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Samarium in the periodic table
silvery white
General properties
Name, symbol, number samarium, Sm, 62
Pronunciation /səˈmɛəriəm/ sə-MAIR-ee-əm
Element category lanthanide
Group, period, block n/a, 6, f
Standard atomic weight 150.36
Electron configuration [Xe] 6s2 4f6
2, 8, 18, 24, 8, 2
Physical properties
Phase solid
Density (near r.t.) 7.52 g·cm−3
Liquid density at m.p. 7.16 g·cm−3
Melting point 1345 K, 1072 °C, 1962 °F
Boiling point 2173 K, 1900 °C, 3452 °F
Heat of fusion 8.62 kJ·mol−1
Heat of vaporization 192 kJ·mol−1
Molar heat capacity 29.54 J·mol−1·K−1
Vapor pressure
Atomic properties
Oxidation states 4, 3, 2, 1

(mildly basic oxide)

Electronegativity 1.17 (Pauling scale)
Ionization energies 1st: 544.5 kJ·mol−1
2nd: 1070 kJ·mol−1
3rd: 2260 kJ·mol−1
Atomic radius 180 pm
Covalent radius 198±8 pm
Crystal structure rhombohedral
Samarium has a rhombohedral crystal structure
Magnetic ordering paramagnetic[1]
Thermal conductivity 13.3 W·m−1·K−1
Speed of sound (thin rod) (20 °C) 2130 m·s−1
Young's modulus (α form) 49.7 GPa
Shear modulus (α form) 19.5 GPa
Bulk modulus (α form) 37.8 GPa
Poisson ratio (α form) 0.274
Vickers hardness 412 MPa
Brinell hardness 441 MPa
CAS registry number 7440-19-9
Discovery Lecoq de Boisbaudran (1879)
First isolation Lecoq de Boisbaudran (1879)
Most stable isotopes
Main article: Isotopes of samarium
iso NA half-life DM DE (MeV) DP
144Sm 3.07% - (β+β+) 1.7811 144Nd
(α) 0.0761 140Nd
145Sm syn 340 d ε - 145Pm
146Sm trace 1.03×108 y α 2.529 142Nd
147Sm 14.99% 1.06×1011 y α 2.310 143Nd
148Sm 11.24% 7×1015 y α 1.986 144Nd
149Sm 13.82% >2×1015 y (α) 1.870 145Nd
150Sm 7.38% - (α) 1.4495 146Nd
151Sm syn 90 y β - 151Eu
152Sm 26.75% - (α) 0.2203 148Nd
153Sm syn 46.284 h β - 153Eu
154Sm 22.75% >2.3×1018 y (ββ) 1.2510 154Gd
· references


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 Vasili 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 such metals 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 (1292 °F), without losing their magnetic properties. The radioactive isotope samarium-153 is the major 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 an X-ray laser.

Physical properties[edit]

Samarium is a rare earth metal having the 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 trigonal structure (α form). Upon heating to 731 °C, its crystal symmetry changes into hexagonal 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-hexagonal 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.[2] 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.[2]

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.[3][4] Individual samarium atoms can be isolated by encapsulating them into fullerene molecules.[5] They can also be doped between the C60 molecules in the fullerene solid, rendering it superconductive at temperatures below 8 K.[6] Samarium doping of iron-based superconductors – the most recent class of high-temperature superconductors – allows to enhance their transition temperature to 56 K, which is the highest value achieved so far in this series.[7]

Chemical properties[edit]

Freshly prepared samarium has a silvery luster. In air, it slowly oxidizes at room temperature and spontaneously ignites at 150 °C.[8][9] 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 dissolves readily in dilute sulfuric acid to form solutions containing the yellow[11] to pale green Sm(III) ions, which exist as [Sm(OH2)9]3+ complexes:[10]

(aq) + 3 H2 (g)









Samarium metal reacts with all the halogens X = F, Cl, Br or I, forming trihalides:[37]


Their further reduction with samarium, lithium or sodium metals at elevated temperatures (about 700–900 °C) yields dihalides.[27] The diiodide can also be prepared by heating SmI3, or by reacting the metal with 1,2-diiodoethane in anhydrous tetrahydrofuran at room temperature:[38]


In addition to dihalides, the reduction also produces numerous non-stoichiometric samarium halides with a well-defined crystal structure, such as Sm3F7, Sm14F33, Sm27F64,[26] Sm11Br24, Sm5Br11 and Sm6Br13.[39]

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),[40] and similar treatment results in a new phase of samarium triiodide (density 5.97 g/cm3).[41]



Samarium hexaboride[edit]


New research seems to show that it may be a Topological insulator.[45][46][47]

Other inorganic compounds[edit]

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.[24] 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.[32] Similar procedure is adopted for the monarsenide SmAs, but the synthesis temperature is higher at 1800 °C.[33]

A large number of crystalline binary compounds are known for samarium and one of the group-4, 5 or 6 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.[48][49][50]

Organometallic compounds[edit]



Alkyls and aryls of samarium are obtained through a metathesis reaction in tetrahydrofuran or ether:[51]

SmCl3 + 3 LiR → SmR3 + 3 LiCl

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


Main article: Isotopes of samarium

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 t½ = 1.06×1011 years), 148Sm (7×1015 years) and 149Sm (>2×1015 years), with 152Sm being the most abundant (natural abundance 26.75%).[53] 149Sm is listed by various sources either as stable[53][54] or radioactive isotope.[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 of 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 (t½ = 66 seconds) and 139mSm (t½ = 10.7 seconds).[53]


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.[56][57] 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.[9] The Swiss chemist Marc Delafontaine announced a new element decipium (from Latin: decipiens meaning "deceptive, misleading") in 1878,[58][59] but later in 1880–1881 demonstrated that it was a mixture of several elements, one being identical to the Boisbaudran's samarium.[60][61] 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.[62]

Boisbaudran named his element samaria after the mineral samarskite, which in turn honored Vasili 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.[63][64][65] In this sense samarium was the first chemical element to be named after a person.[62][66] 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.[62][67]


Occurrence and production[edit]



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%)[9] 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.[8] 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)[69] and India (2,700 tonnes).[70] Samarium is usually sold as oxide, which at the price of about 30 USD/kg is one of the cheapest lanthanide oxides.[68] 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).[57]



Barbier reaction using SmI2


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.[9] 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.[71] 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.[72]


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.[8] The corresponding drug has several names including samarium (153Sm) lexidronam; its trade name is Quadramet.[73][74][75]

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 hundred barns for 150Sm, 152Sm, and 153Sm, and is 6,800 barns for natural (mixed-isotope) samarium.[9][69][76] 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.[77]

Non-commercial and potential applications[edit]



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,[81] and such devices are being developed commercially.[82] Samarium monosulfide also generates electric voltage upon moderate heating to about 150 °C that can be applied in thermoelectric power converters.[83]

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.[84]

Health issues[edit]

Samarium metal has no biological role in human body. Its 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 micrograms, mostly in liver and kidneys and with about 8 micrograms per liter 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.[8]



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  • Greenwood, Norman N. and Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed. ed.). Butterworth–Heinemann. ISBN 0080379419. 

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