Lattice dynamics of Al‐containing MAX‐phase carbides: a first‐principle study

A systematic study on lattice dynamics of M n  + 1 AlC n ( n  = 1–3) phases using first‐principle calculations is reported, where the Raman‐active and infrared‐active (IR) modes are emphasized. The highest phonon wavenumber is related to the vibration of C atoms. The ‘imaginary wavenumber’ in the phonon spectrum of Nb 3 AlC 2 contributes to the composition gap in Nb‐Al‐C system (Nb 2 AlC and Nb 4 AlC 3 do appear in experiments, but there are no experimental reports on Nb 3 AlC 2 ). The full set of Raman‐active and IR‐active modes in the 211, 312, and 413 M n  + 1 AX n phases is identified, with the corresponding Raman and IR wavenumbers. The 211, 312, and 413 M n  + 1 AX n phases have 4, 6, and 8 IR‐active modes, respectively. There is no distinct difference among the wavenumber ranges of IR‐active modes for 211, 312, and 413 phases, with the highest wavenumber of 780 cm −1 in Ta 4 AlC 3 . The Raman wavenumbers of M 2 AlC phases all decrease with increasing the d‐electron shell number of transition metal M. However, this case is valid only for the Raman‐active modes with low wavenumbers of M 3 AlC 2 and M 4 AlC 3 . Copyright © 2015 John Wiley & Sons, Ltd.