This study aims at understanding the anisotropy of the electronic properties of ${\text{Ti}}_2\text{AlN}$ at the nanometer scale. The dielectric response of ${\text{Ti}}_2\text{AlN}$ single grains was recorded in a transmission electron microscope for the [100] and [001] orientations using high-resolution electron energy-loss spectroscopy. The experimental results are interpreted using ab initio calculations based on the density functional theory. The two components of ${\text{Ti}}_2\text{AlN}$ dielectric tensor, corresponding to the response within the basal planes of the hexagonal structure and along its $c$ axis were computed within the random phase approximation. The results, in good agreement with experiments, show strong anisotropy. Local field effects (LFE), induced by the electronic density inhomogeneities, strongly modify the loss function along the [001] direction, which is dominated by a plasmon, a behavior very similar to the one obtained for pure metals. The dielectric response within the basal plane of the hexagonal structure, more complex, exhibits a plasmonlike behavior together with an interband transition. This interband transition is identified as being characteristic of the N-Ti bonds within the $\left[{\text{Ti}}_6\text{N}\right]$ octahedra. This study emphasizes the importance of LFE in the response of ${\text{Ti}}_2\text{AlN}$ to an electromagnetic perturbation.

• Received 5 October 2009

DOI:https://doi.org/10.1103/PhysRevB.81.035109