Elastic properties of MFe3N (M=Ni, Pd, Pt) studied by ab initio calculations

Using ab initio calculations, we have studied the correlation between the electronic structure and elastic properties of MFe3N phases (M=Ni, Pd, Pt). These ternary nitrides possess a bulk-modulus-to-C44 ratio from 2.3 to 2.9, a rather unusual ratio for nitrides. This may be understood based on the electronic structure: Predominantly covalent-ionic Fe–N layers are interleaved with predominantly metallic Fe–M layers. We propose that the unusually large bulk-modulus-to-C44 ratio is a consequence of weak coupling between the Fe–N and Fe–M layers (giving rise to a low C44) as well as strong coupling within Fe–N layers (giving rise to a large bulk modulus).