Raman active phonon modes and heat capacities of Ti2AlC and Cr2AlC ceramics: first-principles and experimental investigations

Abstract

Raman active phonon frequencies and corresponding vibrational eigenmodes are reported for two M2AlC ceramics, Ti2AlC and Cr2AlC, by means of first-principles calculations. The theoretical modes are approved by the experimental Raman spectrum for Ti2AlC. Compared with that of the Ti3SiC2 counterpart, the number of Raman active modes is definitely determined by the chemical formula of transition-metal carbide layers; for example, TiC0.67 in Ti3SiC2 and TiC0.5 in M2AlC. All active modes originate from stretching and bending of Al–M–C covalent bond chains, whereas the vibration of M–C bond localized inside the M6C octahedra is not Raman active. The differences in vibration characteristics between Ti2AlC and Cr2AlC are discussed in terms of atomic force constants. By including the phonon and electron contributions, trends in heat capacities as a function of temperature were illustrated and compared.

Oxidation of Cr2AlC Between 900 and 1200 °C in Air

“…They suggested the formation of protective a-Al 2 O 3 and a-Cr 2 O 3 films to be responsible. The mechanical, electrical, thermal, [1] crystal structure, [2] chemistry, [3] and physical [4] properties of Cr 2 AlC have been reported. However, there is very little information about the oxidation properties of Cr 2 AlC in the literature with the exception of Lin et al's very brief oxidation-kinetics study [2].…”

Hot corrosion and protection of Ti2AlC against Na2SO4 salt in air

“…E-mail address: yczhou@imr.ac.cn (Y. Zhou). behavior, 8 theoretical predictions, 9 thin film deposition, 10 lattice dynamics, 11,12 and microstructural characterization. 13 Poor oxidation resistance of TiAl and Ti 3 Al intermetallics at elevated temperatures has been the bottleneck to their industrial applications.…”

“…Layered-ternary Ti 2 AlC ceramic has attracted increasing interest in recent years due to its unique combination of the merits of both metals and ceramics, [1][2][3][4][5][6][7][8][9][10][11][12][13] such as, easy machinability, low density, good electrical and thermal conductivity, excellent thermal-shock and high-temperature-oxidation resistance. These salient properties make Ti 2 AlC a highly promising candidate for high-temperature structural applications or as a coating material.…”

First-principles study of the structural and elastic properties of Cr2AlX (X=N, C) compounds

“…Atomic-resolution microstructures and chemical bonding characteristics of Cr 2 AlC were characterized by high-resolution transmission electron microscopy, Z-contrast scanning transmission electron microscopy and electron energy loss spectroscopy [5]. Theoretically, Wang et al investigated the elastic stiffness, electronic band structure, Raman active phonon frequencies and corresponding vibrational eigenmodes by means of first-principles calculations [6][7][8]. Sun et al have performed theoretical studies of the structural parameters and bulk modulus of Cr 2 AlC by ab initio total energy calculations using the projector augmented wave (PAW) methods [9][10][11][12].…”