The effect of Mo atoms in ternary nitrides with ηη-type structure

The effect of Mo atoms in ternary ηη-type nitrides, T3Mo3N and T2Mo4N (T = Fe, Co, Ni), has been investigated by atomistic simulation. The calculated lattice constants and atomic coordinates are in good agreement with experiments. Calculated results show that adding more Mo atoms makes the crystal energies of T2Mo4N decrease markedly, which indicates that Mo atoms can stabilize these nitrides. The Mo atoms prefer to occupy the 16d sites and avoid the 32e sites in T2Mo4N. The calculated elastic constants and bulk modulus are compared with the experimental and the density functional theory (DFT) results. Furthermore, in order to evaluate the thermodynamic contribution by Mo atoms, the phonon density of states, specific heat, and vibrational entropy of Fe3Mo3N and Fe2Mo4N are also investigated.