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.

We have investigated the elastic properties of nanolayered ${\mathrm{M}}_2\mathrm{AC}$, with $\mathrm{M}=\mathrm{Ti}$, Zr, Hf, V, Nb, Ta, Cr, Mo, W and $\mathrm{A}=\mathrm{Al}$, Ga, Ge, Sn, by ab initio calculations. We suggest that ${\mathrm{M}}_2\mathrm{AC}$ can be classified into two groups: One where the bulk modulus of the binary MC is conserved and another group where the bulk modulus is decreased. This classification can be understood in terms of coupling between MC and A layers, which is defined by the valence electron population. These results may have implications for the understanding of properties and the performance of this class of solids.

We have synthesized Ta thin films on Si substrates placed along a wall of a 2-cm-deep and 1-cm-wide trench, using both a mostly neutral Ta flux by conventional dc magnetron sputtering (dcMS) and a mostly ionized Ta flux by high-power pulsed magnetron sputtering (HPPMS). Structure of the grown films was evaluated by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The Ta thin film grown by HPPMS has a smooth surface and a dense crystalline structure with grains oriented perpendicular to the substrate surface, whereas the film grown by dcMS exhibits a rough surface, pores between the grains, and an inclined columnar structure. The improved homogeneity achieved by HPPMS is a direct consequence of the high ion fraction of sputtered species.

${\mathrm{Ti}}_{1-x}{\mathrm{Al}}_x\mathrm{N}$ films and/or their alloys are employed in many industrial applications due to their excellent mechanical and thermal properties. Synthesized by plasma-assisted vapor deposition, ${\mathrm{Ti}}_{1-x}{\mathrm{Al}}_x\mathrm{N}$ is reported to crystallize in the cubic NaCl $\left(c\right)$ structure for AlN mole fractions below 0.4–0.91, whereas at larger Al contents the hexagonal ZnS-wurtzite $\left(w\right)$ structure is observed. Here we use ab initio calculations to analyze the effect of composition and Al distribution on the metal sublattice on phase stability, structure, and elastic properties of $c\text{-}{\mathrm{Ti}}_{1-x}{\mathrm{Al}}_x\mathrm{N}$ and $w\text{-}{\mathrm{Ti}}_{1-x}{\mathrm{Al}}_x\mathrm{N}$ . We show that the phase stability of supersaturated $c\text{-}{\mathrm{Ti}}_{1-x}{\mathrm{Al}}_x\mathrm{N}$ not only depends on the chemical composition but also on the Al distribution of the metal sublattice. An increase of the metastable solubility limit of AlN in $c\text{-}{\mathrm{Ti}}_{1-x}{\mathrm{Al}}_x\mathrm{N}$ from 0.64 to 0.74 is obtained by decreasing the number of Ti–Al bonds. This can be understood by considering the Al distribution induced changes of the electronic structure, bond energy, and configurational entropy. This may in part explain the large variation of the metastable solubility limit reported in the literature.

During annealing, metastable NaCl-structured $\left(c\right)$ ${\mathrm{Ti}}_{1-x}{\mathrm{Al}}_x\mathrm{N}$ films initially exhibit spinodal decomposition which results in age hardening. Based on ab initio calculations, we show that the chemical requirement for spinodal decomposition in the quasibinary $c\text{‐}\mathrm{Ti}\mathrm{N}–c\text{‐}\mathrm{Al}\mathrm{N}$ system is fulfilled over a wide composition and temperature range. The enthalpy change for the decomposition of $c\text{‐}{\mathrm{Ti}}_{0.34}{\mathrm{Al}}_{0.66}\mathrm{N}$ is $\sim 26.4\mathrm{kJ}{\mathrm{mol}}^{-1}$ , which is in good agreement with previously reported experiments. The obtained results enable materials design of ${\mathrm{Ti}}_{1-x}{\mathrm{Al}}_x\mathrm{N}$ -based coating systems for high-temperature applications.