Samarium

Samarium is a chemical element with the symbol Sm and atomic number 62. It is a moderately hard, silvery metal that belongs to the lanthanide series.

In its pure form, samarium slowly oxidizes when exposed to air. This oxidation causes its bright, silvery lustre to turn into a duller appearance. Samarium is considered a rare earth element. It has a density and hardness similar to the metal zinc. One of its most striking physical features is its atomic radius. At 238 pm, samarium has one of the largest atomic radii of all elements. Only five other elements, including potassium and caesium, have larger radii.

The physical structure of samarium changes depending on temperature and pressure. In normal ambient conditions, it exists in a rhombohedral structure called the α form. When the metal is heated to 373 K, its crystal symmetry shifts to a hexagonal close-packed (hcp) structure. If heating continues to 658 K, it transforms into a body-centered cubic (bcc) phase. High pressure also forces the atoms into new arrangements. Applying 40 kbar of pressure results in a double-hexagonally close-packed (dhcp) structure. At much higher pressures, such as 900 kbar, a tetragonal phase appears. These shifts show how sensitive the metal's internal organization is to its environment.

Chemically, samarium is quite versatile and can exist in different oxidation states. While it usually has a +3 oxidation state, it is one of the few lanthanides that can also reach a +2 state.

This makes it useful as a reducing agent, which is a substance that helps transfer electrons in chemical synthesis. For example, samarium(II) iodide is a common tool in laboratories. Samarium also reacts with water. It reacts slowly with cold water, but it reacts rapidly with hot water to create samarium hydroxide. To prevent it from oxidizing too quickly, scientists often seal samarium under an inert gas like argon. This preserves its metallic look.

Samarium is found in several different minerals in nature. It can appear in concentrations of up to 2.8% in minerals like cerite, gadolinite, and monazite.

The most common commercial sources for the element are monazite and bastnäsite. These minerals are mined in various parts of the world, including the United States, Brazil, India, Sri Lanka, and Australia. China is currently the global leader in both the mining and production of samarium. This makes the element's supply chain heavily centered in that region.

The history of samarium's discovery is tied to both chemistry and naming traditions. The French chemist Paul-Émile Lecoq de Boisbaudran discovered the element in 1879.

He named it after the mineral samarskite. This mineral was named to honor a Russian mine official, Colonel Vassili Samarsky-Bykhovets. Because of this connection, Samarsky-Bykhovets became the first person to have a chemical element named after him, even though the name was indirect. This discovery helped scientists better understand the properties of the lanthanide series.

Samarium has several critical applications in modern technology and medicine. Its most common commercial use is in the production of samarium–cobalt magnets. These magnets have permanent magnetization that is second only to neodymium magnets.

However, samarium–cobalt magnets have a major advantage: they can withstand temperatures above 100 °C without losing their magnetic properties. In the field of nuclear energy, the isotope samarium-149 is used as a neutron absorber. It is added to the control rods of nuclear reactors to manage the reaction. It also forms naturally during reactor operation, which engineers must consider when designing these systems.

Medical science also uses specific isotopes of this element to treat illness. The radioisotope samarium-153 is the active part of a drug called lexidronam.

This drug is used to kill cancer cells in several areas, including the lungs, prostate, and breasts, as well as in osteosarcoma. Beyond medicine, samarium is used in X-ray lasers and for radioactive dating. It even shows interesting behavior in superconductivity. When samarium is used to "dope" or add to iron-based superconductors, it can increase their transition temperature to 56 K. This is the highest value ever achieved in that specific class of materials.