Structural, electronic and magnetic properties of cementite-type Fe3X (X = B, C, N) by first-principles calculations

Using first-principles technique, the crystal structure of cementite-type Fe3N is predicted. The average magnetic moment (Ms) of cementite-type Fe3N is also predicted as 1.4929 μB/atom. The Ms of Fe3N is bigger than that of Fe3C, but smaller than that of Fe3B. Fe Ms between two different Fe sites in Fe3N are different (2.0541 and 2.0139 μB), which indicates that Fe Ms are sensitive to the local short-range order in the cementite-type crystal. The Ms of B, C and N are −0.3525, −0.2474 and −0.1102 μB/atom in Fe3X (X = B, C, N), respectively. The chemical bonds of Fe3X (X = B, C, N) take on metallicity, covalence, and ionicity. The ionicity of Fe3X (X = B, C, N) strengthens and the covalence of Fe–X weakens, going from Fe3B, Fe3C to Fe3N.

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