ytterbium [for Ytterby, a town in Sweden], metallic chemical element; symbol Yb; at. no. 70; at. wt. 173.04; m.p. 819°C;; b.p. about 1,194°C;; sp. gr. about 7.0; valence +2 or +3. Ytterbium is a soft, malleable, ductile, lustrous silver-white metal. Although it is one of the rare-earth metals of the lanthanide series in Group 3 of the periodic table, in some of its chemical and physical properties it more closely resembles calcium, strontium, and barium. It exhibits allotropy; at room temperature a face-centered cubic crystalline form is stable. The metal tarnishes slowly in air and reacts slowly with water but rapidly dissolves in mineral acids. It forms numerous compounds, some of which are yellow or green. The oxide (ytterbia, Yb₂O₃) is colorless. It is widely distributed in a number of minerals, e.g., gadolinite, and is recovered from monazite but has no commercial uses. Its discovery is credited to J. C. G. de Marignac, who in 1878 separated a substance he called ytterbia. In 1907, Georges Urbain showed that this substance contained lutetium in addition to ytterbium. At about this same time C. A. von Welsbach independently discovered ytterbium and called it aldebaranium.

Ytterbium is a chemical element with the symbol Yb and atomic number 70. A soft silvery metallic element, ytterbium is a rare earth of the lanthanide series and is found in the minerals gadolinite, monazite, and xenotime. The element is sometimes associated with yttrium or other related elements and is used in certain steels. Natural ytterbium is a mix of seven stable isotopes.

Characteristics

Ytterbium is a soft, malleable and rather ductile element that exhibits a bright silvery luster. A rare earth element, it is easily attacked and dissolved by mineral acids, slowly reacts with water, and oxidizes in air.

Ytterbium has three allotropes which are called alpha, beta and gamma and whose transformation points are at −13 °C and 795 °C. The beta form exists at room temperature and has a face-centered crystal structure while the high-temperature gamma form has a body-centered crystal structure.

Normally, the beta form has a metallic-like electrical conductivity, but becomes a semiconductor when exposed to around 16,000 atm (1.6 GPa). Its electrical resistivity is tenfold larger at about 39,000 atm (3.9 GPa) but then drops dramatically, to around 10% of its room temperature resistivity value, at 40,000 atm (4 GPa).

Ytterbium is one of the lanthanides that is able to become divalent. Like the other potentially divalent lanthanides, samarium and europium, it is capable of being extracted into mercury by the use of sodium amalgam, which made it one of the easier lanthanides to purify using classical techniques. However, this divalency was not discovered until the 20th century.

Ytterbium(III) ion absorbs light in the near infra-red, but not in the visible region, so that ytterbia is white, and ytterbium salts of colorless anions are also colorless.

History

Ytterbium was discovered by the Swiss chemist Jean Charles Galissard de Marignac in 1878. Marignac found a new component in the earth then known as erbia and named it ytterbia (after Ytterby, the Swedish town where he found the new erbia component). He suspected that ytterbia was a compound of a new element he called ytterbium.

In 1907, the French chemist Georges Urbain separated Marignac's ytterbia into two components, neoytterbia and lutecia. Neoytterbia would later become known as the element ytterbium and lutecia would later be known as the element lutetium. Auer von Welsbach independently isolated these elements from ytterbia at about the same time but called them aldebaranium and cassiopeium.

The chemical and physical properties of ytterbium could not be determined until 1953 when the first nearly pure ytterbium was produced.

Ytterbium oxide first became commercially available in significant quantities the mid to late 1950's, as a result of the development of ion-exchange separation technology using EDTA as eluting agent, and copper(II) as the retaining ion, which was invented at Iowa State University's Ames Laboratory by Frank Spedding and co-workers. In a price list dated January 20, 1959, the Lindsay Chemical Division of American Potash and Chemical Corporation, which at the time was the largest producer of rare earths in the world, was offering 99% ytterbium oxide at 160 dollars per pound, and their 99.9% grade at 200 dollars per pound. The minimum order quantity was 5 grams, priced at 70 or 90 cents per gram, respectively. In modern times, kilogram quantities of ytterbium oxide have been available from specialists in rare earths priced between 100 and 200 dollars per kilogram.

Occurrence

Ytterbium is found with other rare earth elements in several rare minerals. It is most often recovered commercially from monazite sand (0.03% ytterbium). The element is also found in euxenite and xenotime. Ytterbium is normally difficult to separate from other rare earths, but ion-exchange and solvent extraction techniques developed in the mid to late 20th century have simplified separation. Known compounds of ytterbium are rare—they haven't been well characterized yet.

The most important current (2008) sources of ytterbium are the ionic adsorption clays of southern China. The "High Yttrium" concentrate derived from some versions of these comprise about two thirds yttria by weight, and 3-4% ytterbia. As an even-numbered lanthanide, in accordance with the Oddo-Harkins rule, ytterbium is significantly more abundant than its immediate neighbors, thulium and lutetium, which occur in the same concentrate at levels of about 0.5% each.

Isotopes

Naturally occurring ytterbium is composed of 7 stable isotopes, Yb-168, Yb-170, Yb-171, Yb-172, Yb-173, Yb-174, and Yb-176, with Yb-174 being the most abundant (31.83% natural abundance). 27 radioisotopes have been characterized, with the most stable being Yb-169 with a half-life of 32.026 days, Yb-175 with a half-life of 4.185 days, and Yb-166 with a half life of 56.7 hours. All of the remaining radioactive isotopes have half-lifes that are less than 2 hours, and the majority of these have half lifes that are less than 20 minutes. This element also has 12 meta states, with the most stable being Yb-169m (t_½ 46 seconds).

The isotopes of ytterbium range in atomic weight from 147.9674 u (Yb-148) to 180.9562 u (Yb-181). The primary decay mode before the most abundant stable isotope, Yb-174 is electron capture, and the primary mode after is beta emission. The primary decay products before Yb-174 are element 69 (thulium) isotopes, and the primary products after are element 71 (lutetium) isotopes. Of interest to modern quantum optics, the different ytterbium isotopes follow either Bose-Einstein statistics or Fermi-Dirac statistics, leading to interesting behavior in optical lattices.

Precautions

Although ytterbium is fairly stable, it nevertheless should be stored in closed containers to protect it from air and moisture. All compounds of ytterbium should be treated as highly toxic although initial studies appear to indicate that the danger is limited. Ytterbium compounds are, however, known to cause skin and eye irritation and may be teratogenic. Metallic ytterbium dust poses a fire and explosion hazard.

Compounds

• Halides: YbCl₂, YbBr₃, YbCl₃, YbF₃
• Oxides: Yb₂O₃

Applications

Usually, a very small amount of Yb is used; either a small sample of radioactive isotope as a source of X-rays, or a small concentration dopant.

Source of X-rays

The ¹⁶⁹Yb isotope has been used as a radiation source substitute for a portable X-ray machine when electricity was not available. Like X-rays, gamma rays pass through soft tissues of the body, but are blocked by bones and other dense materials. Thus, small ¹⁶⁹Yb samples (which emit gamma rays) act like tiny X-ray machines useful for radiography of small objects.

Doping of stainless steel

Ytterbium could also be used to help improve the grain refinement, strength, and other mechanical properties of stainless steel. Some ytterbium alloys have been used in dentistry.

Yb as dopant of active media

Yb is used as dopant in optics materials, usually in the form of ions in active laser media. Several powerful double-clad fiber lasers and disk lasers use Yb³⁺ ions as dopant at concentration of several atomic percent. Glasses (optical fibers), crystals and ceramics with Yb³⁺ are used.

Ytterbium is often used as a doping material (as Yb³⁺) for high power and wavelength-tunable solid state lasers. Yb lasers commonly radiate in the 1.06–1.12µm band being optically pumped at wavelength 900nm–1µm, dependently on the host and application. Small quantum defect makes Yb prospective dopant for efficient lasers and power scaling.

The kinetic of excitations in Yb-doped materials is simple and can be described within concept of effective cross-sections; for the most of Yb-doped laser materials (as for many other optically-pumped gain media), the McCumber relation holds , although the application to the Yb-doped composite materials was under discussion .

Usually, low concentrations of Yb are used. At high concentration of excitations, the Yb-doped materials show photodarkening (glass fibers) or ever switch to the broadband emission (crystals and ceramics) instead of the efficient laser action. This effect may be related with not only overheating, but also conditions of the charge compensation at high concentration of Yb ions.

Solar cells

Ytterbium has a single absorption band at 985 nanometers, which is used to convert infrared energy into electricity in solar cells.

See also

• Erbium
• Terbium
• Yttrium

References

Also:

• Los Alamos National Laboratory – Ytterbium
• Guide to the Elements – Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1
• It's Elemental – Ytterbium

External links

• WebElements.com – Ytterbium (also used as a reference)