Orientation dependence of electron energy loss spectra and dielectric functions of Ti3SiC2 and Ti3AlC2

We employ monochromatized electron energy loss spectroscopy to study Ti3SiC2 and Ti3AlC2. By probing individual grains aligned along different axes in bulk polycrystalline Ti3SiC2 and Ti3AlC2, this approach enables determination of the anisotropy of the dielectric functions and an estimate of the free-electron lifetime in different orientations. The dielectric functions are characterized by strong interband transitions in the low energy region. The energies plasmon resonance were determined to be ≈5eV and exhibit a strong orientation-dependence. Our measurements show that the free-electron lifetimes are also highly orientation-dependent. These results suggest that scattering of carriers in MAX phases is very sensitive to composition and orientation.