15.3 Mxenes: Structure and Properties
15.3.1 Structure
MXenes were discovered in 2011. These are transition metal nitrides and carbides [18].
MXenes are related to the process of extracting layers of Mn+1Xn (n = 2, 3, 4) from the metal-
ceramic Mn+1AXn phase by removing interlayer A atoms (MAX, where M = generally
denotes an early transition metals Sc, Ti, Mo, Cr, Zr, Hf, Ta, V, and Nb); A indicates element
like Ga, Ti, Pb, S, Ge, Si, P, As, Cd, Sn, In, and Al, X = C, N. Mn+1 XnTx 2D layers named
MXenes are formed when the “A” layer is selectively removed by etching. The letters T
stand for -O, -OH, and –F. Furthermore, the layered structure possesses hexagonal as well
as anisotropic features along with p63/mmc space group [19].
The structure and composition of the MXenes are represented in Figure 15.1. In the
MAX phase, the arrangement of atoms has been observed in a hexagonal lattice that
includes M and X atoms, where metal atoms are shared by the edges and X atoms located
in the center. The Mn+1Xn layer can still preserve the hexagonal lattice rather than the
cubic structure of MX when the A atom is removed; hence, the Mn+1Xn layer can be
created by extracting the A atoms. M2X, M3X2, M4X3, and M5X4 are the models depicted
(Figure 15.1). MXenes thin films are often oriented horizontally, as was the case with its
predecessor MAX. The majority of MXenes have excellent mechanical qualities, and they
are predicted to be employed in nano-devices that require mechanical properties.
15.3.2 Properties
The largest range of Young’s modulus, increased electric conductivities, adjustable band
width, and higher thermal conductivities are acknowledged as characteristic features of
MXene. MXenes are distinguished from other 2D materials, such as graphene, by their
hydrophilic nature combined with improved thermal conductivities. Finally, (i) composi
tion (different transition metals “M” and “X” elements), (ii) surface and morphology
FIGURE 15.1
MXenes: Types and composition.
MXenes-Based Polymer Composites
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