The Strukturbericht designation D03 is bcc and correct. The same crystal structure of a ternary phase is L21. L12 is the structure of fcc Cu3Au (see J. H. Westbrook, Robert L. Fleischer (Hrsg.): Intermetallic Compounds: Principles and Applications. 2 Volume Set: Principles/Practice v. 1 & 2. John Wiley & Sons, 1994, ISBN 0-471-93453-4.)

G. Sauthoff

Strictly speaking the bcc-derivative D03 phase is not a bcc, but it has space group Fm3m. Nevertheless, considering the question, the above answer is ok.  You can find L12 phase also in ferrous alloys, e.g. Fe-Ga, Fe-Ge, it is ordered fcc-derivative phase with space group Pm3m. The L21 structure is applicable only for ternary alloys, it can be often observed in Heusler alloys.

Thanks for the explaination..

Sir, Fe3Al is binary and in literature it is refered as DO3 as well as L12. so I want to understand which one is correct..?

Please, note that designation DO3 does not exist! You mean D03 structure.

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doi: 10.1063/1.4840318