Library Item
First-Order Raman Scattering of the MAX phases Ta4AlC3, Nb4AlC3, Ti4AlN3 and Ta2AlC
Description:
Herein we report on the Raman spectra of the following ternary hexagonal carbides and nitrides (MAX phases): Ta4AlC3, Ta2AlC and Ti4AlN3. We also present the Raman-active modes of α- and β-Ta4AlC3, Nb4AlC3 and Ti4AlN3, – also referred to as the 413 MAX phases – as predicted from first principles calculations using density functional theory. We compare the experimental and calculated results obtained herein with previous studies on Ta2AlC and Ti4AlN3. The vibrational behavior associated with the Raman-active modes for the 413 phases has been identified for the first time. In general, the agreement is good between theory and experiment.
The experimental and calculated results indicate that the modes at low wavenumbers – dominated by the Al atoms – are a weak function of chemistry and the differences in energy can be traced to variations in the reduced mass. The modes at higher wavenumbers are dominated by the C and N atoms and show a strong dependency of the unit cell chemistry, with the Ta-C bond being stiffer than the Nb-C bond, which is in turn stiffer than Ti-N.
