Samarium

Samarium is a chemical element with 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 assumes 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. The last compound is a common reducing agent in chemical synthesis. Samarium has no significant biological role but is only slightly toxic.

Samarium was discovered in 1879 by the French chemist Paul-Émile Lecoq de Boisbaudran and named after the mineral samarskite from which it was isolated. The mineral itself was earlier named after a Russian mine official, Colonel Vassili Samarsky-Bykhovets, who thereby became the first person to have a chemical element named after him, albeit indirectly. Although classified as a rare-earth element, samarium is the 40th most abundant element in the Earth's crust and is more common than metals such as tin. Samarium occurs with 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 major commercial application 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 (1,292 °F), without losing their magnetic properties, due to the alloy's higher Curie point. The radioactive isotope samarium-153 is the active component of the drug samarium (153Sm) lexidronam (Quadramet), which kills cancer cells in the treatment of lung cancer, prostate cancer, breast cancer and osteosarcoma. Another isotope, samarium-149, is a strong neutron absorber and is therefore added to the control rods of nuclear reactors. It is also formed as a decay product during the reactor operation and is one of the important factors considered in the reactor design and operation. Other applications of samarium include catalysis of chemical reactions, radioactive dating and X-ray lasers.

Samarium,  62Sm
Samarium-2
Samarium
Pronunciation/səˈmɛəriəm/ (sə-MAIR-ee-əm)
Appearancesilvery white
Standard atomic weight Ar, std(Sm)150.36(2)[1]
Samarium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Sm

Pu
promethiumsamariumeuropium
Atomic number (Z)62
Groupgroup n/a
Periodperiod 6
Blockf-block
Element category  lanthanide
Electron configuration[Xe] 4f6 6s2
Electrons per shell
2, 8, 18, 24, 8, 2
Physical properties
Phase at STPsolid
Melting point1345 K ​(1072 °C, ​1962 °F)
Boiling point2173 K ​(1900 °C, ​3452 °F)
Density (near r.t.)7.52 g/cm3
when liquid (at m.p.)7.16 g/cm3
Heat of fusion8.62 kJ/mol
Heat of vaporization192 kJ/mol
Molar heat capacity29.54 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1001 1106 1240 (1421) (1675) (2061)
Atomic properties
Oxidation states+1, +2, +3, +4 (a mildly basic oxide)
ElectronegativityPauling scale: 1.17
Ionization energies
  • 1st: 544.5 kJ/mol
  • 2nd: 1070 kJ/mol
  • 3rd: 2260 kJ/mol
Atomic radiusempirical: 180 pm
Covalent radius198±8 pm
Color lines in a spectral range
Spectral lines of samarium
Other properties
Natural occurrenceprimordial
Crystal structurerhombohedral
Rhombohedral crystal structure for samarium
Speed of sound thin rod2130 m/s (at 20 °C)
Thermal expansion(r.t.) (α, poly) 12.7 µm/(m·K)
Thermal conductivity13.3 W/(m·K)
Electrical resistivity(r.t.) (α, poly) 0.940 µΩ·m
Magnetic orderingparamagnetic[2]
Magnetic susceptibility+1860.0·10−6 cm3/mol (291 K)[3]
Young's modulusα form: 49.7 GPa
Shear modulusα form: 19.5 GPa
Bulk modulusα form: 37.8 GPa
Poisson ratioα form: 0.274
Vickers hardness410–440 MPa
Brinell hardness440–600 MPa
CAS Number7440-19-9
History
Namingafter the mineral samarskite (itself named after Vassili Samarsky-Bykhovets)
Discovery and first isolationLecoq de Boisbaudran (1879)
Main isotopes of samarium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
144Sm 3.08% stable
145Sm syn 340 d ε 145Pm
146Sm syn 6.8×107 y α 142Nd
147Sm 15.00% 1.06×1011 y α 143Nd
148Sm 11.25% 7×1015 y α 144Nd
149Sm 13.82% stable
150Sm 7.37% stable
151Sm syn 90 y β 151Eu
152Sm 26.74% stable
153Sm syn 46.284 h β 153Eu
154Sm 22.74% stable

Physical properties

Samarium is a rare earth metal having a hardness and density similar to those of zinc. With the boiling point of 1794 °C, samarium is the third most volatile lanthanide after ytterbium and europium; this property facilitates separation of samarium from the mineral ore. At ambient conditions, samarium normally assumes a rhombohedral structure (α form). Upon heating to 731 °C, its crystal symmetry changes into hexagonally close-packed (hcp), however the transition temperature depends on the metal purity. Further heating to 922 °C transforms the metal into a body-centered cubic (bcc) phase. Heating to 300 °C combined with compression to 40 kbar results in a double-hexagonally close-packed structure (dhcp). Applying 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.[4] In one study, the dhcp phase could be produced without compression, using a nonequilibrium annealing regime with a rapid temperature change between about 400 and 700 °C, confirming the transient character of this samarium phase. Also, thin films of samarium obtained by vapor deposition may contain the hcp or dhcp phases at ambient conditions.[4]

Samarium (and its sesquioxide) are paramagnetic at room temperature. Their corresponding effective magnetic moments, below 2µB, are the 3rd lowest among the lanthanides (and their oxides) after lanthanum and lutetium. The metal transforms to an antiferromagnetic state upon cooling to 14.8 K.[5][6] Individual samarium atoms can be isolated by encapsulating them into fullerene molecules.[7] They can also be doped between the C60 molecules in the fullerene solid, rendering it superconductive at temperatures below 8 K.[8] Samarium doping of iron-based superconductors – the most recent class of high-temperature superconductors – allows enhancing their transition temperature to 56 K, which is the highest value achieved so far in this series.[9]

Chemical properties

Freshly prepared samarium has a silvery luster. In air, it slowly oxidizes at room temperature and spontaneously ignites at 150 °C.[10][11] 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 quite quickly with hot water to form samarium hydroxide:[12]

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

Samarium dissolves readily in dilute sulfuric acid to form solutions containing the yellow[13] to pale green Sm(III) ions, which exist as [Sm(OH2)9]3+ complexes:[12]

2 Sm (s) + 3 H2SO4 (aq) → 2 Sm3+ (aq) + 3 SO2−
4
(aq) + 3 H2 (g)

Samarium is one of the few lanthanides that exhibit the oxidation state +2. The Sm2+ ions are blood-red in aqueous solution.[14]

Compounds

Oxides

The most stable oxide of samarium is the sesquioxide Sm2O3. As many other 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 rather high (2345 °C) and therefore melting is usually achieved not by direct heating, but with induction heating, through a radio-frequency coil. The Sm2O3 crystals of monoclinic symmetry can be grown by the flame fusion method (Verneuil process) from the 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.[17] Cubic Sm2O3 has also been described.[18]

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 elevated temperature (1000 °C) and pressure above 50 kbar; lowering the pressure resulted in an incomplete reaction. SmO has the cubic rock-salt lattice structure.[16][36]

Chalcogenides

Samarium forms trivalent sulfide, selenide and telluride. Divalent chalcogenides SmS, SmSe and SmTe with cubic rock-salt crystal structure are also known. They are remarkable by converting from 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 spectacular color change in SmS from black to golden yellow when its crystals of films are scratched or polished. The transition does not change lattice symmetry, but there is a sharp decrease (~15%) in the crystal volume.[37] It shows hysteresis, that is when the pressure is released, SmS returns to the semiconducting state at much lower pressure of about 0.4 kbar.[10][38]

Halides

Samarium metal reacts with all the halogens, forming trihalides:[39]

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 dihalides.[29] The diiodide can also be prepared by heating SmI3, or by reacting the metal with 1,2-diiodoethane in anhydrous tetrahydrofuran at room temperature:[40]

Sm (s) + ICH2-CH2I → SmI2 + CH2=CH2.

In addition to dihalides, the reduction also produces numerous non-stoichiometric samarium halides with a well-defined crystal structure, such as Sm3F7, Sm14F33, Sm27F64,[28] Sm11Br24, Sm5Br11 and Sm6Br13.[41]

As reflected in the table above, samarium halides change their crystal structures when one type of halide atoms 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),[42] and similar treatment results in a new phase of samarium triiodide (density 5.97 g/cm3).[43]

Borides

Sintering powders of samarium oxide and boron, in vacuum, yields a powder containing several samarium boride phases, and their volume ratio can be controlled through the mixing proportion.[44] The powder can be converted into larger crystals of a certain samarium boride 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.[24] 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 formations of SmB6.[22]

Samarium hexaboride

Samarium hexaboride is a typical intermediate-valence compound where samarium is present both as Sm2+ and Sm3+ ions at the ratio 3:7.[44] It belongs to a class of Kondo insulators, that is at high temperatures (above 50 K), its properties are typical of a Kondo metal, with metallic electrical conductivity characterized by strong electron scattering, whereas at low temperatures, it behaves as a non-magnetic insulator with a narrow band gap of about 4–14 meV.[45] 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 reduced the rate of electron-phonon scattering.[46]

New research seems to show that it may be a topological insulator.[47][48][49]

Other inorganic compounds

Samarium-sulfate
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 are studied also under inert atmosphere.[26] Samarium monophosphide SmP is a semiconductor with the bandgap of 1.10 eV, the same as in silicon, and high 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.[34] Similar procedure is adopted for the monarsenide SmAs, but the synthesis temperature is higher at 1800 °C.[35]

Numerous crystalline binary compounds are known for samarium and one of the group-14, 15 or 16 element 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.[50][51][52]

Organometallic compounds

Samarium forms a cyclopentadienide Sm(C5H5)3 and its chloroderivatives Sm(C5H5)2Cl and Sm(C5H5)Cl2. They are prepared by reacting samarium trichloride with NaC5H5 in tetrahydrofuran. Contrary to cyclopentadienides of most other lanthanides, in Sm(C5H5)3 some C5H5 rings bridge each other by forming ring vertexes η1 or edges η2 toward another neighboring samarium atom, thereby creating polymeric chains.[14] The chloroderivative Sm(C5H5)2Cl has a dimer structure, which is more accurately expressed as (η5-C5H5)2Sm(µ-Cl)25-C5H5)2. There, the chlorine bridges can be replaced, for instance, by iodine, hydrogen or nitrogen atoms or by CN groups.[53]

The (C5H5) ion in samarium cyclopentadienides can be replaced by the indenide (C9H7) or cyclooctatetraenide (C8H8)2− ring, resulting in Sm(C9H7)3 or KSm(η8-C8H8)2. The latter compound has a similar structure to that of uranocene. There is also a cyclopentadienide of divalent samarium, Sm(C5H5)2 – a solid that sublimates at about 85 °C. Contrary to ferrocene, the C5H5 rings in Sm(C5H5)2 are not parallel but are tilted by 40°.[53][54]

Alkyls and aryls of samarium are obtained through a metathesis reaction in tetrahydrofuran or ether:[53]

SmCl3 + 3 LiR → SmR3 + 3 LiCl
Sm(OR)3 + 3 LiCH(SiMe3)2 → Sm{CH(SiMe3)2}3 + 3 LiOR

Here R is a hydrocarbon group and Me stands for methyl.

Isotopes

Naturally occurring samarium has a radioactivity of 128 Bq/g. It is composed of four stable isotopes: 144Sm, 150Sm, 152Sm and 154Sm, and three extremely long-lived radioisotopes, 147Sm (half-life t1/2 = 1.06×1011 years), 148Sm (7×1015 years) and 149Sm (>2×1015 years), with 152Sm being the most abundant (natural abundance 26.75%).[55] 149Sm is listed by various sources either as stable[55][56] or radioactive isotope.[57]

The long-lived isotopes,146Sm, 147Sm, and 148Sm, primarily decay by emission of alpha particles to isotopes of neodymium. Lighter unstable isotopes of samarium primarily decay by electron capture to isotopes of promethium, while heavier ones convert through beta decay to isotopes of europium.[55]

The alpha decay of 147Sm to 143Nd with a half-life of 1.06×1011 years serve for samarium–neodymium dating.

The half-lives of 151Sm and 145Sm are 90 years and 340 days, respectively. All the remaining radioisotopes have half-lives that are less than 2 days, and the majority of these have half-lives that are less than 48 seconds. Samarium also has five nuclear isomers with the most stable being 141mSm (half-life 22.6 minutes), 143m1Sm (t1/2 = 66 seconds) and 139mSm (t1/2 = 10.7 seconds).[55]

History

Lecoq de Boisbaudran
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 the priority to the French chemist Paul Émile Lecoq de Boisbaudran.[58][59] Boisbaudran isolated samarium oxide and/or hydroxide in Paris in 1879 from the mineral samarskite ((Y,Ce,U,Fe)3(Nb,Ta,Ti)5O16) and identified a new element in it via sharp optical absorption lines.[11] The Swiss chemist Marc Delafontaine announced a new element decipium (from Latin: decipiens meaning "deceptive, misleading") in 1878,[60][61] but later in 1880–1881 demonstrated that it was a mixture of several elements, one being identical to the Boisbaudran's samarium.[62][63] Although samarskite was first found in the remote Russian region of Urals, by the late 1870s its deposits had been located in other places making the mineral available to many researchers. In particular, it was found that the samarium isolated by Boisbaudran was also impure and contained comparable amount of europium. The pure element was produced only in 1901 by Eugène-Anatole Demarçay.[64]

Boisbaudran named his element samaria 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 Rose and Heinrich Rose, to study the mineral samples from the Urals.[65][66][67] In this sense samarium was the first chemical element to be named after a person.[64][68] Later the name samaria used by Boisbaudran was transformed into samarium, to conform with other element names, and samaria nowadays is sometimes used to refer to samarium oxide, by analogy with yttria, zirconia, alumina, ceria, holmia, etc. The symbol Sm was suggested for samarium; however an alternative Sa was frequently used instead until the 1920s.[64][69]

Prior to the advent of ion-exchange separation technology in the 1950s, samarium had no commercial uses in pure form. However, a by-product of the fractional crystallization purification of neodymium was a mixture of samarium and gadolinium that acquired the name of "Lindsay Mix" after the company that made it. This material is thought to have been used for nuclear control rods in some early nuclear reactors. Nowadays, a similar commodity product has the name "samarium-europium-gadolinium" (SEG) concentrate.[68] It is prepared by solvent extraction from the mixed lanthanides isolated from bastnäsite (or monazite). Since the heavier lanthanides have the greater 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 onward with the separation of the components of SEG, which typically makes up only one or two percent of the original ore. Such producers will therefore be making SEG with a view to marketing it to the specialized processors. In this manner, the valuable europium content of the ore is rescued for use in phosphor manufacture. Samarium purification follows the removal of the europium. As of 2012, being in oversupply, samarium oxide is less expensive on a commercial scale than its relative abundance in the ore might suggest.[70]

Occurrence and production

Samarskite-fresh
Samarskite

With the average concentration of about 8 parts per million (ppm), samarium is the 40th most abundant element in the Earth's crust. It is the fifth most abundant lanthanide and is more common than elements such as tin. Samarium concentration in soils varies between 2 and 23 ppm, and oceans contain about 0.5–0.8 parts per trillion.[10] 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.[71]

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%)[11] 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.[10] 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)[71] and India (2,700 tonnes).[72] Samarium is usually sold as oxide, which at the price of about 30 USD/kg is one of the cheapest lanthanide oxides.[70] 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).[59]

Domination of samarium in minerals is unique. Minerals with essential (dominant) samarium include monazite-(Sm) and florencite-(Sm). They are very rare.[73][74][75][76]

Samarium-151 is produced in nuclear fission of uranium with the yield of about 0.4% of the total number of fission events. It is also synthesized upon neutron capture by samarium-149, which is added to the control rods of nuclear reactors. Consequently, samarium-151 is present in spent nuclear fuel and radioactive waste.[71]

Applications

Samariumiodide
Barbier reaction using SmI2

One of the most important applications of samarium is in samarium–cobalt magnets, which have a nominal composition of SmCo5 or Sm2Co17. They have high permanent magnetization, which is about 10,000 times that of iron and is second only to that of neodymium magnets. However, samarium-based magnets have higher resistance to demagnetization, as 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.[10] 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.

Another important application of samarium and its compounds is as catalyst and chemical reagent. Samarium catalysts assist decomposition of plastics, dechlorination of pollutants such as polychlorinated biphenyls (PCBs), as well as the dehydration and dehydrogenation of ethanol.[11] Samarium(III) triflate (Sm(OTf)3, that is Sm(CF3SO3)3), is one of the most efficient Lewis acid catalysts for a halogen-promoted Friedel–Crafts reaction with alkenes.[77] Samarium(II) iodide is a very common reducing and coupling agent in organic synthesis, for example in the desulfonylation reactions; annulation; Danishefsky, Kuwajima, Mukaiyama and Holton Taxol total syntheses; strychnine total synthesis; Barbier reaction and other reductions with samarium(II) iodide.[78]

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 "flint" ignition device of many lighters and torches.[10][11]

153Sm-lexidronam structure
Chemical structure of Sm-EDTMP

Radioactive samarium-153 is a beta emitter with a half-life of 46.3 hours. It is used to kill cancer cells in the treatment of 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.[10] The corresponding drug has several names including samarium (153Sm) lexidronam; its trade name is Quadramet.[79][80][81]

Samarium-149 has high cross-section for neutron capture (41,000 barns) and is therefore used in the control rods of nuclear reactors. Its advantage compared to competing materials, such as boron and cadmium, is stability of absorption – most of the fusion and decay products of samarium-149 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 is 6,800 barns for natural (mixed-isotope) samarium.[11][71][82] Among the decay products in a nuclear reactor, samarium-149 is regarded as the second most important for the reactor design and operation after xenon-135.[83]

Samarium hexaboride, abbreviated SmB6, has recently been shown to be a topological insulator with potential applications to quantum computing.[84]

Non-commercial and potential applications

Samarium-doped calcium fluoride crystals were used as an active medium in one of the first solid-state lasers designed and constructed by Peter Sorokin (co-inventor of the dye laser) and Mirek Stevenson at IBM research labs in early 1961. This samarium laser emitted pulses of red light at 708.5 nm. It had to be cooled by liquid helium and thus did not find practical applications.[85][86]

Another samarium-based laser became the first saturated X-ray laser operating at wavelengths shorter than 10 nanometers. It provided 50-picosecond pulses at 7.3 and 6.8 nm suitable for applications 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).[87]

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,[88] and such devices are being developed commercially.[89] Samarium monosulfide also generates electric voltage upon moderate heating to about 150 °C that can be applied in thermoelectric power converters.[90]

The analysis of relative concentrations of samarium and neodymium isotopes 147Sm, 144Nd, and 143Nd allows the determination of the age and origin of rocks and meteorites in samarium–neodymium dating. Both elements are lanthanides and have very similar physical and chemical properties. Therefore, Sm–Nd dating is either insensitive to partitioning of the marker elements during various geological processes, or such partitioning can well be understood and modeled from the ionic radii of the involved elements.[91]

The Sm3+ ion is a potential activator for use in warm-white light emitting diodes. It offers high luminous efficacy due to the narrow emission bands, however, the generally low quantum efficiency and insufficient absorption in the UV-A to blue spectral region hinders commercial application.[92]

In recent years it has been demonstrated that nanocrystalline BaFCl:Sm3+ as prepared by a co-precipitation can serve as a very efficient x-ray storage phosphor.[93] 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 an astounding ∼500,000 times because of the specific arrangements and density of defect centres in comparison with microcrystalline samples prepared by sintering at high temperature.[94] The mechanism is based on the reduction of Sm3+ to Sm2+ by trapping electrons that are created upon exposure to ionizing radiation in the BaFCl host. The 5 DJ-7 FJ f-f luminescence lines can be very efficiently excited via the parity allowed 4f6 →4f5 5d transition at around 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)).[95] The phosphor has potential applications in personal dosimetry, dosimetry and imaging in radiotherapy, and medical imaging.[96]

Biological role

Samarium
Hazards
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Danger
H228, H261, H373
P210, P231+232, P422[97]
NFPA 704
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g., diesel fuelHealth code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g., sodium chlorideReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
2
0
2

Samarium salts stimulate metabolism, but it is unclear whether this is the effect of 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 about 8 µg/L being dissolved in the blood. Samarium is not absorbed by plants to a measurable concentration and therefore is normally not a 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.[10]

When ingested, only about 0.05% of samarium salts is absorbed into the bloodstream and the remainder is excreted. From the blood, about 45% goes to the liver and 45% is deposited on the surface of the bones where it remains for about 10 years; the balance 10% is excreted.[71]

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Bibliography

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External links

Isotopes of samarium

Naturally occurring samarium (62Sm) is composed of five stable isotopes, 144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived radioisotopes, 147Sm (half life: 1.06×1011 y) and 148Sm (7×1015 y), with 152Sm being the most abundant (26.75% natural abundance). 146Sm is also fairly long-lived (6.8×107 y), but is not long-lived enough to have survived in significant quantities from the formation of the Solar System on Earth, although it remains useful in radiometric dating in the Solar System as an extinct radionuclide.Other than the naturally occurring isotopes, the longest-lived radioisotopes are 151Sm, which has a half-life of 88.8 years, and 145Sm, which has a half-life of 340 days. All of the remaining radioisotopes have half-lives that are less than two days, and the majority of these have half-lives that are less than 48 seconds. This element also has twelve known isomers with the most stable being 141mSm (t1/2 22.6 minutes), 143m1Sm (t1/2 66 seconds) and 139mSm (t1/2 10.7 seconds).

The long lived isotopes,146Sm, 147Sm, and 148Sm primarily decay by alpha decay to isotopes of neodymium. Lighter unstable isotopes of samarium primarily decay by electron capture to isotopes of promethium, while heavier ones decay by beta decay to isotopes of europium.

Isotopes of samarium are used in samarium–neodymium dating for determining the age relationships of rocks and meteorites.

151Sm is a medium-lived fission product and acts as a neutron poison in the nuclear fuel cycle. The stable fission product 149Sm is also a neutron poison.

Lunar magma ocean

According to the giant impact hypothesis a large amount of energy was liberated in the formation of the Moon and it is inferred that as a result a large portion of the Moon was once completely molten, forming a lunar magma ocean. Evidence for the magma ocean hypothesis comes from the highly anorthositic compositions of the crust in the lunar highlands, as well as the existence of rocks with a high concentration of the geochemical component referred to as KREEP.

Ages of formation and crystallization of the lunar magma ocean have been constrained by studies of isotopes of hafnium, tungsten, samarium, and neodymium. The magma ocean formed about 70 million years after the history of the Solar System began, and most of the ocean had crystallized by about 215 million years after that beginning (Brandon, 2007).

Paul-Émile Lecoq de Boisbaudran

Paul-Émile Lecoq de Boisbaudran, also called François Lecoq de Boisbaudran (18 April 1838 – 28 May 1912), was a French chemist known for his discoveries of the chemical elements gallium, samarium and dysprosium.

Promethium

Promethium is a chemical element with symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500-600 grams naturally occurring in Earth's crust at any given time. Promethium is one of only two radioactive elements that are followed in the periodic table by elements with stable forms, the other being technetium. Chemically, promethium is a lanthanide. Promethium shows only one stable oxidation state of +3.

In 1902 Bohuslav Brauner suggested that there was a then-unknown element with properties intermediate between those of the known elements neodymium (60) and samarium (62); this was confirmed in 1914 by Henry Moseley who, having measured the atomic numbers of all the elements then known, found that atomic number 61 was missing. In 1926, two groups (one Italian and one American) claimed to have isolated a sample of element 61; both "discoveries" were soon proven to be false. In 1938, during a nuclear experiment conducted at Ohio State University, a few radioactive nuclides were produced that certainly were not radioisotopes of neodymium or samarium, but there was a lack of chemical proof that element 61 was produced, and the discovery was not generally recognized. Promethium was first produced and characterized at Oak Ridge National Laboratory in 1945 by the separation and analysis of the fission products of uranium fuel irradiated in a graphite reactor. The discoverers proposed the name "prometheum" (the spelling was subsequently changed), derived from Prometheus, the Titan in Greek mythology who stole fire from Mount Olympus and brought it down to humans, to symbolize "both the daring and the possible misuse of mankind's intellect". However, a sample of the metal was made only in 1963.

There are two possible sources for natural promethium: rare decays of natural europium-151 (producing promethium-147), and uranium (various isotopes). Practical applications exist only for chemical compounds of promethium-147, which are used in luminous paint, atomic batteries and thickness measurement devices, even though promethium-145 is the most stable promethium isotope. Because natural promethium is exceedingly scarce, it is typically synthesized by bombarding uranium-235 (enriched uranium) with thermal neutrons to produce promethium-147 as a fission product.

Rare-earth magnet

Rare-earth magnets are strong permanent magnets made from alloys of rare-earth elements. Developed in the 1970s and 1980s, rare-earth magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as ferrite or alnico magnets. The magnetic field typically produced by rare-earth magnets can exceed 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla. There are two types: neodymium magnets and samarium–cobalt magnets. Magnetostrictive rare-earth magnets such as Terfenol-D also have applications, e.g. in loudspeakers. Rare-earth magnets are extremely brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from breaking, chipping, or crumbling into powder.

The development of rare-earth magnets began around 1966, when K. J. Strnat and G. Hoffer of the US Air Force Materials Laboratory discovered that an alloy of yttrium and cobalt, YCo5, had by far the largest magnetic anisotropy constant of any material then known. The term "rare earth" can be misleading, as these metals are not particularly rare or precious; they are about as abundant as tin or lead. However rare earth ores are unevenly distributed, with the major source being China, which has led countries to classify rare earth metals as strategically important. Recent Chinese export restrictions on these materials have led other countries to initiate research programs to develop strong magnets that do not require them.

Samarium(II) bromide

Samarium(II) bromide is a crystalline compound with the chemical formula SmBr2. Samarium(II) bromide is a brown crystal at room temperature.

Samarium(II) chloride

Samarium(II) chloride (SmCl2) is a chemical compound, used as a radical generating agent in the ketone-mediated intraannulation reaction.

Samarium(II) iodide

Samarium(II) iodide is an inorganic compound with the formula SmI2. When employed as a solution for organic synthesis, it is known as "Kagan's reagent". SmI2 is a green solid and its solutions are green as well. It is a strong one-electron reducing agent that is used in organic synthesis.

Samarium(III) bromide

Samarium(III) bromide is a crystalline compound of one samarium and three bromine atoms. Samarium tribromide is a dark brown powder at room temperature.

Samarium(III) chloride

Samarium(III) chloride, also known as samarium trichloride, is an inorganic compound of samarium and chloride. It is a pale yellow solid that rapidly absorbs water to form a hexahydrate, SmCl3.6H2O. The compound has few practical applications but is used in laboratories for research on new compounds of samarium.

Samarium(III) fluoride

Samarium(III) fluoride (SmF3) is a slightly hygroscopic solid fluoride.

At room temperature, it has orthorhombic structure with space group Pnma – β-YF3 type with lattice constants a = 666,9 pm, b = 705,9 pm, c = 440,5 pm. Above 495 °C, it has the rhombohedral LaF3 structure (space group P3cl) – with lattice constants a = 707, c = 724 pm.Conditions/substances to avoid are: open flame, moisture, strong acids.

Samarium(III) oxide

Samarium(III) oxide (Sm2O3) is a chemical compound.

Samarium(III) sulfide

Samarium(III) sulfide (Sm2S3) is a chemical compound.

Samarium (153Sm) lexidronam

Samarium (153Sm) lexidronam (chemical name Samarium-153-ethylene diamine tetramethylene phosphonate, abbreviated Samarium-153 EDTMP, trade name Quadramet) is a chelated complex of a radioisotope of the element samarium with EDTMP. It is used to treat pain when cancer has spread to the bone.It is injected into a vein and distributed throughout the body, where it is preferentially absorbed in areas where cancer has invaded the bone. The radioisotope 153Sm, with a half-life of 46.3 hours, decays by emitting beta particles (electrons), which kill the nearby cells. Pain begins to improve in the first week for most people and the effects can last several months. It is commonly used in lung cancer, prostate cancer, breast cancer, and osteosarcoma.

Samarium monochalcogenides

Samarium monochalcogenides are chemical compounds with the composition SmX, where Sm stands for the lanthanide element samarium and X denotes any one of three chalcogen elements, sulfur, selenium or tellurium, resulting in the compounds SmS, SmSe or SmTe. In these compounds, samarium formally exhibits oxidation state +2, whereas it usually assumes the +3 state, resulting in chalcogenides with the chemical formula Sm2X3.

Samarium–cobalt magnet

A samarium–cobalt (SmCo) magnet, a type of rare earth magnet, is a strong permanent magnet made of two basic elements samarium and cobalt. Actually, samarium is substituted by a portion of other rare earth elements including praseodymium, cerium and gadolinium, and cobalt is substituted by a portion of other transition metals including iron, copper and zirconium. They are available in two "series", namely SmCo5 magnets and Sm2Co17 magnets. They were developed in the early 1960s based on work done by Karl Strnat and Alden Ray at Wright-Patterson Air Force Base and the University of Dayton, respectively. In particular, Strnat and Ray developed the first formulation of SmCo5. They are generally ranked similarly in strength to neodymium magnets, but have higher temperature ratings and higher coercivity. They are brittle, and prone to cracking and chipping. Samarium–cobalt magnets have maximum energy products (BHmax) that range from 14 megagauss-oersteds (MG·Oe) to 33 MG·Oe, that is approx. 112 kJ/m3 to 264 kJ/m3; their theoretical limit is 34 MG·Oe, about 272 kJ/m3.

Sintered Samarium Cobalt magnets exhibit magnetic anisotropy, meaning they can only be magnetized in the axis of their magnetic orientation. This is done by aligning the crystal structure of the material during the manufacturing process.

Samarium–neodymium dating

Samarium–neodymium dating is a radiometric dating method useful for determining the ages of rocks and meteorites, based on radioactive decay of a long-lived samarium (Sm) isotope to a radiogenic neodymium (Nd) isotope. Neodymium isotope ratios together with samarium-neodymium ratios are used to provide information on the source of igneous melts, as well as to provide age information. It is sometimes assumed that at the moment when crustal material is formed from the mantle the neodymium isotope ratio depends only on the time when this event occurred, but thereafter it evolves in a way that depends on the new ratio of samarium to neodymium in the crustal material, which will be different from the ratio in the mantle material. Samarium–neodymium dating allows us to determine when the crustal material was formed.

The usefulness of Sm–Nd dating stems from the fact that these two elements are rare earths and are thus, theoretically, not particularly susceptible to partitioning during sedimentation and diagenesis. Fractional crystallisation of felsic minerals changes the Sm/Nd ratio of the resultant materials. This, in turn, influences the rate at which the 143Nd/144Nd ratio increases due to production of radiogenic 143Nd.

In many cases, Sm–Nd and Rb–Sr isotope data are used together.

Samarskite-(Y)

Samarskite is a radioactive rare earth mineral series which includes

samarskite-(Y) with formula: (YFe3+Fe2+U,Th,Ca)2(Nb,Ta)2O8

and samarskite-(Yb) with formula (YbFe3+)2(Nb,Ta)2O8. The formula for samarskite-(Y) is also given as: (Y,Fe3+,U)(Nb,Ta)O4.Samarskite crystallizes in the orthorhombic - dipyramidal class as black to yellowish brown stubby prisms although it is typically found as anhedral masses. Specimens with a high uranium content are typically metamict and appear coated with a yellow brown earthy rind.

Samarskite occurs in rare earth bearing granite pegmatites with other rare minerals. It occurs in association with columbite, zircon, monazite, uraninite, aeschynite, magnetite, albite, topaz, beryl, garnet, muscovite and biotite.Samarskite was first described in 1847 for an occurrence in Miass, Ilmen Mountains, Southern Ural Mountains of Russia. The chemical element samarium was first isolated from a specimen of samarskite in 1879. Samarium was named after samarskite which was named for the Russian mine official, Colonel Vasili Samarsky-Bykhovets (1803–1870).Samarskite-(Yb) was first described in 2004 for an occurrence in the South Platte Pegmatite District, Jefferson County, Colorado.

Vintage Noiseless

The Vintage Noiseless series is a line of electric guitar pickups made by Fender. Introduced in 1998, they feature a stacked-coil design. The range includes models for electric guitars and basses. The Vintage Noiseless pickups were an original equipment material on the American Deluxe series instruments made between 1998 and 2003. They are now widely used on many Mexican-made and Custom Shop guitars such as the Eric Clapton and Jeff Beck signature models since 2001.

Formula color symmetry space group No Pearson symbol a (pm) b (pm) c (pm) Z density,
g/cm3
Sm silvery trigonal[4] R3m 166 hR9 362.9 362.9 2621.3 9 7.52
Sm silvery hexagonal[4] P63/mmc 194 hP4 362 362 1168 4 7.54
Sm silvery tetragonal[15] I4/mmm 139 tI2 240.2 240.2 423.1 2 20.46
SmO golden cubic[16] Fm3m 225 cF8 494.3 494.3 494.3 4 9.15
Sm2O3 trigonal[17] P3m1 164 hP5 377.8 377.8 594 1 7.89
Sm2O3 monoclinic[17] C2/m 12 mS30 1418 362.4 885.5 6 7.76
Sm2O3 cubic[18] Ia3 206 cI80 1093 1093 1093 16 7.1
SmH2 cubic[19] Fm3m 225 cF12 537.73 537.73 537.73 4 6.51
SmH3 hexagonal[20] P3c1 165 hP24 377.1 377.1 667.2 6
Sm2B5 gray monoclinic[21] P21/c 14 mP28 717.9 718 720.5 4 6.49
SmB2 hexagonal[22] P6/mmm 191 hP3 331 331 401.9 1 7.49
SmB4 tetragonal[23] P4/mbm 127 tP20 717.9 717.9 406.7 4 6.14
SmB6 cubic[24] Pm3m 221 cP7 413.4 413.4 413.4 1 5.06
SmB66 cubic[25] Fm3c 226 cF1936 2348.7 2348.7 2348.7 24 2.66
Sm2C3 cubic[26] I43d 220 cI40 839.89 839.89 839.89 8 7.55
SmC2 tetragonal[26] I4/mmm 139 tI6 377 377 633.1 2 6.44
SmF2 purple[27] cubic[28] Fm3m 225 cF12 587.1 587.1 587.1 4 6.18
SmF3 white[27] orthorhombic[28] Pnma 62 oP16 667.22 705.85 440.43 4 6.64
SmCl2 brown[27] orthorhombic[29] Pnma 62 oP12 756.28 450.77 901.09 4 4.79
SmCl3 yellow[27] hexagonal[28] P63/m 176 hP8 737.33 737.33 416.84 2 4.35
SmBr2 brown[27] orthorhombic[30] Pnma 62 oP12 797.7 475.4 950.6 4 5.72
SmBr3 yellow[27] orthorhombic[31] Cmcm 63 oS16 404 1265 908 2 5.58
SmI2 green[27] monoclinic P21/c 14 mP12
SmI3 orange[27] trigonal[32] R3 63 hR24 749 749 2080 6 5.24
SmN cubic[33] Fm3m 225 cF8 357 357 357 4 8.48
SmP cubic[34] Fm3m 225 cF8 576 576 576 4 6.3
SmAs cubic[35] Fm3m 225 cF8 591.5 591.5 591.5 4 7.23
Samarium compounds
Samarium(II)
Samarium(III)

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