Samarium

Template:Use American English Template:Infobox samarium 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 Template:Convert, 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 the reactor operation and is one of the important factors considered in the 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.<ref name=emsley />

Physical properties

Samarium is a rare earth element with a hardness and density similar to zinc. With a boiling point of Template:Convert, 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.<ref name="Lange">Template:Cite book</ref><ref name="CRC" /> 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.<ref>Template:Cite journal</ref>

In ambient conditions, samarium has a rhombohedral structure (α form). Upon heating to Template:Convert, its crystal symmetry changes to hexagonal close-packed (hcp),; it has actual transition temperature depending on metal purity. Further heating to Template:Convert transforms the metal into a body-centered cubic (bcc) phase. Heating to Template:Convert 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.<ref name="sm" /> In one study, the dhcp phase could be produced without compression, using a nonequilibrium annealing regime with a rapid temperature change between about Template:Convert and Template:Convert, 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.<ref name="sm">Template:Cite journal</ref>

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.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Individual samarium atoms can be isolated by encapsulating them into fullerene molecules.<ref>Template:Cite journal</ref> 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.<ref>Template:Cite journal</ref> 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.<ref name="Wu2008">Template:Cite journal</ref>

Chemical properties

In air, samarium slowly oxidizes at room temperature and spontaneously ignites at Template:Convert.<ref name="emsley" /><ref name="CRC" /> 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:<ref name="we" />

Template:Chem2

Samarium dissolves readily in dilute sulfuric acid to form solutions containing the yellow<ref name="g1243">Greenwood, p. 1243</ref> to pale green Sm(III) ions, which exist as Template:Chem2 complexes:<ref name="we">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Template:Chem2

Samarium is one of the few lanthanides with a relatively accessible +2 oxidation state, alongside Eu and Yb.<ref>Template:Cite book</ref> Template:Chem2 ions are blood-red in aqueous solution.<ref name="g1248">Greenwood, p. 1248</ref>

Compounds

Formula	color	symmetry	space group	No	Pearson symbol	a (pm)	b (pm)	c (pm)	Z	density, g/cm3
Sm	silvery	trigonal<ref name="sm"/>	RTemplate:Overlinem	166	hR9	362.9	362.9	2621.3	9	7.52
Sm	silvery	hexagonal<ref name="sm" />	P63/mmc	194	hP4	362	362	1168	4	7.54
Sm	silvery	tetragonal<ref name="sm2">Template:Cite journal</ref>	I4/mmm	139	tI2	240.2	240.2	423.1	2	20.46
SmO	golden	cubic<ref name="smox">Template:Cite journal</ref>	FmTemplate:Overlinem	225	cF8	494.3	494.3	494.3	4	9.15
Sm2O3		trigonal<ref name="smo">Template:Cite journal</ref>	PTemplate:Overlinem1	164	hP5	377.8	377.8	594	1	7.89
Sm2O3		monoclinic<ref name="smo" />	C2/m	12	mS30	1418	362.4	885.5	6	7.76
Sm2O3		cubic<ref name="smo2">Template:Cite journal</ref>	IaTemplate:Overline	206	cI80	1093	1093	1093	16	7.1
SmH2		cubic<ref name="smh2">Template:Cite journal</ref>	FmTemplate:Overlinem	225	cF12	537.73	537.73	537.73	4	6.51
SmH3		hexagonal<ref name="smh3">Template:Cite journal</ref>	PTemplate:Overlinec1	165	hP24	377.1	377.1	667.2	6
Sm2B5	gray	monoclinic<ref>Template:Cite journal</ref>	P21/c	14	mP28	717.9	718	720.5	4	6.49
SmB2		hexagonal<ref name="smb2">Template:Cite journal</ref>	P6/mmm	191	hP3	331	331	401.9	1	7.49
SmB4		tetragonal<ref>Template:Cite journal</ref>	P4/mbm	127	tP20	717.9	717.9	406.7	4	6.14
SmB6		cubic<ref name="smb6">Template:Cite journal</ref>	PmTemplate:Overlinem	221	cP7	413.4	413.4	413.4	1	5.06
SmB66		cubic<ref>Template:Cite journal</ref>	FmTemplate:Overlinec	226	cF1936	2348.7	2348.7	2348.7	24	2.66
Sm2C3		cubic<ref name="smc" />	ITemplate:Overline3d	220	cI40	839.89	839.89	839.89	8	7.55
SmC2		tetragonal<ref name="smc">Template:Cite journal</ref>	I4/mmm	139	tI6	377	377	633.1	2	6.44
SmF2	purple<ref name="g1241" />	cubic<ref name="smf2">Template:Cite journal</ref>	FmTemplate:Overlinem	225	cF12	587.1	587.1	587.1	4	6.18
SmF3	white<ref name="g1241" />	orthorhombic<ref name="smf2" />	Pnma	62	oP16	667.22	705.85	440.43	4	6.64
SmCl2	brown<ref name="g1241" />	orthorhombic<ref name="smcl2">Template:Cite journal</ref>	Pnma	62	oP12	756.28	450.77	901.09	4	4.79
SmCl3	yellow<ref name="g1241" />	hexagonal<ref name="smf2" />	P63/m	176	hP8	737.33	737.33	416.84	2	4.35
SmBr2	brown<ref name="g1241" />	orthorhombic<ref name="smbr2">Template:Cite journal</ref>	Pnma	62	oP12	797.7	475.4	950.6	4	5.72
SmBr3	yellow<ref name="g1241" />	orthorhombic<ref name="smbr3">Template:Cite journal</ref>	Cmcm	63	oS16	404	1265	908	2	5.58
SmI2	green<ref name="g1241">Greenwood, p. 1241</ref>	monoclinic	P21/c	14	mP12
SmI3	orange<ref name="g1241" />	trigonal<ref name="smI3">Template:Cite journal</ref>	RTemplate:Overline	63	hR24	749	749	2080	6	5.24
SmN		cubic<ref name="smn">Template:Cite journal</ref>	FmTemplate:Overlinem	225	cF8	357	357	357	4	8.48
SmP		cubic<ref name="smp">Template:Cite journal</ref>	FmTemplate:Overlinem	225	cF8	576	576	576	4	6.3
SmAs		cubic<ref name="smas">Template:Cite journal</ref>	FmTemplate:Overlinem	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 Template:Convert converts it to the more stable monoclinic phase.<ref name="smo" /> Cubic Sm₂O₃ has also been described.<ref name="smo2" />

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.<ref name="smox" /><ref name="g1239">Greenwood, p. 1239</ref>

Chalcogenides

Template:See also 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.<ref>Template:Cite journal</ref> 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.<ref name="b1">Template:Cite book</ref> 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.<ref name="emsley" /><ref>Template:Cite journal</ref>

Halides

File:Samarium(III) chloride hexahydrate.jpg

Samarium trichloride

Samarium metal reacts with all the halogens, forming trihalides:<ref name="g1236">Greenwood, pp. 1236, 1241</ref>

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.<ref name="smcl2" /> The diiodide can also be prepared by heating SmI₃, or by reacting the metal with 1,2-diiodoethane in anhydrous tetrahydrofuran at room temperature:<ref name="g1240">Greenwood, p. 1240</ref>

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,<ref name="smf2" /> Sm₁₁Br₂₄, Sm₅Br₁₁ and Sm₆Br₁₃.<ref>Template:Cite journal</ref>

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),<ref>Template:Cite journal</ref> and similar treatment results in a new phase of samarium triiodide (density 5.97 g/cm³).<ref>Template:Cite journal</ref>

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.<ref name="smb6b" /> 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.<ref name="smb6" /> 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.<ref name="smb2" />

Samarium hexaboride

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}}

Samarium hexaboride is a typical intermediate-valence compound where samarium is present both as Sm²⁺ and Sm³⁺ ions in a 3:7 ratio.<ref name="smb6b">Template:Cite journal</ref> 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.<ref>Template:Cite journal</ref> 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.<ref>Template:Cite journal</ref>

Other inorganic compounds

File:Samarium-sulfate.jpg

Samarium sulfate, Sm₂(SO₄)₃

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.<ref name="smc" /> 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 Template:Convert 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.<ref name="smp" /> A similar procedure is adopted for the monarsenide SmAs, but the synthesis temperature is higher at Template:Convert.<ref name="smas" />

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 Sm_aX_b, where the b/a ratio varies between 0.5 and 3.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Organometallic compounds

Samarium forms a cyclopentadienide Template:Chem2 and its chloroderivatives Template:Chem2 and Template:Chem2. They are prepared by reacting samarium trichloride with Template:Chem2 in tetrahydrofuran. Contrary to cyclopentadienides of most other lanthanides, in Template:Chem2 some Template:Chem2 rings bridge each other by forming ring vertexes η¹ or edges η² toward another neighboring samarium, thus creating polymeric chains.<ref name="g1248" /> The chloroderivative Template:Chem2 has a dimer structure, which is more accurately expressed as Template:Chem2. There, the chlorine bridges can be replaced, for instance, by iodine, hydrogen or nitrogen atoms or by CN groups.<ref name="g1249">Greenwood, p. 1249</ref>

The (Template:Chem2)⁻ ion in samarium cyclopentadienides can be replaced by the indenide (Template:Chem2)⁻ or cyclooctatetraenide (Template:Chem2)²⁻ ring, resulting in Template:Chem2 or Template:Chem2. The latter compound has a structure similar to uranocene. There is also a cyclopentadienide of divalent samarium, Template:Chem2 a solid that sublimates at about Template:Convert. Contrary to ferrocene, the Template:Chem2 rings in Template:Chem2 are not parallel but are tilted by 40°.<ref name="g1249" /><ref>Template:Cite journal</ref>

A metathesis reaction in tetrahydrofuran or ether gives alkyls and aryls of samarium:<ref name="g1249" />

Template:Chem2

Template:Chem2

Here R is a hydrocarbon group and Me = methyl.

Isotopes

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} 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 = 1.06Template:E years) and ¹⁴⁸Sm (7Template:E years), with ¹⁵²Sm being the most abundant (26.75%).Template:NUBASE2020 ¹⁴⁹Sm is listed by various sources as being stable,Template:NUBASE2020<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> but some sources state that it is radioactive,<ref>Holden, Norman E. "Table of the isotopes" in Template:RubberBible86th</ref> with a lower bound for its half-life given as Template:Val years.Template:NUBASE2020 Some observationally stable samarium isotopes are predicted to decay to isotopes of neodymium.<ref name="rare_decays">Template:Cite journal</ref> 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.Template:NUBASE2020 The known isotopes range from ¹²⁹Sm to ¹⁶⁸Sm.Template:NUBASE2020<ref name=Ln922>Template:Cite journal</ref> 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).Template:NUBASE2020 Natural samarium has a radioactivity of 127 Bq/g, mostly due to ¹⁴⁷Sm,<ref name=iaea1512>Template:Cite report</ref> which alpha decays to ¹⁴³Nd with a half-life of 1.06Template:E years and is used in samarium–neodymium dating.<ref name=DePaolo147Sm>Template:Cite journal</ref><ref name=McCulloch147Sm>Template:Cite journal</ref> ¹⁴⁶Sm is an extinct radionuclide, with the half-life of 9.20Template:E years.<ref name=Chiera2024/> 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.<ref>Template:Cite journal</ref> It can be used in radiometric dating.<ref>Template:Cite journal</ref>

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.<ref>Template:Cite book</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Its neutron cross section is 41000 barns for thermal neutrons.<ref>Template:Cite conference</ref> 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.<ref>DOE Handbook, pp. 43–47.</ref>

File:153Sm-lexidronam structure.svg

Chemical structure of Sm-EDTMP

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.<ref name="emsley" /> The corresponding drug has several names including samarium (¹⁵³Sm) lexidronam; its trade name is Quadramet.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

History

File:Lecoq de Boisbaudran.jpg

Paul Émile Lecoq de Boisbaudran, the discoverer of samarium

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.<ref>Greenwood, p. 1229</ref><ref name="brit">Samarium, Encyclopædia Britannica on-line</ref> Boisbaudran isolated samarium oxide and/or hydroxide in Paris in 1879 from the mineral samarskite Template:Chem2) and identified a new element in it via sharp optical absorption lines.<ref name="CRC">Template:Cite book</ref> Swiss chemist Marc Delafontaine announced a new element decipium (from Template:Langx meaning "deceptive, misleading") in 1878,<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> but later in 1880–1881 demonstrated that it was a mix of several elements, one being identical to Boisbaudran's samarium.<ref name="iupac">Template:CIAAW2003</ref><ref>Template:Cite journal</ref> 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,<ref name="van" /><ref name="Weeks">Template:Cite book</ref><ref name="XIII">Template:Cite journal</ref> 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.<ref name="bse">Samarskite, Great Soviet Encyclopedia (in Russian)</ref><ref>Template:Cite journal</ref><ref>Shipley, Joseph Twadell. The Origins of English Words: A Discursive Dictionary of Indo-European Roots, JHU Press, 2001, p.90. Template:ISBN</ref> Samarium was thus the first chemical element to be named after a person.<ref name="van" /><ref name="RSC" /> 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.<ref name="van">Samarium: History & Etymology. Elements.vanderkrogt.net. Retrieved on 2013-03-21.</ref><ref>Template:Cite journal</ref>

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.<ref>Template:Cite journal</ref> Nowadays, a similar commodity product has the name "samarium-europium-gadolinium" (SEG) concentrate.<ref name="RSC">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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 1Template:Endash2% 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. Template:As of, being in oversupply, samarium oxide is cheaper on a commercial scale than its relative abundance in the ore might suggest.<ref name="price" />

Occurrence and production

File:Samarskite-fresh.jpg

Samarskite

Samarium concentration in soils varies between 2 and 23 ppm, and oceans contain about 0.5–0.8 parts per trillion.<ref name="emsley" /> The median value for its abundance in the Earth's crust used by the CRC Handbook is 7 parts per million (ppm)<ref name=CRCabundance>ABUNDANCE OF ELEMENTS IN THE EARTH’S CRUST AND IN THE SEA, CRC Handbook of Chemistry and Physics, 97th edition (2016–2017), p. 14-17</ref> and is the 40th most abundant element.<ref>Template:Cite book</ref> 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.<ref name="LA2" />

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%)<ref name="CRC" /> 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.<ref name="emsley" /> 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)<ref name="LA2" /> and India (2,700 tonnes).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Samarium is usually sold as oxide, which at the price of about US$30/kg is one of the cheapest lanthanide oxides.<ref name="price">What are their prices?, Lynas corp.</ref> 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 1794 °C) and lanthanum (b.p. 3464 °C).<ref name="brit" />

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.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It is also made by neutron capture by samarium-149, which is added to the control rods of nuclear reactors. Therefore, ¹⁵¹Sm is present in spent nuclear fuel and radioactive waste.<ref name="LA2" />

Applications

File:Samariumiodide.jpg

Barbier reaction using Template:Chem2

Magnets

An important use of samarium is samarium–cobalt magnets, which are nominally Template:Chem2 or Template:Chem2.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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 Template:Convert (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.<ref name="emsley" /> 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.

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.<ref name="CRC" /> Samarium(III) triflate Template:Chem2, that is Template:Chem2, is one of the most efficient Lewis acid catalysts for a halogen-promoted Friedel–Crafts reaction with alkenes.<ref>Template:Cite journal</ref> 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.<ref>Template:Cite book</ref>

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.<ref name="emsley" /><ref name="CRC" />

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 ¹⁴⁹Sm 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 ¹⁵⁰Sm, ¹⁵²Sm, and ¹⁵³Sm, and 6,800 barns for natural (mixed-isotope) samarium.<ref name="CRC" /><ref name="LA2" /><ref>Thermal neutron capture cross sections and resonance integrals – Fission product nuclear data. ipen.br</ref>

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.<ref>Bud, Robert and Gummett, Philip Cold War, Hot Science: Applied Research in Britain's Defence Laboratories, 1945–1990, NMSI Trading Ltd, 2002 Template:ISBN p. 268</ref><ref>Template:Cite journal</ref> 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).<ref>Template:Cite journal</ref>

Storage phosphor

In 2007 it was shown that nanocrystalline BaFCl:Sm³⁺ as prepared by co-precipitation can serve as a very efficient X-ray storage phosphor.<ref>Template:Cite journal</ref> 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.<ref>Template:Cite journal</ref> The mechanism is based on reduction of Sm³⁺ to Sm²⁺ by trapping electrons that are created upon exposure to ionizing radiation in the BaFCl host. The ⁵D_J–⁷F_J f–f luminescence lines can be very efficiently excited via the parity allowed 4f⁶→4f⁵5d 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)).<ref>Template:Cite journal</ref> The phosphor has potential applications in personal dosimetry, dosimetry and imaging in radiotherapy, and medical imaging.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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,<ref>Template:Cite patent</ref> and such devices are being developed commercially.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref> Samarium monosulfide also generates electric voltage upon moderate heating to about Template:Convert that can be applied in thermoelectric power converters.<ref>Template:Cite journal</ref>

• Analysis of relative concentrations of samarium and neodymium isotopes ¹⁴⁷Sm, ¹⁴⁴Nd, and ¹⁴³Nd 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.<ref>Bowen, Robert and Attendorn, H -G Isotopes in the Earth Sciences, Springer, 1988, Template:ISBN, pp. 270 ff</ref>
• The Sm³⁺ 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.<ref>Template:Cite journal</ref>
• 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.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

• Samarium hexaboride, Template:Chem2, has recently been shown to be a topological insulator with potential uses in quantum computing.<ref name="physorgsamarium">Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Biological role and precautions

Template:Chembox 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.<ref name="emsley">Template:Cite book</ref><ref name="Bayouth">Template:Cite journal</ref> 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.<ref name="LA2">Human Health Fact Sheet on Samarium Template:Webarchive, Los Alamos National Laboratory</ref>

Bibliography

• Template:Cite book

External links

• It's Elemental – Samarium
• Reducing Agents > Samarium low valent