Structural mapping of intermetallic compounds and bond character

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 Zungerʹs 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 Fi, which is expressed by the formula Fi = H2(H2 + 4S2). 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′-Ni3Al and γ-TiAl determined from the parameter HS are in good agreement with previous experimental results, except for Nb in γ-TiAl. The good agreement indicates that the parameter HS can be used to predict the site preference of the alloying element in intermetallic compounds.