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= Samarium =
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Introduction
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Samarium is a chemical element; it has symbol Sm and atomic number 62.
It is a moderately hard silvery metal that slowly oxidizes in air.
Being a typical member of the lanthanide series, samarium usually has
the oxidation state +3. Compounds of samarium(II) are also known, most
notably the monoxide SmO, monochalcogenides SmS, SmSe and SmTe, as
well as samarium(II) iodide.
Discovered in 1879 by French chemist Paul-Émile Lecoq de Boisbaudran,
samarium was named after the mineral samarskite from which it was
isolated. The mineral itself was named after a Russian mine official,
Colonel Vassili Samarsky-Bykhovets, who thus became the first person
to have a chemical element named after him, though the name was
indirect.
Samarium occurs in concentration up to 2.8% in several minerals
including cerite, gadolinite, samarskite, monazite and bastnäsite, the
last two being the most common commercial sources of the element.
These minerals are mostly found in China, the United States, Brazil,
India, Sri Lanka and Australia; China is by far the world leader in
samarium mining and production.
The main commercial use of samarium is in samarium-cobalt magnets,
which have permanent magnetization second only to neodymium magnets;
however, samarium compounds can withstand significantly higher
temperatures, above 700 C, without losing their permanent magnetic
properties. The radioisotope samarium-153 is the active component of
the drug samarium (153Sm) lexidronam (Quadramet), which kills cancer
cells in lung cancer, prostate cancer, breast cancer and osteosarcoma.
Another isotope, samarium-149, is a strong neutron absorber and so is
added to control rods of nuclear reactors. It also forms as a decay
product during reactor operation and is one of the important factors
considered in reactor design and operation. Other uses of samarium
include catalysis of chemical reactions, radioactive dating and X-ray
lasers. Samarium(II) iodide, in particular, is a common reducing agent
in chemical synthesis.
Samarium has no biological role; some samarium salts are slightly
toxic.
Physical properties
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Samarium is a rare earth element with a hardness and density similar
to zinc. With a boiling point of 1794 C, samarium is the third most
volatile lanthanide after ytterbium and europium and comparable in
this respect to lead and barium; this helps separation of samarium
from its ores. When freshly prepared, samarium has a silvery lustre,
and takes on a duller appearance when oxidized in air. Samarium is
calculated to have one of the largest atomic radii of the elements;
with a radius of 238 pm, only potassium, praseodymium, barium,
rubidium and caesium are larger.
In ambient conditions, samarium has a rhombohedral structure (α form).
Upon heating to 731 C, its crystal symmetry changes to hexagonal
close-packed ('hcp'),; it has actual transition temperature depending
on metal purity. Further heating to 922 C transforms the metal into a
body-centered cubic ('bcc') phase. Heating to 300 C plus compression
to 40 kbar results in a double-hexagonally close-packed structure
('dhcp'). Higher pressure of the order of hundreds or thousands of
kilobars induces a series of phase transformations, in particular with
a tetragonal phase appearing at about 900 kbar. In one study, the
'dhcp' phase could be produced without compression, using a
nonequilibrium annealing regime with a rapid temperature change
between about 400 C and 700 C, confirming the transient character of
this samarium phase. Thin films of samarium obtained by vapor
deposition may contain the 'hcp' or 'dhcp' phases in ambient
conditions.
Samarium and its sesquioxide are paramagnetic at room temperature.
Their corresponding effective magnetic moments, below 2 bohr
magnetons, are the third-lowest among lanthanides (and their oxides)
after lanthanum and lutetium. The metal transforms to an
antiferromagnetic state upon cooling to 14.8 K. Individual samarium
atoms can be isolated by encapsulating them into fullerene molecules.
They can also be intercalated into the interstices of the bulk C60 to
form a solid solution of nominal composition Sm3C60, which is
superconductive at a temperature of 8 K. Samarium doping of iron-based
superconductors - a class of high-temperature superconductor -
increases their transition to normal conductivity temperature up to 56
K, the highest value achieved so far in this series.
Chemical properties
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In air, samarium slowly oxidizes at room temperature and spontaneously
ignites at 150 C. Even when stored under mineral oil, samarium
gradually oxidizes and develops a grayish-yellow powder of the
oxide-hydroxide mixture at the surface. The metallic appearance of a
sample can be preserved by sealing it under an inert gas such as
argon.
Samarium is quite electropositive and reacts slowly with cold water
and rapidly with hot water to form samarium hydroxide:
: {{chem2|2Sm_{(s)} + 6H2O_{(l)} → 2Sm(OH)3_{(aq)} + 3H2_{(g)}|}}
Samarium dissolves readily in dilute sulfuric acid to form solutions
containing the yellow to pale green Sm(III) ions, which exist as
complexes:
: {{chem2|2Sm_{(s)} + 3H2SO4_{(aq)} → 2Sm(3+)_{(aq)} + 3SO4(2-)_{(aq)}
+ 3H2_{(g)}|}}
Samarium is one of the few lanthanides with a relatively accessible +2
oxidation state, alongside Eu and Yb. ions are blood-red in aqueous
solution.
Compounds
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Formula Color Symmetry Space group No. Pearson symbol 'a' (pm) 'b'
(pm) 'c' (pm) 'Z' Density, g/cm3
Sm silvery trigonal Rm 166 hR9 362.9 362.9 2621.3 9 7.52
Sm silvery hexagonal P63/mmc 194 hP4 362 362 1168 4 7.54
Sm silvery tetragonal I4/mmm 139 tI2 240.2 240.2 423.1 2 20.46
SmO golden cubic Fmm 225 cF8 494.3 494.3 494.3 4 9.15
Sm2O3 trigonal Pm1 164 hP5 377.8 377.8 594 1 7.89
Sm2O3 monoclinic C2/m 12 mS30 1418 362.4 885.5 6 7.76
Sm2O3 cubic Ia 206 cI80 1093 1093 1093 16 7.1
SmH2 cubic Fmm 225 cF12 537.73 537.73 537.73 4 6.51
SmH3 hexagonal Pc1 165 hP24 377.1 377.1 667.2 6
Sm2B5 gray monoclinic P21/c 14 mP28 717.9 718 720.5 4 6.49
SmB2 hexagonal P6/mmm 191 hP3 331 331 401.9 1 7.49
SmB4 tetragonal P4/mbm 127 tP20 717.9 717.9 406.7 4 6.14
SmB6 cubic Pmm 221 cP7 413.4 413.4 413.4 1 5.06
SmB66 cubic Fmc 226 cF1936 2348.7 2348.7 2348.7 24 2.66
Sm2C3 cubic I3d 220 cI40 839.89 839.89 839.89 8 7.55
SmC2 tetragonal I4/mmm 139 tI6 377 377 633.1 2 6.44
SmF2 purple cubic Fmm 225 cF12 587.1 587.1 587.1 4 6.18
SmF3 white orthorhombic Pnma 62 oP16 667.22 705.85 440.43 4 6.64
SmCl2 brown orthorhombic Pnma 62 oP12 756.28 450.77 901.09 4 4.79
SmCl3 yellow hexagonal P63/m 176 hP8 737.33 737.33 416.84 2 4.35
SmBr2 brown orthorhombic Pnma 62 oP12 797.7 475.4 950.6 4 5.72
SmBr3 yellow orthorhombic Cmcm 63 oS16 404 1265 908 2 5.58
SmI2 green monoclinic P21/c 14 mP12
SmI3 orange trigonal R 63 hR24 749 749 2080 6 5.24
SmN cubic Fmm 225 cF8 357 357 357 4 8.48
SmP cubic Fmm 225 cF8 576 576 576 4 6.3
SmAs cubic Fmm 225 cF8 591.5 591.5 591.5 4 7.23
Oxides
========
The most stable oxide of samarium is the sesquioxide Sm2O3. Like many
samarium compounds, it exists in several crystalline phases. The
trigonal form is obtained by slow cooling from the melt. The melting
point of Sm2O3 is high (2345 °C), so it is usually melted not by
direct heating, but with induction heating, through a radio-frequency
coil. Sm2O3 crystals of monoclinic symmetry can be grown by the flame
fusion method (Verneuil process) from Sm2O3 powder, that yields
cylindrical boules up to several centimeters long and about one
centimeter in diameter. The boules are transparent when pure and
defect-free and are orange otherwise. Heating the metastable trigonal
Sm2O3 to 1900 C converts it to the more stable monoclinic phase. Cubic
Sm2O3 has also been described.
Samarium is one of the few lanthanides that form a monoxide, SmO. This
lustrous golden-yellow compound was obtained by reducing Sm2O3 with
samarium metal at high temperature (1000 °C) and a pressure above 50
kbar; lowering the pressure resulted in incomplete reaction. SmO has
cubic rock-salt lattice structure.
Chalcogenides
===============
Samarium forms a trivalent sulfide, selenide and telluride. Divalent
chalcogenides SmS, SmSe and SmTe with a cubic rock-salt crystal
structure are known. These chalcogenides convert from a semiconducting
to metallic state at room temperature upon application of pressure.
Whereas the transition is continuous and occurs at about 20-30 kbar in
SmSe and SmTe, it is abrupt in SmS and requires only 6.5 kbar. This
effect results in a spectacular color change in SmS from black to
golden yellow when its crystals of films are scratched or polished.
The transition does not change the lattice symmetry, but there is a
sharp decrease (~15%) in the crystal volume. It exhibits hysteresis,
i.e., when the pressure is released, SmS returns to the semiconducting
state at a much lower pressure of about 0.4 kbar.
Halides
=========
Samarium metal reacts with all the halogens, forming trihalides:
:2 Sm (s) + 3 X2 (g) → 2 SmX3 (s) (X = F, Cl, Br or I)
Their further reduction with samarium, lithium or sodium metals at
elevated temperatures (about 700-900 °C) yields the dihalides. The
diiodide can also be prepared by heating SmI3, or by reacting the
metal with 1,2-diiodoethane in anhydrous tetrahydrofuran at room
temperature:
:Sm (s) + ICH2-CH2I → SmI2 + CH2=CH2.
In addition to dihalides, the reduction also produces many
non-stoichiometric samarium halides with a well-defined crystal
structure, such as Sm3F7, Sm14F33, Sm27F64, Sm11Br24, Sm5Br11 and
Sm6Br13.
Samarium halides change their crystal structures when one type of
halide anion is substituted for another, which is an uncommon behavior
for most elements (e.g. actinides). Many halides have two major
crystal phases for one composition, one being significantly more
stable and another being metastable. The latter is formed upon
compression or heating, followed by quenching to ambient conditions.
For example, compressing the usual monoclinic samarium diiodide and
releasing the pressure results in a PbCl2-type orthorhombic structure
(density 5.90 g/cm3), and similar treatment results in a new phase of
samarium triiodide (density 5.97 g/cm3).
Borides
=========
Sintering powders of samarium oxide and boron, in a vacuum, yields a
powder containing several samarium boride phases; the ratio between
these phases can be controlled through the mixing proportion. The
powder can be converted into larger crystals of samarium borides using
arc melting or zone melting techniques, relying on the different
melting/crystallization temperature of SmB6 (2580 °C), SmB4 (about
2300 °C) and SmB66 (2150 °C). All these materials are hard, brittle,
dark-gray solids with the hardness increasing with the boron content.
Samarium diboride is too volatile to be produced with these methods
and requires high pressure (about 65 kbar) and low temperatures
between 1140 and 1240 °C to stabilize its growth. Increasing the
temperature results in the preferential formation of SmB6.
Samarium hexaboride
=====================
Samarium hexaboride is a typical intermediate-valence compound where
samarium is present both as Sm2+ and Sm3+ ions in a 3:7 ratio. It
belongs to a class of Kondo insulators; at temperatures above 50 K,
its properties are typical of a Kondo metal, with metallic electrical
conductivity characterized by strong electron scattering, whereas at
lower temperatures, it behaves as a non-magnetic insulator with a
narrow band gap of about 4-14 meV. The cooling-induced metal-insulator
transition in SmB6 is accompanied by a sharp increase in the thermal
conductivity, peaking at about 15 K. The reason for this increase is
that electrons themselves do not contribute to the thermal
conductivity at low temperatures, which is dominated by phonons, but
the decrease in electron concentration reduces the rate of
electron-phonon scattering.
Other inorganic compounds
===========================
Samarium carbides are prepared by melting a graphite-metal mixture in
an inert atmosphere. After the synthesis, they are unstable in air and
need to be studied under an inert atmosphere. Samarium monophosphide
SmP is a semiconductor with a bandgap of 1.10 eV, the same as in
silicon, and electrical conductivity of n-type. It can be prepared by
annealing at 1100 C an evacuated quartz ampoule containing mixed
powders of phosphorus and samarium. Phosphorus is highly volatile at
high temperatures and may explode, thus the heating rate has to be
kept well below 1 °C/min. A similar procedure is adopted for the
monarsenide SmAs, but the synthesis temperature is higher at 1800 C.
Numerous crystalline binary compounds are known for samarium and one
of the group 14, 15, or 16 elements X, where X is Si, Ge, Sn, Pb, Sb
or Te, and metallic alloys of samarium form another large group. They
are all prepared by annealing mixed powders of the corresponding
elements. Many of the resulting compounds are non-stoichiometric and
have nominal compositions SmaXb, where the b/a ratio varies between
0.5 and 3.
Organometallic compounds
==========================
Samarium forms a cyclopentadienide and its chloroderivatives and .
They are prepared by reacting samarium trichloride with in
tetrahydrofuran. Contrary to cyclopentadienides of most other
lanthanides, in some rings bridge each other by forming ring
vertexes η1 or edges η2 toward another neighboring samarium, thus
creating polymeric chains. The chloroderivative has a dimer
structure, which is more accurately expressed as . There, the chlorine
bridges can be replaced, for instance, by iodine, hydrogen or nitrogen
atoms or by CN groups.
The ()− ion in samarium cyclopentadienides can be replaced by the
indenide ()− or cyclooctatetraenide ()2− ring, resulting in or . The
latter compound has a structure similar to uranocene. There is also a
cyclopentadienide of divalent samarium, a solid that sublimates at
about 85 C. Contrary to ferrocene, the rings in are not parallel but
are tilted by 40°.
A metathesis reaction in tetrahydrofuran or ether gives alkyls and
aryls of samarium:
:
:{{chem2|Sm(OR)3 + 3LiCH(SiMe3)2 → Sm{CH(SiMe3)2}3 + 3LiOR}}
Here R is a hydrocarbon group and Me = methyl.
Isotopes
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Naturally occurring samarium is composed of five stable isotopes:
144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived
radioisotopes, 147Sm (half-life 't'1/2 = 1.06 years) and 148Sm (7
years), with 152Sm being the most abundant (26.75%). 149Sm is listed
by various sources as being stable, but some sources state that it is
radioactive, with a lower bound for its half-life given as years.
Some observationally stable samarium isotopes are predicted to decay
to isotopes of neodymium. The long-lived isotopes 146Sm, 147Sm, and
148Sm undergo alpha decay to neodymium isotopes. Lighter unstable
isotopes of samarium mainly decay by electron capture to promethium,
while heavier ones beta decay to europium. The known isotopes range
from 129Sm to 168Sm. The half-lives of 151Sm and 145Sm are 90 years
and 340 days, respectively. All remaining radioisotopes have
half-lives that are less than 2 days, and most these have half-life
less than 48 seconds. Samarium also has twelve known nuclear isomers,
the most stable of which are 141mSm (half-life 22.6 minutes), 143m1Sm
('t'1/2 = 66 seconds), and 139mSm ('t'1/2 = 10.7 seconds). Natural
samarium has a radioactivity of 127 Bq/g, mostly due to 147Sm, which
alpha decays to 143Nd with a half-life of 1.06 years and is used in
samarium-neodymium dating. 146Sm is an extinct radionuclide, with the
half-life of 9.20 years. There have been searches of samarium-146 as a
primordial nuclide, because its half-life is long enough such that
minute quantities of the element should persist today. It can be used
in radiometric dating.
Samarium-149 is an observationally stable isotope of samarium
(predicted to decay, but no decays have ever been observed, giving it
a half-life at least several orders of magnitude longer than the age
of the universe), and a product of the decay chain from the fission
product 149Nd (yield 1.0888%). 149Sm is a decay product and
neutron-absorber in nuclear reactors, with a neutron poison effect
that is second in importance for reactor design and operation only to
135Xe. Its neutron cross section is 41000 barns for thermal neutrons.
Because samarium-149 is not radioactive and is not removed by decay,
it presents problems somewhat different from those encountered with
xenon-135. The equilibrium concentration (and thus the poisoning
effect) builds to an equilibrium value during reactor operations in
about 500 hours (about three weeks), and since samarium-149 is stable,
its concentration remains essentially constant during reactor
operation.
Samarium-153 is a beta emitter with a half-life of 46.3 hours. It is
used to kill cancer cells in lung cancer, prostate cancer, breast
cancer, and osteosarcoma. For this purpose, samarium-153 is chelated
with ethylene diamine tetramethylene phosphonate (EDTMP) and injected
intravenously. The chelation prevents accumulation of radioactive
samarium in the body that would result in excessive irradiation and
generation of new cancer cells. The corresponding drug has several
names including samarium (153Sm) lexidronam; its trade name is
Quadramet.
History
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Detection of samarium and related elements was announced by several
scientists in the second half of the 19th century; however, most
sources give priority to French chemist Paul-Émile Lecoq de
Boisbaudran. Boisbaudran isolated samarium oxide and/or hydroxide in
Paris in 1879 from the mineral samarskite ) and identified a new
element in it via sharp optical absorption lines. Swiss chemist Marc
Delafontaine announced a new element 'decipium' (from meaning
"deceptive, misleading") in 1878, but later in 1880-1881 demonstrated
that it was a mix of several elements, one being identical to
Boisbaudran's samarium. Though samarskite was first found in the Ural
Mountains in Russia, by the late 1870s it had been found in other
places, making it available to many researchers. In particular, it was
found that the samarium isolated by Boisbaudran was also impure and
had a comparable amount of europium. The pure samarium(III) oxide was
produced only in 1901 by Eugène-Anatole Demarçay, and in 1903 Wilhelm
Muthmann isolated the element.
Boisbaudran named his element 'samarium' after the mineral samarskite,
which in turn honored Vassili Samarsky-Bykhovets (1803-1870).
Samarsky-Bykhovets, as the Chief of Staff of the Russian Corps of
Mining Engineers, had granted access for two German mineralogists, the
brothers Gustav and Heinrich Rose, to study the mineral samples from
the Urals. Samarium was thus the first chemical element to be named
after a person. The word 'samaria' is sometimes used to mean
samarium(III) oxide, by analogy with yttria, zirconia, alumina, ceria,
holmia, etc. The symbol 'Sm' was suggested for samarium, but an
alternative 'Sa' was often used instead until the 1920s.
Before the advent of ion-exchange separation technology in the 1950s,
pure samarium had no commercial uses. However, a by-product of
fractional crystallization purification of neodymium was a mix of
samarium and gadolinium that got the name "Lindsay Mix" after the
company that made it, and was used for nuclear control rods in some
early nuclear reactors. Nowadays, a similar commodity product has the
name "samarium-europium-gadolinium" (SEG) concentrate. It is prepared
by solvent extraction from the mixed lanthanides isolated from
bastnäsite (or monazite). Since heavier lanthanides have more affinity
for the solvent used, they are easily extracted from the bulk using
relatively small proportions of solvent. Not all rare-earth producers
who process bastnäsite do so on a large enough scale to continue by
separating the components of SEG, which typically makes up only 12% of
the original ore. Such producers therefore make SEG with a view to
marketing it to the specialized processors. In this manner, the
valuable europium in the ore is rescued for use in making phosphor.
Samarium purification follows the removal of the europium. , being in
oversupply, samarium oxide is cheaper on a commercial scale than its
relative abundance in the ore might suggest.
Occurrence and production
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Samarium concentration in soils varies between 2 and 23 ppm, and
oceans contain about 0.5-0.8 parts per trillion. The median value for
its abundance in the Earth's crust used by the CRC Handbook is 7parts
per million (ppm) and is the 40th most abundant element. Distribution
of samarium in soils strongly depends on its chemical state and is
very inhomogeneous: in sandy soils, samarium concentration is about
200 times higher at the surface of soil particles than in the water
trapped between them, and this ratio can exceed 1,000 in clays.
Samarium is not found free in nature, but, like other rare earth
elements, is contained in many minerals, including monazite,
bastnäsite, cerite, gadolinite and samarskite; monazite (in which
samarium occurs at concentrations of up to 2.8%) and bastnäsite are
mostly used as commercial sources. World resources of samarium are
estimated at two million tonnes; they are mostly located in China, US,
Brazil, India, Sri Lanka and Australia, and the annual production is
about 700 tonnes. Country production reports are usually given for all
rare-earth metals combined. By far, China has the largest production
with 120,000 tonnes mined per year; it is followed by the US (about
5,000 tonnes) and India (2,700 tonnes). Samarium is usually sold as
oxide, which at the price of about US$30/kg is one of the cheapest
lanthanide oxides. Whereas mischmetal - a mixture of rare earth metals
containing about 1% of samarium - has long been used, relatively pure
samarium has been isolated only recently, through ion exchange
processes, solvent extraction techniques, and electrochemical
deposition. The metal is often prepared by electrolysis of a molten
mixture of samarium(III) chloride with sodium chloride or calcium
chloride. Samarium can also be obtained by reducing its oxide with
lanthanum. The product is then distilled to separate samarium (boiling
point 1,794 °C) and lanthanum (b.p. 3,464 °C).
Very few minerals have samarium being the most dominant element.
Minerals with essential (dominant) samarium include monazite-(Sm) and
florencite-(Sm). These minerals are very rare and are usually found
containing other elements, usually cerium or neodymium. It is also
made by neutron capture by samarium-149, which is added to the control
rods of nuclear reactors. Therefore, (151)Sm is present in spent
nuclear fuel and radioactive waste.
Separating samarium from minerals involves nearly 100 individual
processes and extremely strong acids.
Geopolitics
=============
Western militaries across the world relied on a single samarium
production plant in La Rochelle, France from the 1970s until the
plant's closure in 1994. The facility sourced its samarium from
Australia. A $1billion United States government effort to re-open a
closed rare earths mine in Mountain Pass, California resulted in the
facility going bankrupt.
, China produces all of the world's usable samarium; refining is
concentrated in Baotou. The Biden administration signed two contracts
for samarium production plants in the United States, but neither
materialized. During US president Donald Trump's second-term tariff
war, China leveled strict limits on the export of samarium, among
other rare earth metals, as part of the long-running rare earths trade
dispute (and larger trade war) between the two nations.
Magnets
=========
An important use of samarium is samarium-cobalt magnets, which are
nominally or . They have high permanent magnetization, about 10,000
times that of iron and second only to neodymium magnets. However,
samarium magnets resist demagnetization better; they are stable to
temperatures above 700 C (cf. 300-400 °C for neodymium magnets). These
magnets are found in small motors, headphones, and high-end magnetic
pickups for guitars and related musical instruments. For example, they
are used in the motors of a solar-powered electric aircraft, the Solar
Challenger, and in the Samarium Cobalt Noiseless electric guitar and
bass pickups.
Due to their heat resistance, samarium magnets are also used for
military applications and are needed to manufacture modern aircraft
and missiles. A single F-35 fighter jet contains about of samarium
magnets.
Chemical reagent
==================
Samarium and its compounds are important as catalysts and chemical
reagents. Samarium catalysts help the decomposition of plastics,
dechlorination of pollutants such as polychlorinated biphenyls (PCB),
as well as dehydration and dehydrogenation of ethanol. Samarium(III)
triflate , that is , is one of the most efficient Lewis acid catalysts
for a halogen-promoted Friedel-Crafts reaction with alkenes.
Samarium(II) iodide is a very common reducing and coupling agent in
organic synthesis, for example in desulfonylation reactions;
annulation; Danishefsky, Kuwajima, Mukaiyama and Holton Taxol total
syntheses; strychnine total synthesis; Barbier reaction and other
reductions with samarium(II) iodide.
In its usual oxidized form, samarium is added to ceramics and glasses
where it increases absorption of infrared light. As a (minor) part of
mischmetal, samarium is found in the "flint" ignition devices of many
lighters and torches.
Neutron absorber
==================
Samarium-149 has a high cross section for neutron capture (41,000
barns) and so is used in control rods of nuclear reactors. Its
advantage compared to competing materials, such as boron and cadmium,
is stability of absorption - most of the fusion products of (149)Sm
are other isotopes of samarium that are also good neutron absorbers.
For example, the cross section of samarium-151 is 15,000 barns, it is
on the order of hundreds of barns for (150)Sm, (152)Sm, and (153)Sm,
and 6,800 barns for natural (mixed-isotope) samarium.
Lasers
========
Samarium-doped calcium fluoride crystals were used as an active medium
in one of the first solid-state lasers designed and built by Peter
Sorokin (co-inventor of the dye laser) and Mirek Stevenson at IBM
research labs in early 1961. This samarium laser gave pulses of red
light at 708.5 nm. It had to be cooled by liquid helium and so did not
find practical applications. Another samarium-based laser became the
first saturated X-ray laser operating at wavelengths shorter than 10
nanometers. It gave 50-picosecond pulses at 7.3 and 6.8 nm suitable
for uses in holography, high-resolution microscopy of biological
specimens, deflectometry, interferometry, and radiography of dense
plasmas related to confinement fusion and astrophysics. Saturated
operation meant that the maximum possible power was extracted from the
lasing medium, resulting in the high peak energy of 0.3 mJ. The active
medium was samarium plasma produced by irradiating samarium-coated
glass with a pulsed infrared Nd-glass laser (wavelength ~1.05 μm).
Storage phosphor
==================
In 2007 it was shown that nanocrystalline BaFCl:Sm(3+) as prepared by
co-precipitation can serve as a very efficient X-ray storage phosphor.
The co-precipitation leads to nanocrystallites of the order of 100-200
nm in size and their sensitivity as X-ray storage phosphors is
increased a remarkable ~500,000 times because of the specific
arrangements and density of defect centers in comparison with
microcrystalline samples prepared by sintering at high temperature.
The mechanism is based on reduction of Sm(3+) to Sm(2+) by trapping
electrons that are created upon exposure to ionizing radiation in the
BaFCl host. The (5)D-(7)F f-f luminescence lines can be very
efficiently excited via the parity allowed 4f(6)→4f(5)5d transition at
~417 nm. The latter wavelength is ideal for efficient excitation by
blue-violet laser diodes as the transition is electric dipole allowed
and thus relatively intense (400 L/(mol⋅cm)).
The phosphor has potential applications in personal dosimetry,
dosimetry and imaging in radiotherapy, and medical imaging.
Non-commercial and potential uses
===================================
* The change in electrical resistivity in samarium monochalcogenides
can be used in a pressure sensor or in a memory device triggered
between a low-resistance and high-resistance state by external
pressure, and such devices are being developed commercially. Samarium
monosulfide also generates electric voltage upon moderate heating to
about 150 C that can be applied in thermoelectric power converters.
* Analysis of relative concentrations of samarium and neodymium
isotopes (147)Sm, (144)Nd, and (143)Nd allows determination of the age
and origin of rocks and meteorites in samarium-neodymium dating. Both
elements are lanthanides and are very similar physically and
chemically. Thus, Sm-Nd dating is either insensitive to partitioning
of the marker elements during various geologic processes, or such
partitioning can well be understood and modeled from the ionic radii
of said elements.
* The Sm(3+) ion is a potential activator for use in warm-white light
emitting diodes. It offers high luminous efficacy due to narrow
emission bands; but the generally low quantum efficiency and too
little absorption in the UV-A to blue spectral region hinders
commercial application.
* Samarium is used for ionosphere testing. A rocket spreads samarium
monoxide as a red vapor at high altitude, and researchers test how the
atmosphere disperses it and how it impacts radio transmissions.
* Samarium hexaboride, , has recently been shown to be a topological
insulator with potential uses in quantum computing.
Biological role and precautions
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Samarium salts stimulate metabolism, but it is unclear whether this is
from samarium or other lanthanides present with it. The total amount
of samarium in adults is about 50 μg, mostly in liver and kidneys and
with ~8 μg/L being dissolved in blood. Samarium is not absorbed by
plants to a measurable concentration and so is normally not part of
human diet. However, a few plants and vegetables may contain up to 1
part per million of samarium. Insoluble salts of samarium are
non-toxic and the soluble ones are only slightly toxic. When ingested,
only 0.05% of samarium salts are absorbed into the bloodstream and the
remainder are excreted. From the blood, 45% goes to the liver and 45%
is deposited on the surface of the bones where it remains for 10
years; the remaining 10% is excreted.
External links
======================================================================
*[
https://education.jlab.org/itselemental/ele062.html It's Elemental -
Samarium]
*[
https://www.organic-chemistry.org/chemicals/reductions/samariumlowvalent.shtm
Reducing Agents > Samarium low valent]
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/Samarium
