Editing Β-Carbon nitride

{{lowercasetitle}}
{{Chembox
| ImageFile = 4 11nitride.svg
| ImageCaption = Lattice structure of (β-C<sub>3</sub>N<sub>4</sub>).
| IUPACName = β-Carbon nitride

|Section1={{Chembox Identifiers
| MeSHName = Carbon+nitride
| StdInChI_Ref = 
| StdInChI = 1S/N4C3/c1-5-2-6(1)3(5)7(1,2)4(5)6
| StdInChIKey_Ref = 
| StdInChIKey = 
| SMILES = N13[C]25N4[C]16N2[C]34N56
| InChIKey = 
 }}
|Section2={{Chembox Properties
| C=3 | N=4
 }}
| Section4 = {{Chembox Structure
| Structure_ref = <ref name="ref5">{{ cite journal |author1=Yin, L. W. |author2=Li, M. S. |author3=Liu, Y. X. |author4=Sui, J. L. |author5=Wang, J. M. | title = Synthesis of Beta Carbon Nitride Nanosized Crystal through Mechanochemical Reaction | journal = Journal of Physics: Condensed Matter | volume = 15 | issue = 2 | pages = 309–314 | year = 2003 | doi = 10.1088/0953-8984/15/2/330 |bibcode=2003JPCM...15..309Y |s2cid=250752987 }}</ref>
| CrystalStruct = [[Hexagonal]], [[Pearson symbol|hP14]]
| SpaceGroup = P6<sub>3</sub>/m No. 176
| LattConst_a = 6.36 Å
| LattConst_c = 4.648 Å 
 }}
}}
'''β-Carbon nitride''' (''beta''-carbon nitride), β-C<sub>3</sub>N<sub>4</sub>, is a [[superhard material]] predicted to be harder than diamond.<ref>{{ cite journal | journal = Nature | date = 2000 | title = News: Crunchy filling | author = Ball, P. | doi = 10.1038/news000511-1 | s2cid = 211729235 }}</ref>

The material was first proposed in 1985 by Amy Liu and [[Marvin L. Cohen]]. Examining the nature of [[crystalline]] [[covalent bond|bonds]] they theorised that [[carbon]] and [[nitrogen]] atoms could form a particularly short and strong bond in a stable [[crystal lattice]] in a ratio of 1:1.3, and that this material could be harder than [[diamond]].<ref name="ref2">{{ cite journal |author1=Liu, A. Y. |author2=Cohen, M. L. | title = Prediction of New Low Compressibility Solids  | journal = Science | volume = 245 | issue = 4920 | doi = 10.1126/science.245.4920.841 | pages = 841–842 | year = 1989 | pmid=17773359|bibcode=1989Sci...245..841L |s2cid=39596885 |url=https://zenodo.org/record/1230990 }}</ref>

Nanosized crystals and nanorods of β-carbon nitride can be prepared by mechanochemical processing.<ref>{{ cite journal |author1=Niu, C. |author2=Lu, Y. Z. |author3=Lieber, C. M. | title = Experimental Realization of the Covalent Solid Carbon Nitride | journal = Science | volume = 261 | issue = 5119 | pages = 334–337 | year = 1993 | doi = 10.1126/science.261.5119.334 | pmid=17836844|bibcode=1993Sci...261..334N |s2cid=21070125 }}</ref><ref>{{ cite journal | author1 = Martín-Gil, J. | author2 = Martín-Gil, F. J. | author3 = Sarikaya, M. | author4 = Qian, M. | author5 = José-Yacamán, M. | author6 = Rubio, A. | title = Evidence of a Low-Compressibility Carbon Nitride with Defect-Zincblende Structure | journal = Journal of Applied Physics | volume = 81 | issue = 6 | pages = 2555–2559 | year = 1997 | doi = 10.1063/1.364301 | bibcode = 1997JAP....81.2555M }}</ref><ref name="ref5"/><ref name="ref6">{{ cite journal |author1=Yin, L. W. |author2=Bando, Y. |author3=Li, M. S. |author4=Liu, Y. X. |author5=Qi, Y. X. | title = Unique Single-Crystalline Beta Carbon Nitride Nanorods | journal = Advanced Materials | volume = 15 | issue = 21 | pages = 1840–1844 | year = 2003 | doi =  10.1002/adma.200305307 |bibcode=2003AdM....15.1840Y |s2cid=95431446 }}</ref>

== Production ==

=== Processing ===
β-C<sub>3</sub>N<sub>4</sub> can be synthesized in a mechanochemical reaction. This method involves [[ball milling]] of high-purity graphite powders down to an amorphous nanoscale size under an argon atmosphere. Then argon is replaced by an NH<sub>3</sub> gas atmosphere, which helps to form nanosized flake-like β-C<sub>3</sub>N<sub>4</sub>.<ref name="ref5" /> During ball milling, fracture and welding of the reactants and graphite powder particles occur repeatedly from ball/powder collisions. [[Plastic deformation]] of the graphite powder particles occur due to the shear bands decomposing into sub-grains that are separated by low-angle grain boundaries, further milling decreases the sub-grain size until nanosize sub-grains form. The high pressure and intense motion promotes [[catalytic]] dissociation of NH<sub>3</sub> molecules into [[monatomic]] nitrogen on the fractured surface of the carbon. Nanosized carbon powders act substantially different from its bulk material as a result of particle dimension and surface area, causing the nanosized carbon to easily react with the free nitrogen atoms, forming β-C<sub>3</sub>N<sub>4</sub> powder.<ref name="ref6" />

=== Producing nanorods ===
Single crystal β-C<sub>3</sub>N<sub>4</sub> nanorods can be formed after the powder-like or flake-like compound is thermally [[annealing (metallurgy)|annealed]] with an NH<sub>3</sub> gas flow. The size of the nanorods is determined by the temperature and time of thermal annealing. These nanorods grow faster in their axis direction than the diameter direction and have hemispherical-like ends. A cross section of the nanorods indicates that their section morphology is prismatic. It was discovered that they contain amorphous phases, however when annealed to 450&nbsp;°C  for three hours under an NH<sub>3</sub> atmosphere, the amount of the amorphous phase diminished to almost none. These nanorods are dense and twinned rather than nanotubes. Synthesizing these nanorods through thermal annealing provides an effective, low-cost, high-yield method for the synthesis of single crystal nanorods.<ref name="ref6" />

=== Alternate methods of synthesis ===
Rather than forming a powder or nanorod, the carbon nitride compound can alternatively be formed in thin amorphous films by either shock-wave compression technology, [[pyrolysis]] of high nitrogen content precursors, diode sputtering, [[Solvothermal synthesis|solvothermal]] preparation, pulsed laser [[ablation]], or [[ion implantation]].<ref name="ref6" />

=== Difficulties of processing ===
Although extensive studies on the process and synthesis of the formed carbon nitride have been reported, the nitrogen concentration of the compound tends to be below the ideal composition for C<sub>3</sub>N<sub>4</sub>. This is due to the low [[thermodynamic stability]] with respect to carbon phases and N<sub>2</sub> gas, indicated by a positive value of the [[Standard enthalpy of formation|enthalpies of formation]]. The commercial exploitation of nanopowders is very limited by the high synthesis cost along with difficult methods of production that causes a low yield.<ref name="ref5" /><ref name="ref6" />

== Characteristics ==

=== Morphology===
β-C<sub>3</sub>N<sub>4</sub> has the same crystal structure as β-[[Silicon nitride|Si<sub>3</sub>N<sub>4</sub>]] with a [[hexagonal]] network of tetrahedrally (sp<sup>3</sup>) bonded carbon and trigonal planar nitrogen (sp<sup>2</sup>).<ref name="ref6" /> [[Thermal annealing]] can be used to change the crystal morphology from flake-like into sphere- or rod-like structures.<ref name="ref5" /> The nanorods are generally straight and contain no other defects.<ref name="ref6" />

=== Properties ===
A hardness equal or above that of diamond (the hardest known material) has been predicted,<ref name="ref2" /> but not yet demonstrated.

== See also ==
* [[Graphitic carbon nitride]]
* [[Heterodiamond]]
* [[Superhard materials]]

==References==
{{reflist}}

{{Nitrides}}

[[Category:Nitrides]]
[[Category:Superhard materials]]