Theoretical investigation of the bonding and elastic properties of nanolayered ternary nitrides

We have investigated the chemical bonding and the elastic properties of nanolayered ${\mathrm{M}}_{2}\mathrm{A}\mathrm{N}$, where $\mathrm{M}=\mathrm{Ti}$, Zr, Hf, V, Nb, Ta, Cr, Mo, and W and $\mathrm{A}=\mathrm{Al}$, Ga, and Ge, by ab initio calculations. The bulk modulus of ${\mathrm{M}}_{2}\mathrm{A}\mathrm{N}$ increases by a factor of 1.8 as the valence electron concentration increases in the range calculated. This can be understood by filling the M $d--\mathrm{N}$ $2p$ hybridized states. Furthermore, as the valence electron concentration is increased, the coupling between MN and A layers is weakened. These findings are important since the here-investigated nitrides exhibit the bulk-modulus-to-${c}_{44}$ ratio ranging from 1.2 to 8.0, exceeding even hexagonal BN. We hope that this work will inspire future experimental research on these so far close to uninvestigated ternary nitrides.

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