Al12X cluster, among those of the Ti4Al14X cluster, and between Ti6Al12X and Ti4Al14X clusters. The effect of the Cr or Mn atom on the physical properties of Al3Ti-base intermetallic compounds is analyzed. The calculations indicate that the addition of the Cr or Mn atom weakens the relative binding tendency between the Ti2 atom and the Ti6Al12X cluster and intensifies that between the Ti1 atom and the Ti4Al14X cluster. Thus the addition of the Cr or Mn atom may promote crystal structure transformation from DO22 to L12 in Al3Ti-base intermetallic compounds. Comparison of the density of states between the Ti6Al12X and Ti4Al14X clusters shows that the stable crystal structure for a given compound is the one in which the Fermi level EF lies in or comes near a minimum in the density of states. The calculation also shows that the Cr or Mn atom strengthens the hybrid bonding tendency between the central atom and the host atoms for the Ti6Al12X and Ti4Al14X clusters and thereby may lead to the constriction of the lattice constant of Al3Ti-base intermetallic compounds. The results also show that the addition of the Cr or Mn atom provides more d electrons to strengthen the p-d and d-d directional bondings for the Ti6Al12X and the Ti4Al14X clusters. Thus, Al3Ti-base intermetallic compounds with the addition of the Cr or Mn atom still remain brittle.