ytterbium

thulium ← ytterbium → lutetium - ↑ Yb ↓ No 70Yb Periodic table
Appearance
silvery white
General properties
Name, symbol, number	ytterbium, Yb, 70
Pronunciation	/ɨˈtɜrbiəm/ i-TER-bee-əm
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	173.054(5)
Electron configuration	[Xe] 4f14 6s2
Electrons per shell	2, 8, 18, 32, 8, 2 (Image)
Physical properties
Phase	solid
Density (near r.t.)	6.90 g·cm−3
Liquid density at m.p.	6.21 g·cm−3
Melting point	1097 K, 824 °C, 1515 °F
Boiling point	1469 K, 1196 °C, 2185 °F
Heat of fusion	7.66 kJ·mol−1
Heat of vaporization	159 kJ·mol−1
Molar heat capacity	26.74 J·mol−1·K−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 736 813 910 1047 (1266) (1465)
Atomic properties
Oxidation states	3, 2 (basic oxide)
Electronegativity	? 1.1 (Pauling scale)
Ionization energies	1st: 603.4 kJ·mol−1
	2nd: 1174.8 kJ·mol−1
	3rd: 2417 kJ·mol−1
Atomic radius	176 pm
Covalent radius	187±8 pm
Miscellanea
Crystal structure	face-centered cubic
Magnetic ordering	paramagnetic[1]
Electrical resistivity	(r.t.) (β, poly) 0.250 µΩ·m
Thermal conductivity	38.5 W·m−1·K−1
Thermal expansion	(r.t.) (β, poly) 26.3 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 1590 m·s−1
Young's modulus	(β form) 23.9 GPa
Shear modulus	(β form) 9.9 GPa
Bulk modulus	(β form) 30.5 GPa
Poisson ratio	(β form) 0.207
Vickers hardness	206 MPa
Brinell hardness	343 MPa
CAS registry number	7440-64-4
Most stable isotopes
Main article: Isotopes of ytterbium
iso NA half-life DM DE (MeV) DP 166Yb syn 56.7 h ε 0.304 166Tm 168Yb 0.13% 168Yb is stable with 98 neutrons 169Yb syn 32.026 d ε 0.909 169Tm 170Yb 3.04% 170Yb is stable with 100 neutrons 171Yb 14.28% 171Yb is stable with 101 neutrons 172Yb 21.83% 172Yb is stable with 102 neutrons 173Yb 16.13% 173Yb is stable with 103 neutrons 174Yb 31.83% 174Yb is stable with 104 neutrons 175Yb syn 4.185 d β− 0.470 175Lu 176Yb 12.76% 176Yb is stable with 106 neutrons 177Yb syn 1.911 h β− 1.399 177Lu
v t e · r

Ytterbium ( /ɨˈtɜrbiəm/ i-TUR-bee-əm) is a chemical element with the symbol Yb and atomic number 70. A soft silvery metallic element, ytterbium is a rare earth element 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. Ytterbium-169, an artificially produced isotope, is used as a gamma ray source.

Characteristics

Physical properties

Ytterbium is a soft, malleable and ductile chemical element that displays a bright silvery luster when in its pure form. It is a rare earth element, and it is readily attacked and dissolved by the strong mineral acids. It reacts slowly with cold water and it oxidizes slowly in air.^[2]

Ytterbium has three allotropes labeled by the Greek letters alpha, beta and gamma; their transformation temperatures are −13 °C and 795 °C. The beta allotrope exists at room temperature, and it has a face-centered cubic crystal structure. The high-temperature gamma allotrope has a body-centered cubic crystalline structure.^[2]

Normally, the beta allotrope has a metallic electrical conductivity, but it becomes a semiconductor when exposed to a pressure of about 16,000 atmospheres (1.6 GPa). Its electrical resistivity 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).^[2][3]

In contrast with the other rare-earth metals, which usually have antiferromagnetic and/or ferromagnetic properties at low temperatures, ytterbium is paramagnetic at any temperatures above 1.0 kelvin.^[4]

With a melting point of 824 °C and a boiling point of 1196 °C ytterbium has a smaller range of liquid temperatures than any other metal.

Chemical properties

Ytterbium metal tarnishes slowly in air and burns readily at 200 °C to form ytterbium(III) oxide (Yb₂O₃) or less stable ytterbium monoxide (YbO).

Ytterbium is quite electropositive, and it reacts slowly with cold water and quite quickly with hot water to form ytterbium hydroxide:

2 Yb (s) + 6 H₂O (l) → 2 Yb(OH)₃ (aq) + 3 H₂ (g)

Ytterbium reacts with all the halogens:

2 Yb (s) + 3 F₂ (g) → 2 YbF₃ (s) [white]

2 Yb (s) + 3 Cl₂ (g) → 2 YbCl₃ (s) [white]

2 Yb (s) + 3 Br₂ (g) → 2 YbBr₃ (s) [white]

2 Yb (s) + 3 I₂ (g) → 2 YbI₃ (s) [white]

The ytterbium(III) ion absorbs light in the near infrared range of wavelengths, but not in visible light, so that the mineral ytterbia, Yb₂O₃, is white in color, and the salts of ytterbium of colorless anions are also colorless. Ytterbium dissolves readily in dilute sulfuric acid to form solutions that contain the colorless Yb(III) ions, which exist as a [Yb(OH₂)₉]³⁺ complexes:^[5]

2 Yb (s) + 3 H₂SO₄ (aq) → 2 Yb³⁺ (aq) + 3 SO2−
4 (aq) + 3 H₂ (g)

Chemical compounds

The chemical behavior of ytterbium is similar to that of the rest of the lanthanides. Most ytterbium compounds are found in the oxidation state +3, and its salts in this oxidation state are nearly colorless. Like europium, samarium, and thulium, the trihalogens of ytterbium can be reduced by hydrogen or by the addition of the metal reduced to the dihalogens, in this case the for example YbCl₂. The oxidation state +2 reacts in some ways similarly to the alkaline earth metal compounds, for example the Ytterbium(II) oxide (YbO) shows the same structure as calcium oxide (CaO).^[6]

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

• hydroxide: ytterbium hydroxide, Yb(OH)₃

Isotopes

Natural ytterbium is composed of seven stable isotopes: ¹⁶⁸Yb, ¹⁷⁰Yb, ¹⁷¹Yb, ¹⁷²Yb, ¹⁷³Yb, ¹⁷⁴Yb, and ¹⁷⁶Yb, with ¹⁷⁴Yb being the most abundant isotope, at 31.8% of the natural abundance). 27 radioisotopes have been observed, with the most stable ones being Yb-169 with a half-life of 32.0 days, ¹⁷⁵Yb with a half-life of 4.18 days, and ¹⁶⁶Yb with a half-life of 56.7 hours. All of its remaining radioactive isotopes have half-lives that are less than two hours, and the majority of these have half-lives that are less than 20 minutes. Ytterbium 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 atomic mass unit (u) for ¹⁴⁸Yb to 180.9562 u for ¹⁸¹Yb. Its primary decay mode at weights lower than the most abundant stable isotope, ¹⁷⁴Yb, is electron capture, and the primary decay mode above the atomic mass number of 174 is beta decay. The primary decay products at atomic masses lower than 174 are thulium isotopes, and the primary products from above 174 u are element (lutetium isotopes. Interestingly in modern quantum optics, the different isotopes of ytterbium follow either Bose-Einstein statistics or Fermi-Dirac statistics, leading to significant behavior in optical lattices.

History

Ytterbium was discovered by the Swiss chemist Jean Charles Galissard de Marignac in the year 1878. Marignac found a new component in the earth then known as erbia, and he named it ytterbia, for Ytterby, 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".^[3]

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. Carl Auer von Welsbach independently isolated these elements from ytterbia at about the same time, but he called them aldebaranium and cassiopeium.^[3]

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 using ion-exchange processes.^[3] The price of ytterbium was relatively stable between 1953 and 1998 at about US$ 1,000/kg.^[7]

Occurrence

Euxenite

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. The main mining areas are China, the United States, Brazil, India, Sri Lanka, and Australia; and reserves of ytterbium are estimated as one million tonnes. 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 and have not yet been well characterized. The abundance of ytterbium in the Earth crust is about 3 mg/kg.^[3]

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. The world production of ytterbium is only about 50 tonnes per year, reflecting the fact that ytterbium has few commercial applications.^[3] Microscopic traces of ytterbium are used as a dopant in the ytterbium YAG laser, or Yb:YAG laser, a solid-state laser in which ytterbium is the element that undergoes stimulated emission of electromagnetic radiation.

Production

Recovery of ytterbium from ores involves several processes which are common to most rare-earth elements: 1) processing, 2) separation of Yb from other rare earths, 3) preparation of the metal. If the starting ore is gadolinite, it is digested with hydrochloric or nitric acid which dissolves the rare-earth metals. The solution is treated with sodium oxalate or oxalic acid to precipitate rare earths as oxalates. For euxenite, ore is processed either by fusion with potassium bisulfate or with hydrofluoric acid. Monazite or xenotime are heated either with sulfuric acid or with caustic soda.

Ytterbium is separated from other rare earths either by ion 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 with hydrochloric acid. The metal is extracted from the solution as oxalate and converted to oxide by heating. The oxide is reduced to metal by heating with lanthanum, aluminium, cerium or zirconium in high vacuum. The metal is purified by sublimation and collected over a condensed plate.^[8]

Applications

Source of gamma 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. Experiment shows that radiographs taken with ¹⁶⁹Yb source are roughly equivalent to those taken with X-rays having energies between 250 and 350 keV.^[9]

Doping of stainless steel

Ytterbium can also be used as a dopant to help improve the grain refinement, strength, and other mechanical properties of stainless steel. Some ytterbium alloys have rarely been used in dentistry.^[2][3]

Yb as dopant of active media

Yb is used as dopant in optical 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.^[10]

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 1.06–1.12 µm band being optically pumped at wavelength 900 nm–1 µm, dependently on the host and application. Small quantum defect makes Yb prospective dopant for efficient lasers and power scaling.^[11]

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,^[10][12][13] although the application to the Yb-doped composite materials was under discussion.^[14][15]

Usually, low concentrations of Yb are used. At high concentration of excitations, the Yb-doped materials show photodarkening^[16] (glass fibers) or ever switch to the broadband emission ^[17] (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.^[18]

Others

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.^[19]

Due to the fact that lightwaves vibrate faster than microwaves, optical clocks can be more precise than the caesium atomic clocks which presently determine time. The Physikalisch-Technische Bundesanstalt (PTB) is working on several of such optical clocks simultaneously. The model with one single ytterbium ion caught in an ion trap is now experiencing another increase in accuracy. At PTB, scientists have succeeded in a transition of this ion and in measuring it with extreme accuracy. The optical clock based on it is exact to 17 digits after the decimal point.^[20]

Precautions

Although ytterbium is fairly stable chemically, it should be stored in air-tight containers and in an inert atmosphere to protect the metal from air and moisture. All compounds of ytterbium should be treated as highly toxic although initial studies appear to indicate that the danger is minimal. Ytterbium compounds are, however, known to cause irritation to the skin and eye, and some might be teratogenic.^[21] Metallic ytterbium dust poses a fire and explosion hazard.^[22]

References

Further reading

• Guide to the Elements – Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1

External links

Wikimedia Commons has media related to: Ytterbium

Look up ytterbium in Wiktionary, the free dictionary.

• WebElements.com – Ytterbium (also used as a reference)
• It's Elemental – Ytterbium