New Crystal Structure Map for Intermetallic Compounds

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New crystal structure maps were proposed based on the calculation of electronic structures by the discrete variational (DV)-Xalpha cluster method. Two electronic parameters were utilized in order to construct such a map for aluminides and silicides containing transition metals, M. The one was the bond order that is a measure of the covalent bond strength between M and Al(or Si) atoms. The other was d orbital energy level which correlated with the atomic size and electronegativity of elements. For example, structure maps pertinent to MAl, M_3Al, MAl_3, MSi, M_3Si, MSi_2 and M_5Si_3 were made using these two theoretical parameters. There was clear separation of crystal structures in every map. It was found that these new maps were more accurate in predicting the crystal structures of the compounds than any other structure maps so far developed (for example, the Pettifor map ).Furthermore, structure maps which are usable even for ternary compounds were constructed by taking into account the substitutional sites of third elements in binary compounds. Employing the maps for five intermetallic compounds, TiAl, Nb_3Al, NiAl, FeAl and MoSi_2, the possibility of changing their crystal structures was examined by the addition of third elements into binary compounds. It was concluded that these new structure maps were useful for the design and development of new intermetallic compounds.