Theoretical screening, intrinsic brittleness and thermal properties of the S-containing MAX carbides and borides

Lattice dynamics, Raman and IR vibrations of stable Al/Si‐containing MAB phases: An ab initio and experimental study

“…This would result in a greater atomic displacement, which is the possible reason why MoAlB can be easily etched with a layer of Al to obtain Mo 2 AlB 2 in an acidic environment, while Mo 2 AlB 2 cannot be etched to be MBenes. 52 Similarly, the vibration frequency of all MAX phases is usually lower than 20 THz, 17,48 but the MAB phases commonly selected for etching, such as MoAlB and Cr 2 AlB 2 , have a higher one, making the preparation experiment of MBenes unable to prepare two-dimensional derivatives. 46,60 To understand the effect of mass and chemical bonding on the phonon frequency, it starts from a typical harmonic oscillator with the vibrational frequency 𝜔 = √ 𝑘∕𝑚,…”

“…The ternary layered transition-metal carbides, nitrides and borides, [1][2][3] including the MAX phases 4,5 and MAB phases, [6][7][8] have garnered significant attention because of their potential high-temperature structural [9][10][11] and functional applications. [12][13][14][15] Due to their distinctive layered structure [16][17][18] and diverse elemental compositions, 5,19,20 these phases combine the desirable properties of ceramics, such as high hardness, 21 high moduli, and resistance to oxidation and radiation, 22 with the noteworthy characteristics of metals, such as high electrical and thermal conductivity, 23 excellent thermal shock resistance, 24 ease of processing, high fracture toughness, and remark-able damage tolerance. 21 Moreover, the discovery of their two-dimensional derivatives, namely MXenes [25][26][27] and MBenes, 7,28,29 has unveiled new possibilities in terms of applications like electromagnetic shielding, 30 seawater desalination, 31 and enhancement of Raman signals.…”

“…48,49 Moreover, the phonon vibration frequencies at the gamma point, which correspond to the zero wave vector, are of great significance as they can exhibit Raman or infrared (IR) activities. 17 Beyond their role in identifying and characterizing a compound through Raman and infrared techniques using the calculated database obtained here, these activities facilitate the reflection of changes in the bond length, bond strength, atomic transfer, and vacancies by the blue shift and red one relative to the standard peak position, alongside the vibration modes: For instance, the observed blue shift in vibration peaks under external load can be utilized to calculate load information, making it a valuable tool as a mechanical sensor. 50 Similarly, changes in peak intensity resulting from radiation can indicate the degree of lattice disorder and the presence of inverse defects, aiding in the study of the radiation tolerance mechanisms of MAB phases.…”