Experimental and first-principles investigation of the electronic structure anisotropy ofCr2AlC

Abstract

The anisotropy of the electronic structure of the $\mathit{MAX}$ phase ${\mathrm{Cr}}_{2}\mathrm{AlC}$ has been investigated by electron-energy-loss spectroscopy (EELS) at the C $K$ edge, and x-ray-absorption spectroscopy (XAS) at the Al $K$, Cr ${L}_{2,3}$, and Cr $K$ edges. The experimental spectra were interpreted using either a multiple-scattering approach or a full-potential band-structure method. The anisotropy is found to be small around C atoms because of the rather isotropic nature of the octahedral site, and of the averaging of the empty C $p$ states probed by EELS at the C $K$ edge. In turn, a pronounced anisotropy of the charge distribution around Al atoms is evidenced from polarized XAS measurements performed on textured ${\mathrm{Cr}}_{2}\mathrm{AlC}$ sputtered thin films. From the analysis of the XAS data using the multiple-scattering feff code, it is demonstrated that the probed thin film is constituted of $70%$ (0001) and $30%$ $(10\overline{1}3)$ grains oriented parallel to the film surface. A decomposition of the calculated spectrum in coordination shells allows for the ability to connect XAS fine structures to the ${\mathrm{Cr}}_{2}\mathrm{AlC}$ structure. Combining high-resolution data with up-to-date multiple-scattering calculations, it is shown that the crystalline orientations of the grains present in a probe of $100\ifmmode\times\else\texttimes\fi{}100$ $\ensuremath{\mu}\mathrm{m}{}^{2}$ can be determined from the Cr $K$ edge. Interestingly, it is also revealed that a static disorder is involved in the studied thin films. These findings highlight that, given the overall agreement between experimental and calculated spectra, the ${\mathrm{Cr}}_{2}\mathrm{AlC}$ electronic structure is accurately predicted using density functional theory.