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Binary and ternary interstitial alloys I. The iron-nitrogen system: the structures of Fe4N and Fe2N
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1948
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Abstract The ς-iron nitride phase (Fe2N), the existence of which is confirmed, is prepared by passing ammonia over iron at temperatures not exceeding 450° C and under such conditions that the partial pressure of hydrogen is negligible. The positions of the nitrogen atoms in y'(Fe4N) and in ς are determined. y' is a ‘normal’ 12a6 interstitial structure, the cubic unit cell of which contains four iron atomsat 0 0 0, 1/2 1/2 0, 1/2 0 1/2, 0 1/2 1/2, and one nitrogen atom at 1/2 1/2 1/2; at 6.1 weight % N, a = 3.787 kX. ς has a distorted 12b6 structure. The unit cell, with dimensions a, 5.512; b, 4.820; c, 4.416 kX at 11.3 weight % N, contains eight iron atoms at 0 0 0, 1/2 0 0, 1/4 1/2 0, 3/4 1/2 0, 0 1/3 1/2, 1/2 1/3 1/2, 1/4 5/6 1/2, 3/4 5/6 1/2, and four nitrogen atoms at 1/4 1/6 1/4, 1/2 2/3 1/4, 3/4 1/6 3/4, 0 2/3 3/4. Both y' and ς are fully ordered interstitial alloys.