Spectroscopic ellipsometry study on the dielectric function of bulk Ti2AlN, Ti2AlC, Nb2AlC, (Ti0.5, Nb0.5)2AlC, and Ti3GeC2 MAX-phases

The averaged complex dielectric function epsilon = (2 epsilon(perpendicular to) + epsilon(parallel to))/3 of polycrystalline Ti2AlN, Ti2AlC, Nb2AlC, (Ti-0.5, Nb-0.5)(2)AlC, and Ti3GeC2 was determined by spectroscopic ellipsometry covering the mid infrared to the ultraviolet spectral range. The dielectric functions epsilon(perpendicular to) and epsilon(parallel to) correspond to the perpendicular and parallel dielectric tensor components relative to the crystallographic c-axis of these hexagonal compounds. The optical response is represented by a dispersion model with Drude-Lorentz and critical point contributions. In the low energy range the electrical resistivity is obtained from the Drude term and ranges from 0.48 mu Omega m for Ti3GeC2 to 1.59 mu Omega m for (Ti-0.5, Nb-0.5)(2)AlC. Furthermore, several compositional dependent interband electronic transitions can be identified. For the most important ones, Im(epsilon) shows maxima at: 0.78, 1.23, 2.04, 2.48, and 3.78 eV for Ti2AlN; 0.38, 1.8, 2.6, and 3.64 eV for Ti2AlC; 0.3, 0.92, and 2.8 eV in Nb2AlC; 0.45, 0.98, and 2.58 eV in (Ti-0.5, Nb-0.5)(2)AlC; and 0.8, 1.85, 2.25, and 3.02 eV in Ti3GeC2. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3525648]