A rare earth element (REE) or rare earth metal (REM), as defined byIUPAC, is one of a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides,as well as scandium and yttrium.Scandium and yttrium are considered rare earth elements because they tend to occur in the same ore deposits as the lanthanides and exhibit similar chemical properties.
Rare earth elements are cerium (Ce), dysprosium(Dy), erbium (Er),europium(Eu), gadolinium(Gd), holmium(Ho), lanthanum(La), lutecium(Lu),neodymium(Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc),terbium (Tb), thulium (Tm),ytterbium (Yb) and yttrium (Y).
Despite their name, rare earth elements are – with the exception of the radioactive promethium – relatively plentiful in Earth`s crust, with cerium being the 25th most abundant elment at 68 parts per million, or as abundant as copper. They are not especially rare, but they tend to occur together in nature and are difficult to separate from one another. However, because of their geochemical properties, rare earth elements are typically dispersed and not often found concentrated as rare earth minerals in economically exploitable ore deposits.The first such mineral discovered was gadolinite, a mineral composed of cerium, yttrium, iron, silicon and other elements. This mineral was extracted from a mine in the village of Ytterby in Sweden; four of the rare earth elements bear names derived from this single location.
A table listing the seventeen rare earth elements, their atomic number and symbol, the etymology of their names, and their main usages (see also Applications of lanthanides) is provided here. Some of the rare earth elements are named after the scientists who discovered or elucidated their elemental properties, and some after their geographical discovery.
|39||Y||Yttrium||after the village of Ytterby, Sweden, where the first rare earth ore was discovered.||Yttrium aluminium garnet (YAG) laser, yttrium vanadate (YVO4) as host for europium in television red phosphor, YBCO high-temperature superconductors, yttria-stabilized zirconia(YSZ), yttrium iron garnet (YIG) microwave filters,energy-efficient light bulbs,spark plugs, gas mantles, additive to steel|
|70||Yb||Ytterbium||after the village of Ytterby, Sweden.||Infrared lasers, chemical reducing agent, decoy flares, stainless steel, stress gauges, nuclear medicine|
|69||Tm||Thulium||after the mythological northern land of Thule.||Portable X-ray machines, metal-halide lamps, lasers|
|65||Tb||Terbium||after the village of Ytterby, Sweden.||Additive in Neodymium based magnets, Green phosphors, lasers, fluorescent lamps, magnetostrictive alloys such as Terfenol-D|
|21||Sc||Scandium||from Latin Scandia(Scandinavia).||Light aluminium-scandium alloys for aerospace components, additive in metal-halide lampsand mercury-vapor lamps,radioactive tracing agent in oil refineries|
|62||Sm||Samarium||after mine official, Vasili Samarsky-Bykhovets.||Rare-earth magnets, lasers, neutron capture, masers|
|61||Pm||Promethium||after the TitanPrometheus, who brought fire to mortals.||Nuclear batteries, luminous paint|
|59||Pr||Praseodymium||from the Greek "prasios", meaning leek-green, and "didymos", meaning twin.||Rare-earth magnets, lasers, core material for carbon arc lighting, colorant in glasses and enamels, additive in didymium glass used in welding goggles,ferrocerium firesteel(flint) products.|
|60||Nd||Neodymium||from the Greek "neos", meaning new, and "didymos", meaning twin.||Rare-earth magnets, lasers, violet colors in glass and ceramics, didymium glass, ceramic capacitors|
|71||Lu||Lutetium||after Lutetia, the city that later became Paris.||Positron emission tomography – PET scan detectors, high-refractive-index glass, lutetium tantalate hosts for phosphors|
|57||La||Lanthanum||from the Greek "lanthanein", meaning to be hidden.||High refractive index and alkali-resistant glass, flint, hydrogen storage, battery-electrodes, camera lenses, fluid catalytic cracking catalyst for oil refineries|
|67||Ho||Holmium||after Stockholm (in Latin, "Holmia"), native city of one of its discoverers.||Lasers, wavelength calibration standards for optical spectrophotometers, magnets|
|64||Gd||Gadolinium||after Johan Gadolin(1760–1852), to honor his investigation of rare earths.||High refractive index glass or garnets, lasers, X-ray tubes, computer memories, neutron capture, MRI contrast agent, NMR relaxation agent, magnetostrictive alloys such as Galfenol, steel additive|
|63||Eu||Europium||after the continent of Europe.||Red and blue phosphors, lasers, mercury-vapor lamps, fluorescent lamps, NMR relaxation agent|
|68||Er||Erbium||after the village of Ytterby, Sweden.||Infrared lasers, vanadium steel, fiber-optic technology|
|66||Dy||Dysprosium||from the Greek "dysprositos", meaning hard to get.||Additive in Neodymium based magnets, lasers, magnetostrictive alloys such as Terfenol-D|
|58||Ce||Cerium||after the dwarf planet Ceres, named after the Roman goddess of agriculture.||Chemical oxidizing agent, polishing powder, yellow colors in glass and ceramics, catalyst for self-cleaning ovens, fluid catalytic cracking catalyst for oil refineries, ferroceriumflints for lighters|
The following abbreviations are often used:
· RE = rare earth
· REM = rare-earth metals
· REE = rare-earth elements
· REO = rare-earth oxides
· REY = rare-earth elements and yttrium
· LREE = light rare earth elements (Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd; also known as the cerium group)
· HREE = heavy rare earth elements (Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu; also known as the yttrium group)
The densities of the LREEs (as pure elements) range from 2.989 (scandium) to 7.9 g/cc (gadolinium), whereas those of the HREEs are from 8.2 to 9.8, except for yttrium (4.47) and ytterbium (between 6.9 and 7). The distinction between the groups is more to do with atomic volume and geological behavior (see lower down).