View source for Chemistry:Material properties of diamond

{{Short description|none}}
{{Infobox mineral
| name        = Diamond
| category    = Native Nonmetal, [[Earth:Mineral|Mineral]]
| boxwidth    =
| boxbgcolor  =
| image       = Rough diamond.jpg
| caption     = An octahedral diamond crystal in matrix
| formula     = Carbon (C)
| molweight   =
| color       = Most often colorless to yellow or brown; rarely pink, orange, green, blue, gray, or red
| habit       = Octahedral, cubo-octahedral, spherical, or cubic
| system      = [[Diamond cubic]]<br>([[Earth:Lattice constant|''a'']] = 3.56683 [[Ångström|Å]])
| twinning    =
| cleavage    = Perfect; parallel to the octahedral face
| fracture    = Irregular
| mohs        = 10
| luster      =
| refractive  = 2.417
| opticalprop =
| birefringence =
| pleochroism = None
| streak      = white
| gravity     = 3.516–3.525
| melt        =
| fusibility  = Burns above 700 °C in air.
| other = boiling point = none, very low vapor pressure before decomposing in solid state
| diagnostic  =
| solubility  = Resistant to acids, but dissolves irreversibly in hot steel
| diaphaneity = Clear to not
| var1 = [[Chemistry:Ballas|Ballas]]|var1text = Spherical, radial structure, cryptocrystalline, opaque black
| var2 = [[Chemistry:Bort|Bort]]|var2text = Poorly formed, cryptocrystalline, shapeless, translucent
| var3 = [[Chemistry:Carbonado|Carbonado]]|var3text = Massive, microcrystalline, opaque black
}}

[[Chemistry:Diamond|Diamond]] is the [[Chemistry:Allotropes of carbon|allotrope of carbon]] in which the [[Chemistry:Carbon|carbon]] atoms are arranged in the specific type of [[Cubic crystal system|cubic lattice]] called [[Diamond cubic|diamond cubic]]. It is a [[Earth:Crystal|crystal]] that is transparent to opaque and which is generally isotropic (no or very weak [[Physics:Birefringence|birefringence]]). Diamond is the [[Physics:Hardness|hardest]] naturally occurring material known. Yet, due to important structural brittleness, bulk diamond's [[Engineering:Fracture toughness|toughness]] is only fair to good. The precise [[Physics:Tensile strength|tensile strength]] of bulk diamond is little known; however, compressive strength up to {{val|60|ul=GPa}} has been observed, and it could be as high as {{val|90|-|100|u=GPa}} in the form of micro/nanometer-sized wires or needles (~{{val|100|-|300|u=nm}} in diameter, micrometers long), with a corresponding maximum tensile elastic strain in excess of 9%.<ref name="auto">{{cite journal |last1=Dang |first1=Chaoqun |display-authors=0 |title=Achieving large uniform tensile elasticity in microfabricated diamond |journal=Science |date=January 1, 2021 |volume=371 |issue=6524 |pages=76–78 |pmid=33384375 |bibcode=2021Sci...371...76D |doi=10.1126/science.abc4174 |doi-access=free}}</ref><ref>{{cite journal |last1=Banerjee |first1=Amit |display-authors=0 |title=Ultralarge elastic deformation of nanoscale diamond |journal=Science |date=20 Apr 2018 |volume=360 |issue=6386 |pages=300–302 |pmid=29674589 |bibcode=2018Sci...360..300B |doi=10.1126/science.aar4165 |doi-access=free}}</ref> The [[Anisotropy|anisotropy]] of diamond hardness is carefully considered during [[Engineering:Diamond cutting|diamond cutting]]. Diamond has a high [[Physics:Refractive index|refractive index]] (2.417) and moderate [[Physics:Dispersion (optics)|dispersion]] (0.044) properties that give cut diamonds their brilliance. Scientists classify diamonds into four main types according to the nature of crystallographic defects present. Trace impurities substitutionally replacing carbon atoms in a diamond's [[Chemistry:Crystal structure|crystal structure]], and in some cases structural defects, are responsible for the wide range of colors seen in diamond. Most diamonds are electrical insulators and extremely efficient [[Physics:Thermal conductivity|thermal conductor]]s. Unlike many other minerals, the [[Physics:Specific gravity|specific gravity]] of diamond crystals (3.52) has rather small variation from diamond to diamond.

==Hardness and crystal structure==
Known to the ancient Greeks as {{lang|grc|ἀδάμας}} ({{transliteration|grc|adámas}}, 'proper, unalterable, unbreakable')<ref>
{{cite web |last1=Liddell |first1=H.G. |last2=Scott |first2=R. |title=Adamas |work=A Greek–English Lexicon |publisher=[[Perseus Project]] |url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3D%231145&redirect=true}}</ref> and sometimes called adamant, diamond is the hardest known naturally occurring material, and serves as the definition of 10 on the [[Physics:Mohs scale of mineral hardness|Mohs scale of mineral hardness]]. Diamond is extremely strong owing to its crystal structure, known as [[Diamond cubic|diamond cubic]], in which each carbon atom has four neighbors covalently bonded to it. Bulk cubic [[Chemistry:Boron nitride|boron nitride]] (c-BN) is nearly as hard as diamond. Diamond reacts with some materials, such as steel, and c-BN wears less when cutting or abrading such material.<ref>{{cite web |last=Ing |first=Pavel Brazda Dpl |date=2006-02-01 |title=Hard Choices: Diamond or CBN? {{!}} Gear Solutions Magazine Your Resource to the Gear Industry |url=https://gearsolutions.com/features/hard-choices-diamond-or-cbn/ |access-date=2023-05-25 |language=en-US}}</ref> (Its zincblende structure is like the diamond cubic structure, but with alternating types of atoms.) A currently hypothetical material, [[Chemistry:Beta carbon nitride|beta carbon nitride]] (β-{{chem2|C3N4}}), may also be as hard or harder in one form. It has been shown that some diamond [[Physics:Aggregated diamond nanorod|aggregates]] having nanometer grain size are harder and tougher than conventional large diamond crystals, thus they perform better as abrasive material.<ref name=blank/><ref name=iri/> Owing to the use of those new ultra-hard materials for diamond testing, more accurate values are now known for diamond hardness. A surface perpendicular to the [111] [[Physics:Crystallography#Notation|crystallographic direction]] (that is the longest diagonal of a cube) of a pure (i.e., type IIa) diamond has a hardness value of {{val|167|u=GPa}} when scratched with a [[Physics:Aggregated diamond nanorod|nanodiamond]] tip, while the nanodiamond sample itself has a value of {{val|310|u=GPa}} when tested with another nanodiamond tip. Because the test only works properly with a tip made of harder material than the sample being tested, the true value for nanodiamond is likely somewhat lower than {{val|310|u=GPa}}.<ref name=blank/>

[[File:visualisation diamond cubic.svg|thumb|left|upright|Visualisation of a diamond cubic unit cell: 1. Components of a unit cell, 2. One unit cell, 3. A lattice of 3×3×3 unit cells]]
[[File:Diamond-pV.svg|thumb|245px|Molar volume vs. pressure at room temperature.]]
[[File:diamond lattice.stl|thumb|3D ball-and-stick model of a diamond lattice]]
The precise [[Physics:Tensile strength|tensile strength]] of diamond is unknown, though strength up to {{val|60|u=GPa}} has been observed, and theoretically it could be as high as {{val|90|-|225|u=GPa}} depending on the sample volume/size, the perfection of diamond lattice and on its orientation: Tensile strength is the highest for the [[Physics:Miller index|[100] crystal direction]] (normal to the cubic face), smaller for the [110] and the smallest for the [111] axis (along the longest cube diagonal).<ref name=Telling/> Diamond also has one of the smallest [[Physics:Compressibility|compressibilities]] of any material.

[[Cubic crystal system|Cubic]] diamonds have a perfect and easy [[Octahedron|octahedral]] [[Physics:Cleavage (crystal)|cleavage]], which means that they only have four [[Plane (geometry)|plane]]s—weak directions following the [[Face (geometry)|face]]s of the octahedron where there are fewer bonds—along which diamond can easily split upon blunt impact to leave a smooth surface. Similarly, diamond's hardness is markedly ''directional'': the hardest direction is the diagonal on the [[Cube|cube]] face, 100 times harder than the softest direction, which is the [[Dodecahedron|dodecahedral]] plane. The octahedral plane is intermediate between the two extremes. The [[Engineering:Diamond cutting|diamond cutting]] process relies heavily on this directional hardness, as without it a diamond would be nearly impossible to fashion. [[Physics:Cleavage (crystal)|Cleavage]] also plays a helpful role, especially in large stones where the cutter wishes to remove flawed material or to produce more than one stone from the same piece of rough (e.g. Cullinan Diamond).<ref name=read/>

Diamonds crystallize in the diamond cubic [[Crystal system|crystal system]] ([[Space group|space group]] Fd{{overline|3}}m) and consist of [[Tetrahedron|tetrahedrally]], covalently bonded carbon atoms. A second form called [[Chemistry:Lonsdaleite|lonsdaleite]], with hexagonal symmetry, has also been found, but it is extremely rare and forms only in meteorites or in laboratory synthesis. The local environment of each atom is identical in the two structures. From theoretical considerations, lonsdaleite is expected to be harder than diamond, but the size and quality of the available stones are insufficient to test this hypothesis.<ref name=PanZicheng/> In terms of [[Physics:Crystal habit|crystal habit]], diamonds occur most often as euhedral (well-formed) or rounded octahedra and [[Physics:Crystal twinning|twinned]], flattened octahedra with a triangular outline. Other forms include dodecahedra and (rarely) cubes. There is evidence that [[Chemistry:Nitrogen|nitrogen]] impurities play an important role in the formation of well-shaped euhedral crystals. The largest diamonds found, such as the Cullinan Diamond, were shapeless. These diamonds are pure (i.e. type II) and therefore contain little if any nitrogen.<ref name=read/>

The faces of diamond octahedrons are highly [[Earth:Lustre (mineralogy)|lustrous]] owing to their hardness; triangular shaped growth defects (''trigons'') or ''etch pits'' are often present on the faces. A diamond's [[Physics:Fracture|fracture]] is irregular. Diamonds which are nearly round, due to the formation of multiple steps on octahedral faces, are commonly coated in a gum-like skin (''nyf''). The combination of stepped faces, growth defects, and nyf produces a "scaly" or corrugated appearance. Many diamonds are so distorted that few crystal faces are discernible. Some diamonds found in {{wipe|Brazil}} and the Democratic Republic of the Congo are [[Earth:Cryptocrystalline|polycrystalline]] and occur as opaque, darkly colored, spherical, radial masses of tiny crystals; these are known as ballas and are important to industry as they lack the cleavage planes of single-crystal diamond. [[Chemistry:Carbonado|Carbonado]] is a similar opaque [[Earth:Microcrystalline|microcrystalline]] form which occurs in shapeless masses. Like ballas diamond, carbonado lacks cleavage planes and its specific gravity varies widely from 2.9 to 3.5. [[Chemistry:Bort|Bort]] diamonds, found in Brazil, Venezuela, and Guyana, are the most common type of industrial-grade diamond. They are also polycrystalline and often poorly crystallized; they are translucent and cleave easily.<ref name=read/>

===Hydrophobia and Lipophilia===
Due to great hardness and strong molecular bonding, a cut diamond's [[Physics:Facet|facet]]s and facet edges appear the flattest and sharpest. A curious side effect of a natural diamond's surface perfection is ''hydrophobia'' combined with ''lipophilia''. The former property means a drop of water placed on a diamond forms a coherent droplet, whereas in most other minerals the water would spread out to cover the surface. Additionally, diamond is unusually lipophilic, meaning [[Chemistry:Petroleum|grease]] and [[Chemistry:Oil|oil]] readily collect and spread on a diamond's surface, whereas in other minerals oil would form coherent drops. This property is exploited in the use of grease pencils, which apply a line of grease to the surface of a suspect [[Physics:Diamond simulant|diamond simulant]]. Diamond surfaces are [[Chemistry:Hydrophobe|hydrophobic]] when the surface carbon atoms terminate with a hydrogen atom and [[Chemistry:Hydrophile|hydrophilic]] when the surface atoms terminate with an oxygen atom or [[Chemistry:Hydroxyl radical|hydroxyl radical]]. Treatment with gases or [[Chemistry:Chalcedony|plasma]]s containing the appropriate gas, at temperatures of {{val|450|u=degC}} or higher, can change the surface property completely.<ref name="HansenJ"/> Naturally occurring diamonds have a surface with less than a half monolayer coverage of oxygen, the balance being hydrogen and the behavior is moderately hydrophobic. This allows for separation from other minerals at the mine using the so-called "grease-belt".<ref name="Harlow"/>

==Toughness==
[[File:Diamond blade very macro.jpg|thumb|Diamonds in an [[Engineering:Angle grinder|angle grinder]] blade]]
Unlike hardness, which denotes only resistance to scratching, diamond's [[Engineering:Fracture toughness|toughness]] or tenacity is only fair to good. Toughness relates to the ability to resist breakage from falls or impacts. Because of diamond's perfect and easy cleavage, it is vulnerable to breakage. A diamond will shatter if hit with an ordinary hammer.<ref>{{cite web |last=The Action Lab |title=Can You Break a Diamond With a Hammer? |website=[[Company:YouTube|YouTube]] |url=https://www.youtube.com/watch?v=XBjiEsAyNQs |access-date=14 June 2020 |url-status=live |archive-url=https://ghostarchive.org/varchive/youtube/20211116/XBjiEsAyNQs |archive-date=2021-11-16}}{{cbignore}}</ref> The toughness of natural diamond has been measured as {{val|2.0|u=MPa.m.5}}, which is good compared to other gemstones like aquamarine (blue colored), but poor compared to most engineering materials. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamond has a cleavage plane and is therefore more fragile in some orientations than others. Diamond cutters use this attribute to cleave some stones, prior to faceting.<ref name=WeberMJ/><ref name=FieldJE/>

Ballas and carbonado diamond are exceptional, as they are polycrystalline and therefore much tougher than single-crystal diamond; they are used for deep-drilling bits and other demanding industrial applications.<ref name=Moriyoshi/> Particular faceting shapes of diamonds are more prone to breakage and thus may be uninsurable by reputable insurance companies. The [[Chemistry:Diamond cut|brilliant cut]] of gemstones is designed specifically to reduce the likelihood of breakage or splintering.<ref name=read/>

Solid foreign crystals are commonly present in diamond. They are mostly minerals, such as [[Chemistry:Olivine|olivine]], [[Chemistry:Garnet|garnet]]s, [[Chemistry:Ruby|ruby]], and many others.<ref name=IakoubovskiiFe/> These and other inclusions, such as internal fractures or "feathers", can compromise the structural integrity of a diamond. Cut diamonds that have been [[Chemistry:Diamond enhancement|enhanced]] to improve their [[Chemistry:Diamond clarity|clarity]] via glass infilling of fractures or cavities are especially fragile, as the glass will not stand up to [[Physics:Ultrasonic cleaning|ultrasonic cleaning]] or the rigors of the jeweler's torch. Fracture-filled diamonds may shatter if treated improperly.<ref name=TaylorWR/>

===Pressure resistance===
Used in so-called diamond anvil experiments to create high-pressure environments, diamonds withstand crushing pressures in excess of 600 gigapascals (6 million [[Physics:Standard atmosphere (unit)|atmospheres]]).<ref name=DiamondAnvil/>

==Optical properties==

===Color and its causes===
[[File:HPHTdiamonds2.JPG|thumb|Synthetic diamonds of various colors grown by the high-pressure high-temperature technique. The diamond size is ~{{val|2|u=mm}}.]]
[[File:irrdiamond.jpg|thumb|Pure diamonds, before and after irradiation and annealing. Clockwise from left bottom: 1) initial ({{val|2|×|2|u=mm}}); 2–4) irradiated by different doses of {{val|2|u=MeV}} electrons; 5–6) irradiated by different doses and annealed at {{val|800|u=degC}}.]]
{{Main|Chemistry:Crystallographic defects in diamond}}

Diamonds occur in various colors: black, brown, yellow, gray, white, blue, orange, purple to pink, and red. Colored diamonds contain crystallographic defects, including substitutional impurities and structural defects, that cause the coloration. Theoretically, pure diamonds would be transparent and colorless. Diamonds are scientifically classed into two main ''types'' and several subtypes, according to the nature of defects present and how they affect light absorption:<ref name=read/>

Type I diamond has [[Chemistry:Nitrogen|nitrogen]] (N) atoms as the main impurity, at a concentration of up to 1%. If the N atoms are in pairs or larger aggregates, they do not affect the diamond's color; these are Type Ia. About 98% of gem diamonds are type Ia: these diamonds belong to the ''Cape series'', named after the diamond-rich region formerly known as Cape Province in {{wipe|South Africa}}, whose deposits are largely Type Ia. If the nitrogen atoms are dispersed throughout the crystal in isolated sites (not paired or grouped), they give the stone an intense yellow or occasionally brown tint (type Ib); the rare canary diamonds belong to this type, which represents only ~0.1% of known natural diamonds. Synthetic diamond containing nitrogen is usually of type Ib. Type Ia and Ib diamonds absorb in both the [[Physics:Infrared|infrared]] and [[Physics:Ultraviolet|ultraviolet]] region of the [[Physics:Electromagnetic spectrum|electromagnetic spectrum]], from {{val|320|u=nm}}. They also have a characteristic fluorescence and visible absorption spectrum.<ref name=walker/>

Type II diamonds have very few if any nitrogen impurities. Pure (type IIa) diamond can be colored pink, red, or, brown owing to structural anomalies arising through ''plastic deformation'' during crystal growth;<ref name=Hounsome/> these diamonds are rare (1.8% of gem diamonds), but constitute a large percentage of Australian diamonds. Type IIb diamonds, which account for ~0.1% of gem diamonds, are usually a steely blue or gray due to boron atoms scattered within the crystal matrix. These diamonds are also [[Physics:Semiconductor|semiconductor]]s, unlike other diamond types (see Electrical properties). Most blue-gray diamonds coming from the Argyle mine of Australia are not of type IIb, but of Ia type. Those diamonds contain large concentrations of defects and impurities (especially hydrogen and nitrogen) and the origin of their color is yet uncertain.<ref name=argyle/> Type II diamonds weakly absorb in a different region of the infrared (the absorption is due to the diamond lattice rather than impurities), and transmit in the ultraviolet below 225&nbsp;nm, unlike type I diamonds. They also have differing fluorescence characteristics, but no discernible visible absorption spectrum.<ref name=walker/>

Certain [[Chemistry:Diamond enhancement|diamond enhancement]] techniques are commonly used to artificially produce an array of colors, including blue, green, yellow, red, and black. Color enhancement techniques usually involve [[Biology:Irradiation|irradiation]], including [[Physics:Proton|proton]] bombardment via [[Physics:Cyclotron|cyclotron]]s; [[Physics:Neutron|neutron]] bombardment in the piles of [[Physics:Nuclear reactor|nuclear reactor]]s; and [[Physics:Electron|electron]] bombardment by [[Organization:Van de Graaff generator|Van de Graaff generator]]s. These high-energy particles physically alter the diamond's [[Physics:Crystal lattice|crystal lattice]], knocking carbon atoms out of place and producing color centers. The depth of color penetration depends on the technique and its duration, and in some cases the diamond may be left [[Physics:Radioactive|radioactive]] to some degree.<ref name=read/><ref name=read2/>

Some irradiated diamonds are completely natural; one famous example is the Dresden Green Diamond.<ref name=Harlow/> In these natural stones the color is imparted by "radiation burns" (natural irradiation by [[Physics:Alpha particle|alpha particle]]s originating from [[Earth:Uranium ore|uranium ore]]) in the form of small patches, usually only [[Micrometre|micrometers]] deep. Additionally, Type IIa diamonds can have their structural deformations "repaired" via a high-pressure high-temperature (HPHT) process, removing much or all of the diamond's color.<ref name=collins/>

===Luster===
[[File:Brillanten.jpg|thumb|left|A scattering of round-brilliant cut diamonds shows the many reflecting facets.]]
The [[Earth:Lustre (mineralogy)|luster]] of a diamond is described as "adamantine", which simply means diamond-like. Reflections on a properly cut diamond's facets are undistorted, due to their flatness. The [[Physics:Refractive index|refractive index]] of diamond (as measured via sodium light, {{val|589.3|u=nm}}) is 2.417. Because it is cubic in structure, diamond is also isotropic. Its high [[Physics:Dispersion (optics)|dispersion]] of 0.044 (variation of refractive index across the visible spectrum) manifests in the perceptible ''fire'' of cut diamonds. This fire—flashes of [[Physics:Prism (optics)|prismatic]] colors seen in transparent stones—is perhaps diamond's most important optical property from a jewelry perspective. The prominence or amount of fire seen in a stone is heavily influenced by the choice of [[Chemistry:Diamond cut|diamond cut]] and its associated proportions (particularly crown height), although the body color of fancy (i.e., unusual) diamonds may hide their fire to some degree.<ref name=read2/>

More than 20 other minerals have higher dispersion (that is difference in refractive index for blue and red light) than diamond, such as [[Chemistry:Titanite|titanite]] 0.051, [[Chemistry:Andradite|andradite]] 0.057, [[Chemistry:Cassiterite|cassiterite]] 0.071, [[Chemistry:Strontium titanate|strontium titanate]] 0.109, [[Chemistry:Sphalerite|sphalerite]] 0.156, synthetic [[Chemistry:Rutile|rutile]] 0.330, [[Chemistry:Cinnabar|cinnabar]] 0.4, etc. (see [[Physics:Dispersion (optics)|Dispersion (optics)]]).<ref name=Schumann/> However, the combination of dispersion with extreme hardness, wear and chemical resistivity, as well as clever marketing, determines the exceptional value of diamond as a gemstone.
{{Clear}}

===Fluorescence===
{{Multiple image
|align     = right
|direction = vertical
|header    =
|width     = 200
|image1    = diaTr1.jpg
|caption1  =
|image2    = diaPL1.jpg
|caption2  = A photograph (top) and UV-excited photoluminescence image (bottom) from a plate cut from a synthetic diamond (width ~3&nbsp;mm). Most of yellow color and green emission originate from [[Chemistry:Nickel|nickel]] impurities.}}

Diamonds exhibit [[Biology:Fluorescence|fluorescence]], that is, they emit light of various colors and intensities under long-wave ultraviolet light (365&nbsp;nm): Cape series stones (type Ia) usually fluoresce blue, and these stones may also [[Physics:Phosphorescence|phosphoresce]] yellow, a unique property among gemstones. Other possible long-wave fluorescence colors are green (usually in brown stones), yellow, mauve, or red (in type IIb diamonds).<ref name=phosph/> In natural diamonds, there is typically little if any response to short-wave ultraviolet, but the reverse is true of synthetic diamonds. Some natural type IIb diamonds phosphoresce blue after exposure to short-wave ultraviolet. In natural diamonds, fluorescence under [[Physics:X-ray|X-ray]]s is generally bluish-white, yellowish or greenish. Some diamonds, particularly Canadian diamonds, show no fluorescence.<ref name=walker/><ref name=read2/>

The origin of the luminescence colors is often unclear and not unique. Blue emission from type IIa and IIb diamonds is reliably identified with dislocations by directly correlating the emission with dislocations in an [[Engineering:Electron microscope|electron microscope]].<ref name=Hanley/> However, blue emission in type Ia diamond could be either due to dislocations or the N3 defects (three nitrogen atoms bordering a vacancy).<ref name=vanWyk/> Green emission in natural diamond is usually due to the H3 center (two substitutional nitrogen atoms separated by a vacancy),<ref name=H3/> whereas in synthetic diamond it usually originates from [[Chemistry:Nickel|nickel]] used as a catalyst (see figure).<ref name=walker/> Orange or red emission could be due to various reasons, one being the [[Physics:Nitrogen-vacancy center|nitrogen-vacancy center]] which is present in sufficient quantities in all types of diamond, even type IIb.<ref name=Freitas/>

===Optical absorption===
Cape series (Ia) diamonds have a visible [[Physics:Absorption spectrum|absorption spectrum]] (as seen through a direct-vision spectroscope) consisting of a fine line in the violet at {{val|415.5|u=nm}}; however, this line is often invisible until the diamond has been cooled to very low temperatures. Associated with this are weaker lines at {{val|478|u=nm}}, {{val|465|u=nm}}, {{val|452|u=nm}}, {{val|435|u=nm}}, and {{val|423|u=nm}}.
All those lines are labeled as N3 and N2 optical centers and associated with a defect consisting of three nitrogen atoms bordering a vacancy. Other stones show additional bands: brown, green, or yellow diamonds show a band in the green at {{val|504|u=nm}} (H3 center, see above),<ref name=H3/> sometimes accompanied by two additional weak bands at {{val|537|u=nm}} and {{val|495|u=nm}} (H4 center, a large complex presumably involving 4 substitutional nitrogen atoms and 2 lattice vacancies).<ref name=deSaES/> Type IIb diamonds may absorb in the far red due to the substitutional boron, but otherwise show no observable visible absorption spectrum.<ref name=read/>

[[Earth:Gemology|Gemological]] laboratories make use of [[Physics:Spectrophotometer|spectrophotometer]] machines that can distinguish natural, artificial, and color-[[Chemistry:Diamond enhancement|enhanced diamonds]]. The spectrophotometers analyze the [[Physics:Infrared|infrared]], visible, and [[Physics:Ultraviolet|ultraviolet]] absorption and luminescence spectra of diamonds cooled with [[Chemistry:Liquid nitrogen|liquid nitrogen]] to detect tell-tale absorption lines that are not normally discernible.<ref name=read/><ref name=identification/>

==Electrical properties==
Diamond is a good electrical insulator, having a resistivity of {{val|100|u=GΩ.m}} to {{val|1|u=EΩ.m}}<ref name=Fromentin/> ({{val|1.0e11}} – {{val|1.0e18|ul=Ω.m}}), and is famous for its wide [[Physics:Band gap|bandgap]] of 5.47 eV. High carrier mobilities<ref>{{cite journal |last1=Isberg |first1=Jan |last2=Hammersberg |first2=Johan |last3=Johansson |first3=Erik |last4=Wikström |first4=Tobias |last5=Twitchen |first5=Daniel J. |last6=Whitehead |first6=Andrew J. |last7=Coe |first7=Steven E. |last8=Scarsbrook |first8=Geoffrey A. |date=2002-09-06 |title=High Carrier Mobility in Single-Crystal Plasma-Deposited Diamond |journal=Science |language=en |volume=297 |issue=5587 |pages=1670–1672 |pmid=12215638 |bibcode=2002Sci...297.1670I |s2cid=27736134 |issn=0036-8075 |doi=10.1126/science.1074374 |url=https://www.science.org/doi/10.1126/science.1074374}}</ref> and high electric breakdown field<ref>{{cite journal |last1=Volpe |first1=Pierre-Nicolas |last2=Muret |first2=Pierre |last3=Pernot |first3=Julien |last4=Omnès |first4=Franck |last5=Teraji |first5=Tokuyuki |last6=Jomard |first6=François |last7=Planson |first7=D. |last8=Brosselard |first8=Pierre |last9=Dheilly |first9=Nicolas |last10=Vergne |first10=Bertrand |last11=Scharnholtz |first11=Sigo |date=September 2010 |title=High breakdown voltage Schottky diodes synthesized on p-type CVD diamond layer |journal=Physica Status Solidi A |language=en |volume=207 |issue=9 |pages=2088–2092 |bibcode=2010PSSAR.207.2088V |s2cid=122210971 |doi=10.1002/pssa.201000055 |url=https://onlinelibrary.wiley.com/doi/10.1002/pssa.201000055}}</ref> at room temperature are also important characteristics of diamond. Those characteristics allow single crystalline diamond to be one of the promising materials for [[Physics:Semiconductor|semiconductor]]s. Its wide [[Physics:Band gap|bandgap]] helps semiconductors to keep their quality because it secures high resistivity even in high temperature (high power supply). Semiconductors whose carrier mobilities are high such as diamond do not need high input voltage, which make it easier to utilize in the industry. High breakdown voltage avoids semiconductors from huge current suddenly occurs at a certain input voltage.

Most natural blue diamonds are an exception and are semiconductors due to substitutional [[Chemistry:Boron|boron]] impurities replacing carbon atoms. Natural blue or blue-gray diamonds, common for the Argyle diamond mine in Australia, are rich in [[Chemistry:Hydrogen|hydrogen]]; these diamonds are not semiconductors and it is unclear whether hydrogen is actually responsible for their blue-gray color.<ref name="argyle"/> Natural blue diamonds containing boron and synthetic diamonds [[Chemistry:Dopant|doped]] with boron are p-type semiconductors. N-type diamond films are reproducibly synthesized by phosphorus doping during chemical vapor deposition.<ref name="Koizumi2008"/> Diode [[Physics:P-n junction|p-n junction]]s and UV light emitting diodes ([[Engineering:LED|LED]]s, at {{val|235|u=nm}}) have been produced by sequential deposition of p-type (boron-doped) and n-type (phosphorus-doped) layers.<ref name="koizumi2001"/>
Diamond's electronic properties can be also modulated by [[Physics:Strain engineering|strain engineering]].<ref name="auto"/>

Diamond [[Engineering:Transistor|transistor]]s have been produced (for research purposes).<ref name=DT>{{cite journal |title=Diamond transistor performance and fabrication |journal=Proceedings of the IEEE |volume=79 |issue=5 |pages=669–676 |year=1991 |last1=Geis |first1=M.W. |bibcode=1991IEEEP..79..669G |doi=10.1109/5.90131}}</ref> FETs with SiN dielectric layers, and SC-FETs have been made.<ref>{{cite journal |title=Diamond Based Field-Effect Transistors of Zr Gate with SiN<sub>x</sub> Dielectric Layers |journal=Journal of Nanomaterials |volume=2015 |pages=1–5 |year=2015 |last1=Wang |first1=W. |last2=Hu |first2=C. |last3=Li |first3=S. Y. |last4=Li |first4=F. N. |last5=Liu |first5=Z. C. |last6=Wang |first6=F. |last7=Fu |first7=J. |last8=Wang |first8=H. X. |doi=10.1155/2015/124640 |doi-access=free |url=https://www.researchgate.net/publication/283282236}}</ref>

In April 2004, the journal Nature reported that below the superconducting transition temperature {{val|4|ul=K}}, boron-doped diamond synthesized at high temperature and high pressure is a bulk superconductor.<ref name=Ekimov/> Superconductivity was later observed in heavily boron-doped films grown by various chemical vapor deposition techniques, and the highest reported transition temperature (by 2009) is {{val|11.4|u=K}}.<ref name=Takano2007/><ref name=Takano2006/> (See also [[Physics:Covalent superconductor#Diamond|Covalent superconductor]])

Uncommon magnetic properties (spin glass state) were observed in diamond nanocrystals intercalated with potassium.<ref name=Kozlov/> Unlike paramagnetic host material, magnetic susceptibility measurements of intercalated nanodiamond revealed distinct ferromagnetic behavior at {{val|5|u=K}}. This is essentially different from results of potassium intercalation in graphite or C60 fullerene, and shows that sp3 bonding promotes magnetic ordering in carbon. The measurements presented first experimental evidence of intercalation-induced spin-glass state in a nanocrystalline diamond system.

==Thermal conductivity==
Unlike most electrical insulators, diamond is a good conductor of heat because of the strong covalent bonding and low [[Physics:Phonon scattering|phonon scattering]]. Thermal conductivity of natural diamond was measured to be about 2,200&nbsp;W/(m·K), which is five times more than [[Chemistry:Silver|silver]], the most thermally conductive metal. Monocrystalline synthetic diamond [[Physics:Isotopically pure diamond|enriched to 99.9% the isotope <sup>12</sup>C]] had the highest [[Physics:Thermal conductivity|thermal conductivity]] of any known solid at room temperature: 3,320&nbsp;W/(m·K), though reports exist of superior thermal conductivity in both carbon nanotubes and graphene.<ref name=Anthony1990/><ref name=PNU/> Because diamond has such high thermal conductance it is already used in semiconductor manufacture to prevent [[Chemistry:Silicon|silicon]] and other semiconducting materials from overheating. At lower temperatures conductivity becomes even better, and reaches 41,000&nbsp;W/(m·K) at {{convert|104|K|C F|abbr=on}} (<sup>12</sup>C-enriched diamond).<ref name=PNU/>

Diamond's high thermal conductivity is used by jewelers and gemologists who may employ an electronic ''thermal probe'' to distinguish diamonds from their imitations. These probes consist of a pair of battery-powered [[Engineering:Thermistor|thermistor]]s mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. This test takes about 2–3 seconds. However, older probes will be fooled by [[Chemistry:Moissanite|moissanite]], a crystalline mineral form of [[Chemistry:Silicon carbide|silicon carbide]] introduced in 1998 as an alternative to diamonds, which has a similar thermal conductivity.<ref name=read/><ref name=identification/>

Technologically, the high thermal conductivity of diamond is used for the efficient heat removal in high-end power electronics. Diamond is especially appealing in situations where electrical conductivity of the heat sinking material cannot be tolerated e.g. for the thermal management of high-power radio-frequency ({{abbr|RF|radio frequency}}) [[Physics:Microcoil|microcoil]]s that are used to produce strong and local RF fields.<ref>{{cite journal |title=Broadband radio-frequency transmitter for fast nuclear spin control |journal=Review of Scientific Instruments |volume=91 |issue=11 |pages=113106 |year=2020 |last1=Herb |first1=Konstantin |last2=Zopes |first2=Jonathan |last3=Cujia |first3=Kristian |last4=Degen |first4=Christian |pmid=33261455 |arxiv=2005.06837 |bibcode=2020RScI...91k3106H |s2cid=227252470 |doi=10.1063/5.0013776}}</ref>

==Thermal stability==
[[File:Diamond and graphite2.jpg|thumb|Diamond and graphite are two allotropes of carbon: pure forms of the same element that differ in structure.]]
If heated over {{cvt|700|C|F|abbr=on}} in air, diamond, being a form of carbon, oxidizes and its surface blackens, but the surface can be restored by re-polishing.<ref name="JohnP"/> In absence of oxygen, e.g. in a flow of high-purity [[Chemistry:Argon|argon]] gas, diamond can be heated up to about {{val|1700|u=degC}}.<ref name=Davies1972/><ref name=Evans1964/> At high pressure (~{{cvt|20|GPa|psi|abbr=on}}) diamond can be heated up to {{cvt|2500|C|F|abbr=on}},<ref name=Evans1981/> and a report published in 2009 suggests that diamond can withstand temperatures of {{cvt|3000|C|F|abbr=on}} and above.<ref name=Shatskiy/>

Diamonds are carbon [[Earth:Crystal|crystal]]s that form under high temperatures and extreme pressures such as deep within the Earth. At surface air pressure (one atmosphere), diamonds are not as stable as [[Chemistry:Graphite|graphite]], and so the decay of diamond is [[Physics:Thermodynamics|thermodynamically]] favorable (δ''H''&nbsp;=&nbsp;{{val|−2|u=kJ/mol}}).<ref name=read2/> However, owing to a very large [[Physics:Kinetic energy|kinetic energy]] barrier, diamonds are metastable; they will not decay into graphite under [[Standard temperature and pressure|normal conditions]].<ref name=read2/>

==See also==
{{Div col|colwidth=30em}}
*Chemical vapor deposition of diamond
*[[Chemistry:Crystallographic defects in diamond|Crystallographic defects in diamond]]
*[[Physics:Nitrogen-vacancy center|Nitrogen-vacancy center]]
*[[Earth:Synthetic diamond|Synthetic diamond]]
{{Div col end}}

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}}

==Further reading==
*Pagel-Theisen, Verena. (2001). ''Diamond grading ABC: The manual'' (9th ed.), pp.&nbsp;84–85. Rubin & Son n.v.; Antwerp, Belgium. {{ISBN|3-9800434-6-0}}
*Webster, Robert, and Jobbins, E. Allan (Ed.). (1998). ''Gemmologist's compendium'', p.&nbsp;21, 25, 31. St Edmundsbury Press Ltd, Bury St Edwards. {{ISBN|0-7198-0291-1}}

==External links==
*[http://www.ioffe.ru/SVA/NSM/Semicond/Diamond/index.html Properties of diamond]
*[https://www.stevesque.com/diamond/ Properties of diamond] (S. Sque, PhD thesis, 2005, University of Exeter, UK)

{{DEFAULTSORT:Diamond (material properties)}}
[[Category:Diamond|Material properties of diamond]]
[[Category:Allotropes of carbon]]
[[Category:Native element minerals]]
[[Category:Superhard materials]]

{{Sourceattribution|Material properties of diamond}}