Europium is a chemical element with symbol Eu and atomic number 63. It was isolated in 1901 and is named after the continent of Europe.[4] It is a moderately hard, silvery metal which readily oxidizes in air and water. Being a typical member of the lanthanide series, europium usually assumes the oxidation state +3, but the oxidation state +2 is also common: all europium compounds with oxidation state +2 are slightly reducing. Europium has no significant biological role and is relatively non-toxic compared to other heavy metals. Most applications of europium exploit the phosphorescence of europium compounds. Europium is one of the least abundant elements in the universe, with only about 5×10−8% in the entire universe.[5]
Europium is a ductile metal with a hardness similar to that of lead. It crystallizes in a body-centered cubic lattice.[6] Some properties of europium are strongly influenced by its half-filled electron shell. Europium has the second lowest melting point and the lowest density of all lanthanides.[6]
Europium becomes a superconductor when it is cooled below 1.8 K and compressed to above 80 GPa. This is because europium is divalent in the metallic state,[7] and is converted into the trivalent state by the applied pressure. In the divalent state, the strong local magnetic moment (J = 7/2) suppresses the superconductivity, which is induced by eliminating this local moment (J = 0 in Eu3+).[8]
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