Samarium (Sm)

Discovery & history

Discovered: 1879 · Paul-Émile Lecoq de Boisbaudran

Detection of samarium and related elements was announced by several scientists in the second half of the 19th century; however, most sources give priority to French chemist Paul-Émile Lecoq de Boisbaudran. Boisbaudran isolated samarium oxide and/or hydroxide in Paris in 1879 from the mineral samarskite ((Y,Ce,U,Fe)3(Nb,Ta,Ti)5O16) and identified a new element in it via sharp optical absorption lines. Swiss chemist Marc Delafontaine announced a new element decipium (from Latin: decipiens meaning "deceptive, misleading") in 1878, but later in 1880–1881 demonstrated that it was a mix of several elements, one being identical to Boisbaudran's samarium. Though samarskite was first found in the Ural Mountains in Russia, by the late 1870s it had been found in other places, making it available to many researchers. In particular, it was found that the samarium isolated by Boisbaudran was also impu

Uses & applications

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 1,900 °C (3,450 °F) converts it to the more stable monoclinic phase. Cubic Sm2O3 has also been described. Samarium is one of the few lanthanides that form a monoxide, SmO. This lustrous golden-yellow compound was obtain

Isotopes

Naturally occurring samarium is composed of five stable isotopes: 144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived radioisotopes, 147Sm (half-life t1/2 = 1.066×1011 years) and 148Sm (6.3×1015 years), with 152Sm being the most abundant (26.75%). 149Sm is listed by various sources as being stable, but some sources state that it is radioactive; the lower bound on its half-life is 2×1015 years. Some observationally stable samarium isotopes are predicted to decay to isotopes of neodymium. The long-lived isotopes 146Sm, 147Sm, and 148Sm (and 149Sm if it decays) undergo alpha decay to neodymium isotopes. Lighter unstable isotopes of samarium mainly decay by electron capture to promethium, while heavier ones beta decay to europium. The known isotopes range from 129Sm to 168Sm. The half-lives of 151Sm and 145Sm are 94.6 years and 340 days, respectively. All remaining radioisotop