Editing Boron nitride (section)

== Properties ==

===Physical===
{| class="wikitable" style="margin:0;"
|+ Properties of amorphous and crystalline BN, graphite and diamond.<br /><small>Some properties of h-BN and graphite differ within the basal planes (∥) and perpendicular to them (⟂)</small>
! rowspan=2 | Material
! colspan=4 | Boron nitride (BN)
! rowspan=2 | Graphite<ref>{{cite book | author = Delhaes, P. | title = Graphite and Precursors | publisher = CRC Press | year = 2001 | isbn = 978-9056992286}}</ref>
! rowspan=2 | Diamond<ref name=ioffe>{{cite web | url = http://www.ioffe.ru/SVA/NSM/Semicond/BN/index.html | title = BN – Boron Nitride | work = Ioffe Institute Database}}</ref>
|-
! a-<ref>{{cite journal | doi = 10.1016/0022-3093(95)00748-2 | title = Properties of Amorphous Boron Nitride Thin Films | year = 1996 | author = Zedlitz, R. | journal = Journal of Non-Crystalline Solids | volume = 198–200 | issue = Part 1 | page = 403 |bibcode = 1996JNCS..198..403Z}}</ref><ref>{{cite journal | doi = 10.1364/AO.32.000091 | pmid = 20802666 | title = Thermal Conductivities of Thin, Sputtered Optical Films | year = 1993 | author = Henager, C. H. Jr. | journal = Applied Optics | volume = 32 | issue = 1 | pages = 91–101 |bibcode = 1993ApOpt..32...91H | url = https://digital.library.unt.edu/ark:/67531/metadc1108231/}}</ref><ref>{{cite journal | doi = 10.1016/S0925-9635(98)00394-X | title = Microstructure and Mechanical Properties of Pulsed Laser Deposited Boron Nitride Films | year = 1999 | author = Weissmantel, S. | journal = Diamond and Related Materials | volume = 8 | page = 377 | issue = 2–5 |bibcode = 1999DRM.....8..377W}}</ref>
! h-
! c-<ref name=BN>{{cite book | title = Landolt-Börnstein – Group VIII Advanced Materials and Technologies: Powder Metallurgy Data. Refractory, Hard and Intermetallic Materials | chapter = 13.5 Properties of diamond and cubic boron nitride | volume = 2A2 | doi = 10.1007/b83029 | isbn = 978-3-540-42961-6 | pages = 118–139 | editor = P. Beiss | author = Leichtfried, G. | year = 2002 | publisher = Springer | location = Berlin |display-authors=etal|display-editors=etal| series = Landolt-Börnstein - Group VIII Advanced Materials and Technologies}}</ref><ref name=ioffe/>
! w-
|-
! Density (g/cm<sup>3</sup>)
| 2.28
| ~2.1
| 3.45
| 3.49
| ~2.1
| 3.515
|-
! [[Knoop hardness test|Knoop hardness]] (GPa)
| 10
|
| 45
| 34
|
| 100
|-
! [[Bulk modulus]] (GPa)
| 100
| 36.5
| 400
| 400
| 34
| 440
|-
! [[Thermal conductivity]] <br/>(W/m·K)
| 3
| 600 ∥, <br/>30 ⟂
| 740
|
| 200–2000 ∥, <br/>2–800 ⟂
| 600–2000
|-
! [[Thermal expansion]] (10<sup>−6</sup>/K)
|
| −2.7 ∥, 38 ⟂
| 1.2
| 2.7
| −1.5 ∥, 25 ⟂
| 0.8
|-
! [[Band gap]] (eV)
| 5.05
| 5.9–6.4 <ref>{{cite journal |author=Su, C. | title = Tuning colour centres at a twisted hexagonal boron nitride interface | journal = Nature Materials | volume = 21 | year = 2022 | issue = 8 | pages = 896–902 | doi = 10.1038/s41563-022-01303-4| pmid = 35835818 | bibcode = 2022NatMa..21..896S | osti = 1906698 | s2cid = 250535073 | url = https://escholarship.org/uc/item/98b013nr}}</ref>
| 10.1-10.7 <ref>{{cite journal |author1= Tararan, Anna |author2=di Sabatino, Stefano |author3=Gatti, Matteo |author4=Taniguchi, Takashi |author5=Watanabe, Kenji |author6=Reining, Lucia |author7=Tizei, Luiz H. G. |author8=Kociak, Mathieu |author9=Zobelli, Alberto| title = Optical gap and optically active intragap defects in cubic BN | journal = Phys. Rev. B | volume = 98| year = 2018| issue = 9 | pages = 094106 | doi =10.1103/PhysRevB.98.094106 | arxiv = 1806.11446 | bibcode = 2018PhRvB..98i4106T | s2cid = 119097213 | url = https://journals.aps.org/prb/abstract/10.1103/PhysRevB.98.094106}}</ref>
| 4.5–5.5
| 0
| 5.5
|-
! [[Refractive index]]
| 1.7
| 1.8
| 2.1
| 2.05
|
| 2.4
|-
! [[Magnetic susceptibility]] <br/>(µemu/g)<ref>{{cite journal |author1=Crane, T. P. |author2=Cowan, B. P. | title = Magnetic Relaxation Properties of Helium-3 Adsorbed on Hexagonal Boron Nitride | journal = Physical Review B | volume = 62 | page = 11359 | year = 2000 | doi = 10.1103/PhysRevB.62.11359 | issue = 17 |bibcode = 2000PhRvB..6211359C}}</ref> 
|
| −0.48 ∥, <br/>−17.3 ⟂
|
|
| −0.2 – −2.7 ∥, <br/>−20 – −28 ⟂
| −1.6
|}
{{clear}}
The partly [[ionic bond|ionic]] structure of BN layers in h-BN reduces covalency and electrical conductivity, whereas the interlayer interaction increases resulting in higher hardness of h-BN relative to graphite. The reduced electron-delocalization in hexagonal-BN is also indicated by its absence of color and a large [[band gap]]. Very different bonding – strong covalent within the [[basal plane]]s (planes where boron and nitrogen atoms are covalently bonded) and weak between them – causes high [[anisotropy]] of most properties of h-BN.

For example, the hardness, electrical and thermal conductivity are much higher within the planes than perpendicular to them. On the contrary, the properties of c-BN and w-BN are more homogeneous and isotropic.

Those materials are extremely hard, with the hardness of bulk c-BN being slightly smaller and w-BN even higher than that of diamond.<ref>{{cite journal | author = Pan, Z. | title = Harder than Diamond: Superior Indentation Strength of Wurtzite BN and Lonsdaleite | journal = Physical Review Letters | volume = 102 | page = 055503 | year = 2009 | doi = 10.1103/PhysRevLett.102.055503 | pmid = 19257519 | bibcode = 2009PhRvL.102e5503P | issue = 5 |display-authors=etal}}</ref> Polycrystalline c-BN with grain sizes on the order of 10&nbsp;nm is also reported to have [[Vickers hardness]] comparable or higher than diamond.<ref>{{cite journal|author=Tian, Yongjun |doi=10.1038/nature11728|title=Ultrahard nanotwinned cubic boron nitride|year=2013|journal=Nature|volume=493|issue=7432|pages=385–8|pmid=23325219|display-authors=etal|bibcode = 2013Natur.493..385T |s2cid=4419843}}</ref> Because of much better stability to heat and transition metals, c-BN surpasses diamond in mechanical applications, such as machining steel.<ref name=dkg>{{cite journal | title = Hexagonal Boron Nitride (hBN) – Applications from Metallurgy to Cosmetics | url = http://www.esk.com/uploads/tx_userjspresseveroeff/PR_0712_CFI_12-2007_Hexagonales-BN_e_01.pdf | author = Engler, M. | journal = Cfi/Ber. DKG | volume = 84 | year = 2007 | page = D25 | issn = 0173-9913}}</ref> The thermal conductivity of BN is among the highest of all electric insulators (see table).

Boron nitride can be doped p-type with beryllium and n-type with boron, sulfur, silicon or if co-doped with carbon and nitrogen.<ref name=BN/> Both hexagonal and cubic BN are wide-gap semiconductors with a band-gap energy corresponding to the UV region. If voltage is applied to h-BN<ref>{{cite journal | author = Kubota, Y. | title = Deep Ultraviolet Light-Emitting Hexagonal Boron Nitride Synthesized at Atmospheric Pressure | doi = 10.1126/science.1144216 | journal = Science | pmid = 17702939 | volume = 317 | issue = 5840 | year = 2007 | pages = 932–4 |bibcode = 2007Sci...317..932K |display-authors=etal| doi-access = free}}</ref><ref name="taniguchi">{{cite journal |author1=Watanabe, K. |author2=Taniguchi, T. |author3=Kanda, H. | title = Direct-Bandgap Properties and Evidence for Ultraviolet Lasing of Hexagonal Boron Nitride Single Crystal | doi = 10.1038/nmat1134 | journal = Nature Materials | pmid = 15156198 | volume = 3 | issue = 6 | year = 2004 | pages = 404–9 |bibcode = 2004NatMa...3..404W |s2cid=23563849}}</ref> or c-BN,<ref>{{cite journal | author = Taniguchi, T. | title = Ultraviolet Light Emission from Self-Organized p–n Domains in Cubic Boron Nitride Bulk Single Crystals Grown Under High Pressure | doi = 10.1063/1.1524295 | journal = Applied Physics Letters | volume = 81 | year = 2002 | page = 4145 | issue = 22 |bibcode = 2002ApPhL..81.4145T |display-authors=etal}}</ref> then it emits UV light in the range 215–250&nbsp;nm and therefore can potentially be used as [[light-emitting diode]]s (LEDs) or lasers.

Little is known on melting behavior of boron nitride. It degrades at 2973&nbsp;°C, but melts at elevated pressure.<ref>{{cite journal | doi = 10.1021/j100814a515 | title = Sublimation and Decomposition Studies on Boron Nitride and Aluminum Nitride | year = 1962 | author = Dreger, Lloyd H. | journal = The Journal of Physical Chemistry | volume = 66 | page = 1556 | issue = 8 |display-authors=etal}}</ref><ref name=wentorf1957>{{cite journal | doi = 10.1063/1.1745964 | title = Cubic Form of Boron Nitride | year = 1957 | author= Wentorf, R. H. | journal = The Journal of Chemical Physics | volume = 26 | issue = 4 | page = 956 | bibcode=1957JChPh..26..956W}}</ref>

===Thermal stability===
Hexagonal and cubic BN (and probably w-BN) show remarkable chemical and thermal stabilities. For example, h-BN is stable to decomposition at temperatures up to 1000&nbsp;°C in air, 1400&nbsp;°C in vacuum, and 2800&nbsp;°C in an inert atmosphere. The reactivity of h-BN and c-BN is relatively similar, and the data for c-BN are summarized in the table below. 
{| class="wikitable" style="margin:10px;"
|+ Reactivity of c-BN with solids<ref name=BN/>
! Solid
! Ambient
! Action
! Threshold temperature (°C)
|-
| Mo 
| {{val|e=-2|u=Pa}} vacuum
| Reaction 
| 1360
|-
| Ni 
| {{val|e=-2|u=Pa}} vacuum
| [[Wetting]]{{efn|Here wetting refers to the ability of a molten metal to keep contact with solid BN}}
| 1360
|-
| Fe, Ni, Co 
| Argon 
| React
| 1400–1500
|-
| Al 
| {{val|e=-2|u=Pa}} vacuum 
| Wetting and reaction 
| 1050
|-
| Si
| {{val|e=-3|u=Pa}} vacuum
| Wetting 
| 1500
|-
| Cu, Ag, Au, Ga, In, Ge, Sn 
| {{val|e=-3|u=Pa}} vacuum
| No wetting
| 1100
|-
| B 
|
| No wetting
| 2200
|-
| {{chem2|Al2O3 + B2O3}}
| {{val|e=-2|u=Pa}} vacuum
| No reaction 
| 1360
|}
{{clear}}

Thermal stability of c-BN can be summarized as follows:<ref name=BN/>
* In air or oxygen: {{chem2|B2O3}} protective layer prevents further oxidation to ~1300&nbsp;°C; no conversion to hexagonal form at 1400&nbsp;°C.
* In nitrogen: some conversion to h-BN at 1525&nbsp;°C after 12&nbsp;h.
* In vacuum ({{val|e=-5|u=Pa}}): conversion to h-BN at 1550–1600&nbsp;°C.

===Chemical stability===
Boron nitride is not attacked by the usual acids, but it is soluble in alkaline molten salts and nitrides, such as [[Lithium hydroxide|LiOH]], [[Potassium hydroxide|KOH]], [[Sodium hydroxide|NaOH]]-[[Sodium carbonate|{{chem2|Na2CO3}}]], [[Sodium nitrate|{{chem2|NaNO3}}]], [[Lithium nitride|{{chem2|Li3N}}]], [[Magnesium nitride|{{chem2|Mg3N2}}]], [[Strontium nitride|{{chem2|Sr3N2}}]], [[Barium nitride|{{chem2|Ba3N2}}]] or [[Lithium boron nitride|{{chem2|Li3BN2}}]], which are therefore used to etch BN.<ref name=BN/>

===Thermal conductivity===
The theoretical thermal conductivity of hexagonal boron nitride nanoribbons (BNNRs) can approach 1700–2000&nbsp;[[watt|W]]/([[metre|m]]⋅[[kelvin|K]]), which has the same order of magnitude as the experimental measured value for [[graphene]], and can be comparable to the theoretical calculations for graphene nanoribbons.<ref>{{cite journal | author = Lan, J. H. | title = Thermal Transport in Hexagonal Boron Nitride Nanoribbons | doi = 10.1103/PhysRevB.79.115401 | journal = Physical Review B | volume = 79 | issue = 11 | year = 2009 | page = 115401 |bibcode = 2009PhRvB..79k5401L |display-authors=etal}}</ref><ref>{{cite journal | vauthors = Hu J, Ruan X, Chen YP| title = Thermal Conductivity and Thermal Rectification in Graphene Nanoribbons: A Molecular Dynamics Study | doi = 10.1021/nl901231s| journal = Nano Letters | volume = 9 | issue = 7 | year = 2009 | pages = 2730–5 | pmid = 19499898 |arxiv = 1008.1300 |bibcode = 2009NanoL...9.2730H | s2cid = 1157650}}</ref> Moreover, the thermal transport in the BNNRs is [[anisotropic]]. The thermal conductivity of zigzag-edged BNNRs is about 20% larger than that of armchair-edged nanoribbons at room temperature.<ref>{{cite journal | title = Thermal Transport in Hexagonal Boron Nitride Nanoribbons | doi = 10.1088/0957-4484/21/24/245701 | pmid = 20484794 | journal = Nanotechnology | volume = 21 | issue = 24 | year = 2010 | page = 245701 |bibcode = 2010Nanot..21x5701O | last1 = Ouyang | first1 = Tao | last2 = Chen | first2 = Yuanping | last3 = Xie | first3 = Yuee | last4 = Yang | first4 = Kaike | last5 = Bao | first5 = Zhigang | last6 = Zhong | first6 = Jianxin | s2cid = 12898097}}</ref>

=== Mechanical properties ===
BN nanosheets consist of hexagonal boron nitride (h-BN). They are stable up to 800&nbsp;°C in air. The structure of monolayer BN is similar to that of [[graphene]], which has exceptional strength,<ref name=":0">{{Cite journal |last1=Falin |first1=Aleksey |last2=Cai |first2=Qiran |last3=Santos |first3=Elton J. G. |last4=Scullion |first4=Declan |last5=Qian |first5=Dong |last6=Zhang |first6=Rui |last7=Yang |first7=Zhi |last8=Huang |first8=Shaoming |last9=Watanabe |first9=Kenji |last10=Taniguchi |first10=Takashi |last11=Barnett |first11=Matthew R. |last12=Chen |first12=Ying |last13=Ruoff |first13=Rodney S. |last14=Li |first14=Lu Hua |date=2017-06-22 |title=Mechanical properties of atomically thin boron nitride and the role of interlayer interactions |journal=Nature Communications |language=en |volume=8 |issue=1 |pages=15815 |doi=10.1038/ncomms15815 |pmid=28639613 |pmc=5489686 |issn=2041-1723|arxiv=2008.01657 |bibcode=2017NatCo...815815F }}</ref> a high-temperature lubricant, and a substrate in electronic devices.<ref>{{Cite journal |last1=Bosak |first1=Alexey |last2=Serrano |first2=Jorge |last3=Krisch |first3=Michael |last4=Watanabe |first4=Kenji |last5=Taniguchi |first5=Takashi |last6=Kanda |first6=Hisao |date=2006-01-19 |title=Elasticity of hexagonal boron nitride: Inelastic x-ray scattering measurements |url=https://link.aps.org/doi/10.1103/PhysRevB.73.041402 |journal=Physical Review B |language=en |volume=73 |issue=4 |page=041402 |doi=10.1103/PhysRevB.73.041402 |bibcode=2006PhRvB..73d1402B |issn=1098-0121}}</ref>

The anisotropy of Young's modulus and [[Poisson's ratio]] depends on the system size.<ref>{{Cite journal |last1=Thomas |first1=Siby |last2=Ajith |first2=K M |last3=Valsakumar |first3=M C |date=2016-07-27 |title=Directional anisotropy, finite size effect and elastic properties of hexagonal boron nitride |url=https://iopscience.iop.org/article/10.1088/0953-8984/28/29/295302 |journal=Journal of Physics: Condensed Matter |volume=28 |issue=29 |pages=295302 |doi=10.1088/0953-8984/28/29/295302 |pmid=27255345 |bibcode=2016JPCM...28C5302T |issn=0953-8984}}</ref> h-BN also exhibits strongly anisotropic strength and [[toughness]],<ref>{{Cite journal |last1=Ahmed |first1=Tousif |last2=Procak |first2=Allison |last3=Hao |first3=Tengyuan |last4=Hossain |first4=Zubaer M. |date=2019-04-17 |title=Strong anisotropy in strength and toughness in defective hexagonal boron nitride |url=https://link.aps.org/doi/10.1103/PhysRevB.99.134105 |journal=Physical Review B |language=en |volume=99 |issue=13 |page=134105 |doi=10.1103/PhysRevB.99.134105 |bibcode=2019PhRvB..99m4105A |issn=2469-9950}}</ref> and maintains these over a range of [[vacancy defect]]s, showing that the anisotropy is independent to the defect type.