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MXenes

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  • Comment: Problems: *1) Conflict of Interest almost certainly. The author should identify themselves. The writing should be more sober.*2) Overhyped, there are NO applications and predications of future breakthroughs based on DFT are too flimsy to be mentioned. DFT in general has little place here. Misplaced Pages is not a technical journal*3) the content might aim to rely on the one secondary source and minimize other sources. There is only one review in English.*4) The topic is worthwhile if it can be trimmed back. The area of research was launched in 2012, consists of about 40 publications, and is dominated by the Drexel group.*I took a stab at compressing this thing. Sorry about messing up the refs. It would not bother me to revert my work.------Smokefoot (talk) 01:17, 19 November 2014 (UTC)

In materials science, an MXene is a class of low-dimensional inorganic compounds. These materials consist of two-dimensional arrays of transition metal carbide or carbonitride. First described in 2011, MXenes combine the metallic conductivity of transition metal carbides and hydrophilic nature because of their hydroxyl or oxygen terminated surfaces.


Preparation

MXenes are produced by selectively etching out the A element from a MAX phase, which has the general formula Mn+1AXn, where M is an early transition metal, A is an element from group IIIA or IVA of the periodic table, X is C and/or N, and n = 1, 2, or 3. MAX phases have a layered hexagonal structure with P63/mmc symmetry, where M layers are nearly closed packed and X atoms fill octahedral sites. Therefore, Mn+1Xn layers are interleaved with the A element, which is metallically bonded to the M element. MAX phases are etched mainly by using strong etchants such as hydrofluoric acid (HF). Etching of Ti3AlC2 in aqueous HF at room temperature causes the A (Al) atoms to be removed, and the surface of the carbide layers to be terminated by O, OH, and/or F atoms. It has been shown how the higher the value of n in the formula, the more stable the MXene.The following MXenes have been synthesized: Ti3C2, Ti2C, V2C, Nb2C, (Ti0.5,Nb0.5)2C, Ta4C3, (V0.5,Cr0.5)3C2, Ti3CN. Although theoretically possible, nitride-based MXenes have not yet been reported.Cite error: A <ref> tag is missing the closing </ref> (see the help page).

Properties

With a high electron density near the Fermi level, MXene monolayers are predicted to be metallic. In MAX phases, N(EF) is mostly M 3d orbitals, and the valence states below EF are composed of two sub-bands. One, sub-band A, made of hybridized Ti 3d-Al 3p orbitals, is near EF, and another, sub-band B, -10 to -3 eV below EF which is due to hybridized Ti 3d-C 2p and Ti 3d-Al 3s orbitals. Said differently, sub-band A is the source of Ti-Al bonds, while sub-band B is the source of Ti-C bond. Removing A layers causes the Ti 3d states to be redistributed from missing Ti-Al bonds to delocalized Ti-Ti metallic bond states near the Fermi energy in Ti2, therefore N(EF) is 2.5-4.5 times higher for MXenes than MAX phases.

Only bare-surface MXenes are magnetic . Cr2C, Cr2N, and Ta3C2 are ferromagnetic, Ti3C2 and Ti3N2 are antiferromagnetic.

References

  1. ^ M. Naguib, V.N. Mochalin, M.W. Barsoum, Y. Gogotsi, 25th Anniversary Article: MXenes: A New Family of Two-Dimensional Materials, Advanced Materials, Volume 26, Issue 7, page 992-1005, 2014.
  2. Z. Sun, D. Music, R. Ahuja, S. Li, J. M. Schneider, Phys. Rev. B 2004, 70, 092102.

  3. Cite error: The named reference NaguibNano was invoked but never defined (see the help page).
  4. Cite error: The named reference Adv2011 was invoked but never defined (see the help page).
  5. ^ I. R. Shein, A. L. Ivanovskii, Comput. Mater. Sci. 2012, 65, 104.
  6. Cite error: The named reference Comput was invoked but never defined (see the help page).
  7. M. Khazaei, M. Arai, T. Sasaki, C.-Y. Chung, N. S. Venkataramanan, 
M. Estili, Y. Sakka, Y. Kawazoe, Adv. Funct. Mater. 2012, 23, 2185.
  8. Y. Xie, P. R. C. Kent, Phys. Rev. B 2013, 87, 235441.
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