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Terbium is a chemical element; it has symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable and ductile. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with water, evolving hydrogen gas. Terbium is never found in nature as a free element, but it is contained in many , including cerite, gadolinite, monazite, xenotime and euxenite.
Swedish chemist Carl Gustaf Mosander discovered terbium as a chemical element in 1843. He detected it as an impurity in yttrium oxide (). Yttrium and terbium, as well as erbium and ytterbium, are named after the village of Ytterby in Sweden. Terbium was not isolated in pure form until the advent of ion exchange techniques.
Terbium is used to dopant calcium fluoride, calcium tungstate and strontium molybdate in solid-state devices, and as a crystal stabilizer of that operate at elevated temperatures. As a component of Terfenol-D (an alloy that expands and contracts when exposed to magnetic fields more than any other alloy), terbium is of use in , in naval sonar systems and in . Terbium is considered non-hazardous, though its biological role and toxicity have not been researched in depth.
Most of the world's terbium supply is used in green . Terbium oxide is used in and television and monitor (CRTs). Terbium green phosphors are combined with divalent europium blue phosphors and trivalent europium red phosphors to provide trichromatic lighting technology, a high-efficiency white light used in indoor lighting.
The terbium(III) cation (Tb3+) is brilliantly Fluorescence, in a bright lemon-yellow color that is the result of a strong green emission line in combination with other lines in the orange and red. The yttrofluorite variety of the mineral fluorite owes its creamy-yellow fluorescence in part to terbium. Terbium easily oxidizes, and is therefore used in its elemental form specifically for research. Single terbium atoms have been isolated by implanting them into fullerene molecules. Trivalent europium (Eu3+) and Tb3+ ions are among the lanthanide ions that have garnered the most attention because of their strong luminosity and great color purity.V.B. Taxak, R. Kumar, J.K. Makrandi, S.P. Khatkar Displays, 30 (2009), pp. 170–174
Terbium has a simple ferromagnetic ordering at temperatures below 219 K. Above 219 K, it turns into a Helimagnetism state in which all of the atomic moments in a particular basal plane layer are parallel and oriented at a fixed angle to the moments of adjacent layers. This antiferromagnetism transforms into a disordered paramagnetic state at 230 K.
The most common oxidation state of terbium is +3 (trivalent), such as in . In the solid state, tetravalent terbium is also known, in compounds such as terbium oxide () and terbium tetrafluoride. In solution, terbium typically forms trivalent species, but can be oxidized to the tetravalent state with ozone in highly basic aqueous conditions.
The coordination and organometallic chemistry of terbium is similar to other lanthanides. In aqueous conditions, terbium can be coordinated by nine water molecules, which are arranged in a tricapped trigonal prismatic molecular geometry. Complexes of terbium with lower coordination number are also known, typically with bulky ligands like bis(trimethylsilyl)amide, which forms the three-coordinate trisN,N-bis(trimethylsilyl)amideterbium(III) () complex.
Most coordination and organometallic complexes contain terbium in the trivalent oxidation state. Divalent Tb2+ complexes are also known, usually with bulky cyclopentadienyl-type ligands. A few coordination compounds containing terbium in its tetravalent state are also known.
Terbium(IV) fluoride () is the only halide that tetravalent terbium can form. It has strong oxidizing properties and is a strong halogenation, emitting relatively pure atomic fluorine when heated, rather than the mixture of fluoride vapors emitted from cobalt(III) fluoride or cerium(IV) fluoride. It can be obtained by reacting terbium(III) chloride or terbium(III) fluoride with fluorine gas at 320 °C:
Terbium(III) oxide or terbia is the main oxide of terbium, and appears as a dark brown water-insoluble solid. It is slightly hygroscopic and is the main terbium compound found in rare earth-containing minerals and clays.
Other compounds include:
The element also has 31 , with masses of 141–154, 156, 158, 162, and 164–168 (not every mass number corresponds to only one isomer). The most stable of them are terbium-156m2, with a half-life of 24.4 hours, and terbium-154m2, with a half-life of 22.7 hours; this is more stable than ground states of terbium isotopes, except outside the mass range 155–161.
Terbium-149, with its half-life of 4.1 hours, is a promising candidate in targeted alpha therapy and positron emission tomography.
Mosander first separated yttria into three fractions, all named for the ore: yttria, erbia, and terbia. "Terbia" was originally the fraction that contained the pink color, due to the element now known as erbium. "Erbia", the oxide containing what is now known as terbium, originally was the fraction that was yellow or dark orange in solution. The insoluble oxide of this element was noted to be tinged brown, and soluble oxides after combustion were noted to be colorless. Until the advent of spectral analysis, arguments went back and forth as to whether erbia even existed. Spectral analysis by Marc Delafontaine allowed the separate elements and their oxides to be identified, but in his publications, the names of erbium and terbium were switched, following a brief period where terbium was renamed "mosandrum", after Mosander. The names have remained switched ever since.
The early years of preparing terbium (as terbium oxide) were difficult. Metal oxides from gadolinite and samarskite were dissolved in nitric acid, and the solution was further separated using oxalic acid and potassium sulfate. There was great difficulty in separating erbia from terbia; in 1881, it was noted that there was no satisfactory method to separate the two. By 1914, different solvents had been used to separate terbium from its host minerals, but the process of separating terbium from its neighbor elements - gadolinium and dysprosium - was described as "tedious" but possible. Modern terbium extraction methods are based on the liquid–liquid extraction process developed by Werner Fischer et al., in 1937.
Terbium (as the species Tb II) has been detected in the atmosphere of KELT-9b, a hot-Jupiter exoplanet.
Currently, the richest commercial sources of terbium are the ion-adsorption of southern China; the concentrates with about two-thirds yttrium oxide by weight have about 1% terbia. Small amounts of terbium occur in bastnäsite and monazite; when these are processed by solvent extraction to recover the valuable heavy lanthanides as samarium-europium-gadolinium concentrate, terbium is recovered therein. Due to the large volumes of bastnäsite processed relative to the ion-adsorption clays, a significant proportion of the world's terbium supply comes from bastnäsite.
In 2018, a rich terbium supply was discovered off the coast of Japan's Minamitori Island, with the stated supply being "enough to meet the global demand for 420 years".
The most efficient separation routine for terbium salt from the rare-earth salt solution is ion exchange. In this process, rare-earth ions are adsorption onto suitable ion-exchange resin by exchange with hydrogen, ammonium or cupric ions present in the resin. The rare earth ions are then selectively washed out by suitable Complexing agent. As with other rare earths, terbium metal is produced by reducing the anhydrous chloride or fluoride with calcium metal. Calcium and tantalum impurities can be removed by vacuum remelting, distillation, amalgam formation or zone melting.
In 2020, the annual demand for terbium was estimated at . Terbium is not distinguished from other rare earths in the United States Geological Survey's Mineral Commodity Summaries, which in 2024 estimated the global reserves of rare earth minerals at .
Terbium is also used in and in the production of electronic devices. As a component of Terfenol-D, terbium is used in , in naval sonar systems, , and other magnetomechanical devices. Terfenol-D is a terbium alloy that expands or contracts in the presence of a magnetic field. It has the highest magnetostriction of any alloy. It is used to increase verdet constant in long-distance fiber optic communication. Terbium-doped garnets are also used in optical isolators, which prevents reflected light from traveling back along the optical fiber.
Terbium oxides are used in green in fluorescent lamps, color TV tubes, and flat screen monitors. Terbium, along with all other Lanthanide except lanthanum and lutetium, is Luminescence in the 3+ oxidation state. The brilliant fluorescence allows terbium to be used as a Chemical probe in biochemistry, where it somewhat resembles calcium in its behavior. Terbium "green" phosphors (which fluoresce a brilliant lemon-yellow) are combined with divalent europium blue phosphors and trivalent europium red phosphors to provide trichromatic lighting, which is by far the largest consumer of the world's terbium supply. Trichromatic lighting provides much higher light output for a given amount of electrical energy than does incandescent lighting.
In 2023, terbium compounds were used to create a lattice with a single iron atom that was then examined by synchrotron x-ray beam. This was the first successful attempt to characterize a single atom at sub-atomic levels.
Reviews of the toxicity of the rare earth elements place terbium and its compounds as "of low to moderately toxicity", remarking on the lack of detailed studies on their hazards and the lack of market demand forestalling evidence of toxicity.
Some studies demonstrate environmental accumulation of terbium as hazardous to fish and plants. High exposures of terbium may enhance the toxicity of other substances causing endocytosis in Plant cell.
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