======================================================================
= Ytterbium =
======================================================================
Introduction
======================================================================
Ytterbium is a chemical element; it has symbol Yb and atomic number
70. It is a metal, the fourteenth and penultimate element in the
lanthanide series, which is the basis of the relative stability of its
+2 oxidation state. Like the other lanthanides, its most common
oxidation state is +3, as in its oxide, halides, and other compounds.
In aqueous 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 chemist Jean Charles Galissard de Marignac separated
from the rare earth "erbia", another independent component, which he
called "ytterbia", for Ytterby, the village in Sweden near where he
found the new component of erbium. He suspected that ytterbia was a
compound of a new element that he called "ytterbium". Four elements
were named after the village, the others being yttrium, terbium, and
erbium. In 1907, the new earth "lutecia" was separated from ytterbia,
from which the element "lutecium", now lutetium, was extracted by
Georges Urbain, Carl Auer von Welsbach, and Charles 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 a dopant of stainless steel or active
laser media, and less often as a gamma ray source.
Natural ytterbium is a mixture of seven stable isotopes, which
altogether are present at an average concentration of 0.3 parts per
million in the Earth's crust. This element is mined in China, the
United States, Brazil, and India in form of the minerals monazite,
euxenite, and xenotime. The ytterbium concentration is low because it
is found only among many other rare-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.
Physical properties
=====================
Ytterbium is a soft, malleable and ductile chemical element. When
freshly prepared, it is less golden than cesium. It is a rare-earth
element, and it is readily dissolved by the strong mineral acids.
Ytterbium has three allotropes labeled by the Greek letters alpha,
beta and gamma. Their transformation temperatures are −13 °C and 795
°C, although the exact transformation temperature depends on the
pressure and stress. The beta allotrope (6.966 g/cm3) exists at room
temperature, and it has a face-centered cubic crystal structure. The
high-temperature gamma allotrope (6.57 g/cm3) has a body-centered
cubic crystalline structure. The alpha allotrope (6.903 g/cm3) has a
hexagonal crystalline structure and is stable at low temperatures.
The beta allotrope has a metallic electrical conductivity at normal
atmospheric pressure, 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).
In contrast to the other rare-earth metals, which usually have
antiferromagnetic and/or ferromagnetic properties at low temperatures,
ytterbium is paramagnetic at temperatures above 1.0 kelvin. However,
the alpha allotrope is diamagnetic. With a melting point of 824 °C and
a boiling point of 1196 °C, ytterbium has the smallest liquid range of
all the metals.
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)
and lutetium (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 for metallic
bonding (in contrast to the other lanthanides where three electrons
are available) and increases ytterbium's metallic radius.
Chemical properties
=====================
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 with polytetrafluoroethylene or
hexachloroethane burn with an emerald-green flame. Ytterbium reacts
with hydrogen to form various non-stoichiometric hydrides. Ytterbium
dissolves slowly in water, but quickly in acids, liberating hydrogen.
Ytterbium is quite electropositive, and it reacts slowly with cold
water and quite quickly with hot water to form ytterbium(III)
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 (l) → 2 YbBr3 (s) [white]
:2 Yb (s) + 3 I2 (s) → 2 YbI3 (s) [white]
The ytterbium(III) ion absorbs light in the near-infrared range of
wavelengths, but not in visible light, so ytterbia, Yb2O3, is white in
color and the salts of ytterbium are also colorless. Ytterbium
dissolves readily in dilute sulfuric acid to form solutions that
contain the colorless Yb(III) ions, which exist as nonahydrate
complexes:
:2 Yb (s) + 3 H2SO4 (aq) + 18 (l) → 2 [Yb(H2O)9]3+ (aq) + 3 (aq) + 3
H2 (g)
Yb(II) vs. Yb(III)
====================
Although usually trivalent, ytterbium readily forms divalent
compounds. This behavior is unusual for lanthanides, which almost
exclusively form compounds with an oxidation state of +3. The +2 state
has a valence electron configuration of 4'f'14 because the fully
filled 'f'-shell gives more stability. The yellow-green ytterbium(II)
ion is a very strong reducing agent and decomposes water, releasing
hydrogen, and thus only the colorless ytterbium(III) ion occurs in
aqueous solution. Samarium and thulium also behave this way in the +2
state, but europium(II) is stable in aqueous solution. Ytterbium metal
behaves similarly to europium metal and the alkaline earth metals,
dissolving in ammonia to form blue electride salts.
Isotopes
==========
Natural ytterbium is composed of seven stable isotopes: 168Yb, 170Yb,
171Yb, 172Yb, 173Yb, 174Yb, and 176Yb, with 174Yb being the most
common, at 31.8% of the natural abundance). Thirty-two radioisotopes
have been observed, with the most stable ones being 169Yb 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 the remaining radioactive
isotopes have half-lives that are less than two hours, and most of
these have half-lives under 20 minutes. Ytterbium also has 12 meta
states, with the most stable being 169mYb ('t'1/2 46 seconds).
The isotopes of ytterbium range from 149Yb to 187Yb. The primary decay
mode of ytterbium isotopes lighter than the most abundant stable
isotope, 174Yb, is electron capture, and the primary decay mode for
those heavier than 174Yb is beta decay. The primary decay products of
ytterbium isotopes lighter than 174Yb are thulium isotopes, and the
primary decay products of ytterbium isotopes with heavier than 174Yb
are lutetium isotopes.
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.
The main mining areas are China, the United States, Brazil, India, Sri
Lanka, and Australia. 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.
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.
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 that it has few commercial
applications. Microscopic traces of ytterbium are used as a dopant in
the Yb:YAG laser, a solid-state laser in which ytterbium is the
element that undergoes stimulated emission of electromagnetic
radiation.
Ytterbium is often the most common substitute in yttrium minerals. In
very few known cases/occurrences ytterbium prevails over yttrium, as,
e.g., in xenotime-(Yb). A report of native ytterbium from the Moon's
regolith is known.
Production
======================================================================
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 as monazite or xenotime are
dissolved into various acids, such as sulfuric acid. Ytterbium can
then be separated from other lanthanides by ion exchange, as can other
lanthanides. The solution is then applied to a resin, to which
different lanthanides bind with different affinities. This is then
dissolved using complexing agents, and due to the different types of
bonding exhibited by the different lanthanides, it is possible to
isolate the compounds.
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.
Compounds
======================================================================
The chemical behavior of ytterbium is similar to that of the rest of
the lanthanides. Most ytterbium compounds are found in the +3
oxidation state, and its salts in this oxidation state are nearly
colorless. Like europium, samarium, and thulium, the trihalides of
ytterbium can be reduced to the dihalides by hydrogen, zinc dust, or
by the addition of metallic ytterbium. The +2 oxidation state occurs
only in solid compounds and reacts in some ways similarly to the
alkaline earth metal compounds; for example, ytterbium(II) oxide (YbO)
shows the same structure as calcium oxide (CaO).
Halides
=========
Ytterbium forms both dihalides and trihalides with the halogens
fluorine, chlorine, bromine, and iodine. The dihalides are susceptible
to oxidation to the trihalides at room temperature and
disproportionate to the trihalides and metallic ytterbium at high
temperature:
:3 YbX2 → 2 YbX3 + Yb (X = F, Cl, Br, I)
Some ytterbium halides are used as reagents in organic synthesis. For
example, ytterbium(III) chloride (YbCl3) is a Lewis acid and can be
used as a catalyst in the Aldol and Diels-Alder reactions.
Ytterbium(II) iodide (YbI2) may be used, like samarium(II) iodide, as
a reducing agent for coupling reactions. Ytterbium(III) fluoride
(YbF3) is used as an inert and non-toxic tooth filling as it
continuously releases fluoride ions, which are good for dental health,
and is also a good X-ray contrast agent.
Oxides
========
Ytterbium reacts with oxygen to form ytterbium(III) oxide (Yb2O3),
which crystallizes in the "rare-earth C-type sesquioxide" structure
which is related to the fluorite structure with one quarter of the
anions removed, leading to ytterbium atoms in two different six
coordinate (non-octahedral) environments. Ytterbium(III) oxide can be
reduced to ytterbium(II) oxide (YbO) with elemental ytterbium, which
crystallizes in the same structure as sodium chloride.
Borides
=========
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 a Kondo insulator. It is a
quantum material; under normal conditions, the interior of the bulk
crystal is an insulator whereas the surface is highly conductive.
Among the rare earth elements, ytterbium is one of the few that can
form a stable dodecaboride, a property attributed to its comparatively
small atomic radius.
History
======================================================================
In 1878, Ytterbium was discovered by the Swiss chemist Jean Charles
Galissard de Marignac. While examining samples of gadolinite, 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".
In 1907, the French chemist Georges Urbain separated Marignac's
ytterbia into two components: 'neoytterbia' and 'lutecia'. Neoytterbia
later became known as the element ytterbium, and lutecia became known
as the element lutetium. The Austrian chemist Carl Auer von Welsbach
independently isolated these elements from ytterbia at about the same
time, but he called them 'aldebaranium' ('Ad'; after Aldebaran) and
'cassiopeium'. The American chemist Charles James also independently
isolated these elements at about the same time.
Urbain and Welsbach accused each other of publishing results based on
the other party. In 1909, the Commission on Atomic Mass, consisting of
Frank 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. After Urbain's
names were recognized, 'neoytterbium' was reverted to 'ytterbium'.
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. The
price of ytterbium was relatively stable between 1953 and 1998 at
about US$1,000/kg.
Source of gamma rays
======================
The 169Yb isotope (with a half-life of 32 days), which is created
along with the short-lived 175Yb isotope (half-life 4.2 days) by
neutron activation during the irradiation of ytterbium in nuclear
reactors, has been used as a radiation source in portable X-ray
machines. Like X-rays, the gamma rays emitted by the source 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.
Experiments show that radiographs taken with a 169Yb source are
roughly equivalent to those taken with X-rays having energies between
250 and 350 keV. 169Yb is also used in nuclear medicine.
High-stability atomic clocks
==============================
In 2013, a pair of experimental atomic clocks based on ytterbium atoms
at the National 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 1 quintillion (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 atoms
laser-cooled to 10 microkelvin (10 millionths of a degree above
absolute zero) and trapped in an optical 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.
Visible light waves oscillate faster than microwaves, hence optical
clocks can be more precise than caesium atomic clocks. The
Physikalisch-Technische Bundesanstalt is working on several such
optical clocks. The model with one single ytterbium ion caught in an
ion trap is highly accurate. The optical clock based on it is exact to
17 digits after the decimal point.
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.
Ytterbium as dopant of active media
=====================================
The Yb3+ ion is used as a doping material in active laser media,
specifically in solid state lasers and double 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. Ytterbium lasers commonly radiate
in the 1.03-1.12 μm band being optically pumped at wavelength 900 nm-1
μm, dependently on the host and application. The small quantum defect
makes ytterbium a prospective dopant for efficient lasers and power
scaling.
The kinetic of excitations in ytterbium-doped materials is simple and
can be described within the concept of effective cross-sections; for
most ytterbium-doped laser materials (as for many other optically
pumped gain media), the McCumber relation holds,
although the application to the ytterbium-doped composite materials
was under discussion.
Usually, low concentrations of ytterbium are used. At high
concentrations, the ytterbium-doped materials show photodarkening
(glass fibers) or even a switch to broadband emission (crystals and
ceramics) instead of efficient laser action. This effect may be
related with not only overheating, but also with conditions of charge
compensation at high concentrations of ytterbium ions.
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. Ytterbium-doped LMA fibers also have the
advantages of a larger mode field diameter, which negates the impacts
of nonlinear effects such as stimulated Brillouin scattering and
stimulated Raman 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. 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.
Ion qubits for quantum computing
==================================
The charged ion 171Yb+ is used by multiple academic groups and
companies as the trapped-ion qubit for quantum computing. Entangling
gates, such as the Mølmer-Sørensen gate, have been achieved by
addressing the ions with mode-locked pulse lasers.
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.
Currently, ytterbium is being investigated as a possible replacement
for magnesium in high density pyrotechnic payloads for kinematic
infrared decoy flares. As ytterbium(III) oxide has a significantly
higher emissivity in the infrared range than magnesium oxide, a higher
radiant intensity is obtained with ytterbium-based payloads in
comparison to those commonly based on magnesium/Teflon/Viton (MTV).
Precautions
======================================================================
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. All
compounds of ytterbium are treated as highly toxic, although studies
appear to indicate that the danger is minimal. However, ytterbium
compounds cause irritation to human skin and eyes, and some might be
teratogenic. Metallic ytterbium dust can spontaneously combust.
Further reading
======================================================================
*'Guide to the Elements - Revised Edition', Albert Stwertka, (Oxford
University Press; 1998)
External links
======================================================================
*[
http://education.jlab.org/itselemental/ele070.html It's Elemental -
Ytterbium]
*
*
[
https://link.springer.com/referenceworkentry/10.1007%2F978-3-319-39193-9_144-2
Encyclopedia of Geochemistry - Ytterbium]
License
=========
All content on Gopherpedia comes from Wikipedia, and is licensed under CC-BY-SA
License URL:
http://creativecommons.org/licenses/by-sa/3.0/
Original Article:
http://en.wikipedia.org/wiki/Ytterbium
