Ytterbium is achemical element; it hassymbolYb andatomic number 70. It is a metal, the fourteenth element in thelanthanide series, which is the basis of the relative stability of its +2oxidation state. Like the other lanthanides, its most common oxidation state is +3, as in itsoxide,halides, and other compounds. Inaqueous solution, like compounds of other late lanthanides, soluble ytterbium compounds form complexes with nine water molecules. Because of its closed-shell electron configuration, its density, melting point and boiling point are much lower than those of most other lanthanides.
In 1878, Swiss chemistJean Charles Galissard de Marignac separated from the rare earth "erbia", another independent component, which he called "ytterbia", forYtterby, the village in Sweden near where he found the new component oferbium. He suspected that ytterbia was a compound of a new element that he called "ytterbium". Four elements were named after the village, the others beingyttrium,terbium, anderbium. In 1907, the new earth "lutecia" was separated from ytterbia, from which the element "lutecium", nowlutetium, was extracted byGeorges Urbain,Carl Auer von Welsbach, andCharles James. After some discussion, Marignac's name "ytterbium" was retained. A relatively pure sample of the metal was first obtained in 1953. At present, ytterbium is mainly used as adopant of stainless steel oractive laser media, and less often as agamma ray source.
Natural ytterbium is a mixture of seven stable isotopes, which altogether are present at an average concentration of 0.3parts per million in the Earth's crust. This element is mined in China, the United States, Brazil, and India in form of the mineralsmonazite,euxenite, andxenotime. The ytterbium concentration is low because it is found only among many otherrare-earth elements. It is among the least abundant. Once extracted and prepared, ytterbium is somewhat hazardous as an eye and skin irritant. The metal is a fire and explosion hazard.
Ytterbium has threeallotropes labeled by the Greek letters alpha, beta and gamma. Their transformation temperatures are −13 °C and 795 °C,[10] although the exact transformation temperature depends on thepressure andstress.[11] The beta allotrope (6.966 g/cm3) exists at room temperature, and it has aface-centered cubiccrystal structure. The high-temperature gamma allotrope (6.57 g/cm3) has abody-centered cubic crystalline structure.[10] The alpha allotrope (6.903 g/cm3) has ahexagonal crystalline structure and is stable at low temperatures.[12]
The beta allotrope has a metallicelectrical conductivity at normal atmospheric pressure, but it becomes asemiconductor when exposed to a pressure of about 16,000atmospheres (1.6 GPa). Its electricalresistivity increases ten times upon compression to 39,000 atmospheres (3.9 GPa), but then drops to about 10% of its room-temperature resistivity at about 40,000 atm (4.0 GPa).[10][13]
Contrary to most other lanthanides, which have a close-packed hexagonal lattice, ytterbium crystallizes in the face-centered cubic system. Ytterbium has a density of 6.973 g/cm3, which is significantly lower than those of the neighboring lanthanides,thulium (9.32 g/cm3) andlutetium (9.841 g/cm3). Its melting and boiling points are also significantly lower than those of thulium and lutetium. This is due to the closed-shell electron configuration of ytterbium ([Xe] 4f14 6s2), which causes only the two 6s electrons to be available formetallic bonding (in contrast to the other lanthanides where three electrons are available) and increases ytterbium'smetallic radius.[12]
Ytterbium metal tarnishes slowly in air, taking on a golden or brown hue. Finely dispersed ytterbium readily oxidizes in air and under oxygen. Mixtures of powdered ytterbium withpolytetrafluoroethylene orhexachloroethane burn with an emerald-green flame.[15] Ytterbium reacts withhydrogen to form variousnon-stoichiometrichydrides. Ytterbium dissolves slowly in water, but quickly in acids, liberating hydrogen.[12]
Ytterbium is quiteelectropositive, and it reacts slowly with cold water and quite quickly with hot water to form ytterbium(III) hydroxide:[16]
The ytterbium(III) ion absorbs light in thenear-infrared range of wavelengths, but not invisible light, soytterbia, Yb2O3, is white in color and the salts of ytterbium are also colorless. Ytterbium dissolves readily in dilutesulfuric acid to form solutions that contain the colorless Yb(III) ions, which exist as nonahydrate complexes:[16]
Although usually trivalent, ytterbium readily forms divalent compounds. This behavior is unusual forlanthanides, which almost exclusively form compounds with an oxidation state of +3. The +2 state has a valenceelectron configuration of 4f14 because the fully filledf-shell gives more stability. The yellow-green ytterbium(II) ion is a very strongreducing agent and decomposes water, releasinghydrogen, and thus only the colorless ytterbium(III) ion occurs inaqueous solution.Samarium andthulium also behave this way in the +2 state, buteuropium(II) is stable in aqueous solution. Ytterbium metal behaves similarly to europium metal and the alkaline earth metals, dissolving in ammonia to form blueelectride salts.[12]
Natural ytterbium is composed of seven stableisotopes:168Yb,170Yb,171Yb,172Yb,173Yb,174Yb, and176Yb, with174Yb being the most abundant (31.90%natural abundance). Thirty-two syntheticradioisotopes have been observed, with the most stable being169Yb with ahalf-life of 32.014 days,175Yb with a half-life of 4.185 days, and166Yb with a half-life of 56.7 hours. All of the remainingradioactive isotopes have half-lives that are less than 2 hours, with the majority of them being less than 20 minutes. This element also has 18meta states, with the most stable being169mYb (half-life 46 seconds).[9]
The known isotopes of ytterbium range from149Yb to187Yb.[9][17] The primarydecay mode for those isotopes lighter than the most abundant stable isotope,174Yb, iselectron capture givingthulium isotopes; the primary mode after isbeta emission givinglutetium isotopes.
Ytterbium is found with otherrare-earth elements in several rareminerals. It is most often recovered commercially frommonazite sand (0.03% ytterbium). The element is also found ineuxenite andxenotime. The main mining areas are China, the United States,Brazil, India,Sri Lanka, and Australia. Reserves of ytterbium are estimated as one milliontonnes. Ytterbium is normally difficult to separate from other rare earths, bution-exchange andsolvent extraction techniques developed in the mid- to late 20th century have simplified separation.Compounds of ytterbium are rare and have not yet been well characterized. The abundance of ytterbium in the Earth's crust is about 3 mg/kg.[13]
As an even-numbered lanthanide, in accordance with theOddo–Harkins rule, ytterbium is significantly more abundant than its immediate neighbors,thulium andlutetium, which occur in the same concentrate at levels of about 0.5% each. The world production of ytterbium is only about 50 tonnes per year, reflecting that it has few commercial applications.[13] Microscopic traces of ytterbium are used as adopant in theYb:YAG laser, asolid-state laser in which ytterbium is the element that undergoesstimulated emission ofelectromagnetic radiation.[18]
Ytterbium is often the most common substitute inyttrium minerals. In very few known cases/occurrences ytterbium prevails over yttrium, as, e.g., inxenotime-(Yb). A report of native ytterbium from the Moon'sregolith is known.[19]
It is relatively difficult to separate ytterbium from other lanthanides due to its similar properties. As a result, the process is somewhat long. First, minerals such asmonazite orxenotime are dissolved into various acids, such assulfuric acid. Ytterbium can then be separated from other lanthanides byion exchange, as can other lanthanides. The solution is then applied to aresin, to which different lanthanides bind with different affinities. This is then dissolved usingcomplexing agents, and due to the different types of bonding exhibited by the different lanthanides, it is possible to isolate the compounds.[20][21]
Ytterbium is separated from other rare earths either byion exchange or by reduction with sodium amalgam. In the latter method, a buffered acidic solution of trivalent rare earths is treated with molten sodium-mercury alloy, which reduces and dissolves Yb3+. The alloy is treated withhydrochloric acid. The metal is extracted from the solution as oxalate and converted to oxide by heating. The oxide is reduced to metal by heating withlanthanum,aluminium,cerium orzirconium in high vacuum. The metal is purified by sublimation and collected over a condensed plate.[22]
The chemical behavior of ytterbium is similar to that of the rest of thelanthanides. Most ytterbium compounds are found in the +3 oxidation state, and its salts in this oxidation state are nearly colorless. Likeeuropium,samarium, andthulium, the trihalides of ytterbium can be reduced to the dihalides byhydrogen,zinc dust, or by the addition of metallic ytterbium.[12] The +2 oxidation state occurs only in solid compounds and reacts in some ways similarly to thealkaline earth metal compounds; for example, ytterbium(II) oxide (YbO) shows the same structure ascalcium oxide (CaO).[12]
Ytterbium forms both dihalides and trihalides with thehalogensfluorine,chlorine,bromine, andiodine. The dihalides are susceptible to oxidation to the trihalides at room temperature and disproportionate to the trihalides and metallic ytterbium at high temperature:[12]
Ytterbium reacts with oxygen to formytterbium(III) oxide (Yb2O3), which crystallizes in the "rare-earth C-type sesquioxide" structure which is related to thefluorite structure with one quarter of the anions removed, leading to ytterbium atoms in two different six coordinate (non-octahedral) environments.[27] Ytterbium(III) oxide can be reduced toytterbium(II) oxide (YbO) with elemental ytterbium, which crystallizes in the same structure assodium chloride.[12]
Ytterbium dodecaboride (YbB12) is a crystalline material that has been studied to understand various electronic and structural properties of many chemically related substances. It is aKondo insulator.[28] It is aquantum material; under normal conditions, the interior of the bulk crystal is aninsulator whereas the surface is highlyconductive.[29] Among therare earth elements, ytterbium is one of the few that can form a stable dodecaboride, a property attributed to its comparatively small atomic radius.[30]
In 1878, Ytterbiumwas discovered by the Swiss chemistJean Charles Galissard de Marignac. While examining samples ofgadolinite, Marignac found a new component in the earth then known aserbia, and he named it ytterbia, forYtterby, the Swedish village near where he found the new component of erbium. Marignac suspected that ytterbia was a compound of a new element that he called "ytterbium".[13][26][31][32][33]
In 1907, the French chemistGeorges Urbain separated Marignac's ytterbia into two components:neoytterbia andlutecia. Neoytterbia later became known as the element ytterbium, and lutecia became known as the elementlutetium. The Austrian chemistCarl Auer von Welsbach independently isolated these elements from ytterbia at about the same time, but he called themaldebaranium (Ad; afterAldebaran) andcassiopeium.[13] The American chemistCharles James also independently isolated these elements at about the same time.[34]
Urbain and Welsbach accused each other of publishing results based on the other party.[35][36][37] In 1909, the Commission on Atomic Mass, consisting ofFrank Wigglesworth Clarke,Wilhelm Ostwald, and Georges Urbain, which was then responsible for the attribution of new element names, settled the dispute by granting priority to Urbain and adopting his names as official ones, based on the fact that the separation of lutetium from Marignac's ytterbium was first described by Urbain.[35] After Urbain's names were recognized,neoytterbium was reverted toytterbium.
The chemical and physical properties of ytterbium could not be determined with any precision until 1953, when the first nearly pure ytterbium metal was produced by usingion-exchange processes.[13] The price of ytterbium was relatively stable between 1953 and 1998 at about US$1,000/kg.[38]
The169Ybisotope (with ahalf-life of 32 days), which is created along with the short-lived175Yb isotope (half-life 4.2 days) byneutron activation during theirradiation of ytterbium innuclear reactors, has been used as aradiation source in portableX-ray machines. Like X-rays, thegamma rays emitted by the source pass through soft tissues of the body, but are blocked by bones and other dense materials. Thus, small169Yb samples (which emit gamma rays) act like tiny X-ray machines useful forradiography of small objects. Experiments show that radiographs taken with a169Yb source are roughly equivalent to those taken with X-rays having energies between 250 and 350 keV.169Yb is also used innuclear medicine.[39]
In 2013, a pair of experimental atomic clocks based on ytterbium atoms at theNational Institute of Standards and Technology (NIST) set a record for stability. NIST physicists reported the ytterbium clocks' ticks are stable to within less than two parts in 1quintillion (1 followed by 18 zeros), roughly 10 times better than the previous best published results for other atomic clocks. The clocks would be accurate within a second for a period comparable to the age of the universe. These clocks rely on about 10,000 ytterbium atomslaser-cooled to 10 microkelvin (10 millionths of a degree aboveabsolute zero) and trapped in anoptical lattice—a series of pancake-shaped wells made of laser light. Another laser that "ticks" 518 trillion times per second (518 THz) provokes a transition between two energy levels in the atoms. The large number of atoms is key to the clocks' high stability.[40]
Visible light waves oscillate faster than microwaves, hence optical clocks can be more precise thancaesiumatomic clocks. ThePhysikalisch-Technische Bundesanstalt is working on several such optical clocks. The model with one single ytterbium ion caught in anion trap is highly accurate. The optical clock based on it is exact to 17 digits after the decimal point.[41]
Ytterbium can also be used as adopant to help improve the grain refinement, strength, and other mechanical properties ofstainless steel. Some ytterbiumalloys have rarely been used indentistry.[10][13]
The Yb3+ion is used as adoping material inactive laser media, specifically insolid state lasers anddouble clad fiber lasers. Ytterbium lasers are highly efficient, have long lifetimes and can generate short pulses; ytterbium can also easily be incorporated into the material used to make the laser.[42] Ytterbium lasers commonly radiate in the 1.03–1.12 μm band beingoptically pumped at wavelength 900 nm–1 μm, dependently on the host and application. The smallquantum defect makes ytterbium a prospective dopant for efficient lasers andpower scaling.[43]
The kinetic of excitations in ytterbium-doped materials is simple and can be described within the concept ofeffective cross-sections; for most ytterbium-doped laser materials (as for many other optically pumped gain media), theMcCumber relation holds,[44][45][46] although the application to the ytterbium-dopedcomposite materials was under discussion.[47][48]
Usually, low concentrations of ytterbium are used. At high concentrations, the ytterbium-doped materials showphotodarkening[49](glass fibers) or even a switch to broadband emission[50] (crystals and ceramics) instead of efficient laser action. This effect may be related with not only overheating, but also with conditions ofcharge compensation at high concentrations of ytterbium ions.[51]
Much progress has been made in the power scaling lasers and amplifiers produced with ytterbium (Yb) doped optical fibers. Power levels have increased from the 1 kW regimes due to the advancements in components as well as the Yb-doped fibers. Fabrication of Low NA, Large Mode Area fibers enable achievement of near perfect beam qualities (M2<1.1) at power levels of 1.5 kW to greater than 2 kW at ~1064 nm in a broadband configuration.[52] Ytterbium-doped LMA fibers also have the advantages of a larger mode field diameter, which negates the impacts of nonlinear effects such as stimulatedBrillouin scattering and stimulatedRaman scattering, which limit the achievement of higher power levels, and provide a distinct advantage over single mode ytterbium-doped fibers.
To achieve even higher power levels in ytterbium-based fiber systems, all factors of the fiber must be considered. These can be achieved only through optimization of all ytterbium fiber parameters, ranging from the core background losses to the geometrical properties, to reduce the splice losses within the cavity. Power scaling also requires optimization of matching passive fibers within the optical cavity.[53] The optimization of the ytterbium-doped glass itself through host glass modification of various dopants also plays a large part in reducing the background loss of the glass, improvements in slope efficiency of the fiber, and improved photodarkening performance, all of which contribute to increased power levels in 1 μm systems.
Ytterbium metal increases its electrical resistivity when subjected to high stresses. This property is used in stress gauges to monitor ground deformations from earthquakes and explosions.[58]
Although ytterbium is fairly stable chemically, it is stored in airtight containers and in an inert atmosphere such as a nitrogen-filled dry box to protect it from air and moisture.[60] All compounds of ytterbium are treated as highlytoxic, although studies appear to indicate that the danger is minimal. However, ytterbium compounds cause irritation to human skin and eyes, and some might beteratogenic.[61] Metallic ytterbium dust can spontaneously combust.[62]
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