Structural mapping of intermetallic compounds and bond character

Abstract

The bond character of an intermetallic compound is expressed by two band parameters (the hybrid function H and gap reduction parameter S), which are available for crystal structure mapping of compounds. These parameters are constructed using Zunger's orbital electronegativities and the bond orbital model. It was shown that H and S correspond substantially to ionic and covalent band gaps in the one-gap model respectively. The bond character of an intermetallic compound is evaluated by the ionicity F i, which is expressed by the formula F i = H 2 (H 2 + 4S 2) . The ratio of H to S is the important parameter for determining the structural domain. Further, the two band parameters were used to determine the site preference of the alloying element in intermetallic compounds. The site preference of transition and post-transition metals in γ′-Ni 3Al and γ-TiAl determined from the parameter H S are in good agreement with previous experimental results, except for Nb in γ-TiAl. The good agreement indicates that the parameter H S can be used to predict the site preference of the alloying element in intermetallic compounds.