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Terbium, 65Tb
Pronunciation /ˈtɜːrbiəm/ (TUR-bee-əm)
Appearancesilvery white
Standard atomic weight Ar°(Tb)
Terbium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)65
Group f-block groups (no number)
Period period 6
Block   f-block
Electron configuration [ Xe ] 4f9 6s2
Electrons per shell2, 8, 18, 27, 8, 2
Physical properties
Phase at  STP solid
Melting point 1629  K (1356 °C,2473 °F)
Boiling point 3396 K(3123 °C,5653 °F)
Density (at 20° C)8.229 g/cm3 [3]
when liquid (at  m.p.)7.65 g/cm3
Heat of fusion 10.15  kJ/mol
Heat of vaporization 391 kJ/mol
Molar heat capacity 28.91 J/(mol·K)
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)17891979(2201)(2505)(2913)(3491)
Atomic properties
Oxidation states 0, [4] +1, [5] +2, +3, +4 (a weakly basic oxide)
Electronegativity Pauling scale: 1.2(?)
Ionization energies
  • 1st: 565.8 kJ/mol
  • 2nd: 1110 kJ/mol
  • 3rd: 2114 kJ/mol
Atomic radius empirical:177  pm
Covalent radius 194±5 pm
Terbium spectrum visible.png
Spectral lines of terbium
Other properties
Natural occurrence primordial
Crystal structure hexagonal close-packed (hcp)(hP2)
Lattice constants
Hexagonal close packed.svg
a = 360.56 pm
c = 569.66 pm (at 20 °C) [3]
Thermal expansion at  r.t. poly: 10.3 µm/(m⋅K)
Thermal conductivity 11.1 W/(m⋅K)
Electrical resistivity α, poly: 1.150 µΩ⋅m(at r.t.)
Magnetic ordering paramagnetic at 300 K
Molar magnetic susceptibility +146000×10−6 cm3/mol(273 K) [6]
Young's modulus 55.7 GPa
Shear modulus 22.1 GPa
Bulk modulus 38.7 GPa
Speed of sound thin rod2620 m/s(at 20 °C)
Poisson ratio 0.261
Vickers hardness 450–865 MPa
Brinell hardness 675–1200 MPa
CAS Number 7440-27-9
Namingafter Ytterby (Sweden), where it was mined
Discovery and first isolation Carl Gustaf Mosander (1843)
Isotopes of terbium
Main isotopes [7] Decay
abun­dance half-life (t1/2) mode pro­duct
157Tb synth 71 y ε 157Gd
158Tbsynth180 yε 158Gd
β 158Dy
159Tb100% stable
Symbol category class.svg  Category: Terbium
| references

Terbium is a chemical element; it has the 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 minerals, 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, Y2O3. 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 dope calcium fluoride, calcium tungstate and strontium molybdate in solid-state devices, and as a crystal stabilizer of fuel cells 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 actuators, in naval sonar systems and in sensors.

Most of the world's terbium supply is used in green phosphors. Terbium oxide is used in fluorescent lamps and television and monitor cathode-ray tubes (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 for standard illumination in indoor lighting.


Physical properties

Terbium is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife. [8] It is relatively stable in air compared to the earlier, more reactive lanthanides in the first half of the lanthanide series. [9] Terbium exists in two crystal allotropes with a transformation temperature of 1289 °C between them. [8] The 65 electrons of a terbium atom are arranged in the electron configuration [Xe]4f96s2. The eleven 4f and 6s electrons are valence. Only three electrons can be removed before the nuclear charge becomes too great to allow further ionization, but in the case of terbium, the stability of the half-filled [Xe]4f7 configuration allows further ionization of a fourth electron in the presence of very strong oxidizing agents such as fluorine gas. [8]

The terbium(III) cation is brilliantly fluorescent, 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 Eu3+ and Tb3+ ions are among the lanthanide ions that have garnered the most attention because of their strong luminosity and great color purity. [10] [11]

Terbium has a simple ferromagnetic ordering at temperatures below 219 K. Above 219 K, it turns into a helical antiferromagnetic 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 unusual antiferromagnetism transforms into a disordered paramagnetic state at 230 K. [12]

Chemical properties

Terbium metal is an electropositive element and oxidizes in the presence of most acids (such as sulfuric acid), all of the halogens, and even water. [13]

2 Tb (s) + 3 H2SO4 → 2 Tb3+ + 3 SO2−4 + 3 H2
2 Tb + 3 X2 → 2 TbX3 (X = F, Cl, Br, I)
2 Tb (s) + 6 H2O → 2 Tb(OH)3 + 3 H2

Terbium also oxidizes readily in air to form a mixed terbium(III,IV) oxide: [13]

8 Tb + 7 O2 → 2 Tb4O7

The most common oxidation state of terbium is +3 (trivalent), such as TbCl
. In the solid state, tetravalent terbium is also known, in compounds such as TbO2 and TbF4. [14] In solution, terbium typically forms trivalent species, but can be oxidized to the tetravalent state with ozone in highly basic aqueous conditions. [15]

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(trimethyl-silylamide), which forms the three-coordinate Tb[N(SiMe3)2]3 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. [16] [17] [18] A few coordination compounds containing terbium in its tetravalent state are also known. [19] [20] [21]

Oxidation states

Like most rare-earth elements and lanthanides, terbium is usually found in the +3 oxidation state. Like cerium and praseodymium, terbium can also form a +4 oxidation state, although it is unstable in water. [22] However, it is possible for terbium to also be found in the 0, +1 and +2 oxidation states.


Terbium sulfate, Tb2(SO4)3 (top), fluoresces green under ultraviolet light (bottom)

Terbium combines with nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon and arsenic at elevated temperatures, forming various binary compounds such as TbH2, TbH3, TbB2, Tb2S3 , TbSe, TbTe and TbN . [23] In those compounds, Tb mostly exhibits the oxidation states +3 and sometimes +2. Terbium(II) halides are obtained by annealing Tb(III) halides in presence of metallic Tb in tantalum containers. Terbium also forms sesquichloride Tb2Cl3, which can be further reduced to TbCl by annealing at 800 °C. This terbium(I) chloride forms platelets with layered graphite-like structure. [24]

Terbium(IV) fluoride is the only halide that tetravalent terbium can form, and has strong oxidizing properties. It is also a strong fluorinating agent, emitting relatively pure atomic fluorine when heated, rather than the mixture of fluoride vapors emitted from cobalt(III) fluoride or cerium(IV) fluoride. [25] It can be obtained by reacting terbium(III) chloride or terbium(III) fluoride with fluorine gas at 320 °C: [26]

2 TbF3 + F2 → 2 TbF4

When TbF4 and CsF is mixed in a stoichiometric ratio, in a fluorine gas atmosphere, CsTbF5 is obtained. It is an orthorhombic crystal, with space group Cmca, with a layered structure composed of [TbF8]4− and 11-coordinated Cs+. [27] The compound BaTbF6 can be prepared in a similar method. It is an orthorhombic crystal, with space group Cmma. The compound [TbF8]4− also exists. [28]

Other compounds include


Naturally occurring terbium is composed of its only stable isotope, terbium-159; the element is thus mononuclidic and monoisotopic. Thirty-six radioisotopes have been characterized, with the heaviest being terbium-171 (with an atomic mass of 170.95330(86) u) and lightest being terbium-135 (exact mass unknown). [29] The most stable synthetic radioisotopes of terbium are terbium-158, with a half-life of 180 years, and terbium-157, with a half-life of 71 years. All of the remaining radioactive isotopes have half-lives that are much less than a quarter of a year, and the majority of these have half-lives that are less than half a minute. [29] The primary decay mode before the most abundant stable isotope, 159Tb, is electron capture, which results in production of gadolinium isotopes, and the primary mode after is beta minus decay, resulting in dysprosium isotopes. [29]

The element also has 27 nuclear isomers, with masses of 141–154, 156, and 158 (not every mass number corresponds to only one isomer). The most stable of them are terbium-156m, with a half-life of 24.4 hours, and terbium-156m2, with a half-life of 22.7 hours; this is longer than half-lives of most ground states of radioactive terbium isotopes, except those with mass numbers 155–161. [29]

Terbium-149, with a half-life of 4.1 hours, is a promising candidate in targeted alpha therapy and positron emission tomography. [30] [31]


Carl Gustaf Mosander, the scientist who discovered terbium, lanthanum and erbium. Mosander Carl Gustav bw.jpg
Carl Gustaf Mosander, the scientist who discovered terbium, lanthanum and erbium.

Swedish chemist Carl Gustaf Mosander discovered terbium in 1843. He detected it as an impurity in yttrium oxide, Y2O3. Yttrium is named after the village of Ytterby in Sweden. Terbium was not isolated in pure form until the advent of ion exchange techniques. [32] [33] [34] :701 [35] [32] [36] [37]

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" (containing what is now known as terbium) originally was the fraction that was essentially colorless in solution. The insoluble oxide of this element was noted to be tinged brown.

Later workers had difficulty in observing the minor colorless "erbia", but the soluble pink fraction was impossible to miss. Arguments went back and forth as to whether erbia even existed. In the confusion, the original names got reversed, and the exchange of names stuck, so that the pink fraction referred eventually to the solution containing erbium (which in solution, is pink). It is now thought that workers using double sodium or potassium sulfates to remove ceria from yttria inadvertently lost the terbium into the ceria-containing precipitate. What is now known as terbium was only about 1% of the original yttria, but that was sufficient to impart a yellowish color to the yttrium oxide. Thus, terbium was a minor component in the original fraction containing it, where it was dominated by its immediate neighbors, gadolinium and dysprosium.

Thereafter, whenever other rare earths were teased apart from this mixture, whichever fraction gave the brown oxide retained the terbium name, until at last, the brown oxide of terbium was obtained in pure form. The 19th century investigators did not have the benefit of the UV fluorescence technology to observe the brilliant yellow or green Tb(III) fluorescence that would have made terbium easier to identify in solid mixtures or solutions. [33]


Xenotime Xenotim mineralogisches museum bonn.jpg

Terbium is contained along with other rare earth elements in many minerals, including monazite ((Ce,La,Th,Nd,Y)PO4 with up to 0.03% terbium), xenotime (YPO4) and euxenite ((Y,Ca,Er,La,Ce,U,Th)(Nb,Ta,Ti)2O6 with 1% or more terbium). The crust abundance of terbium is estimated as 1.2 mg/kg. [23] No terbium-dominant mineral has yet been found. [38]

Currently, the richest commercial sources of terbium are the ion-adsorption clays 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. [8]

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". [39]


Crushed terbium-containing minerals are treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized with caustic soda to pH 3–4. Thorium precipitates out of solution as hydroxide and is removed. After that the solution is treated with ammonium oxalate to convert rare earths into their insoluble oxalates. The oxalates are decomposed to oxides by heating. The oxides are dissolved in nitric acid that excludes one of the main components, cerium, whose oxide is insoluble in HNO3. Terbium is separated as a double salt with ammonium nitrate by crystallization. [23]

The most efficient separation routine for terbium salt from the rare-earth salt solution is ion exchange. In this process, rare-earth ions are sorbed 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 agents. 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. [23]


Terbium is used as a dopant in calcium fluoride, calcium tungstate, and strontium molybdate, materials that are used in solid-state devices, and as a crystal stabilizer of fuel cells which operate at elevated temperatures, together with ZrO2 . [8]

Terbium is also used in alloys and in the production of electronic devices. As a component of Terfenol-D, terbium is used in actuators, in naval sonar systems, sensors, in the SoundBug device (its first commercial application), 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. [40]

Terbium oxide is used in green phosphors in fluorescent lamps and color TV tubes. Sodium terbium borate is used in solid state devices. The brilliant fluorescence allows terbium to be used as a 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 the trichromatic lighting technology 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. [8]

Terbium is also used to detect endospores, as it acts as an assay of dipicolinic acid based on photoluminescence. [41]

In 2023, terbium compounds were used to create a lattice with one iron (Fe) atom, that was then examined by synchrotron x-ray beam, to examine one atom at sub-atomic levels for the first time. [42]


Handling of terbium, like other lanthanides, should be done with care. Terbium compounds show moderate toxicity, although there is limited data on the specific toxicity of the element. They can act as irritants to the skin and eyes upon contact. Ingestion of terbium compounds should be avoided due to their mildly toxic nature. [43] [44]

In the event of exposure:

For safe handling and storage:

Proper disposal of terbium compounds should be conducted in accordance with local environmental regulations. [47]

See also

Related Research Articles

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Europium is a chemical element; it has symbol Eu and atomic number 63. Europium is a silvery-white metal of the lanthanide series that reacts readily with air to form a dark oxide coating. It is the most chemically reactive, least dense, and softest of the lanthanide elements. It is soft enough to be cut with a knife. Europium was isolated in 1901 and named after the continent of Europe. Europium usually assumes the oxidation state +3, like other members of the lanthanide series, but compounds having oxidation state +2 are 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 rarest of the rare-earth elements on Earth.

<span class="mw-page-title-main">Erbium</span> Chemical element, symbol Er and atomic number 68

Erbium is a chemical element; it has symbol Er and atomic number 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements. It is a lanthanide, a rare-earth element, originally found in the gadolinite mine in Ytterby, Sweden, which is the source of the element's name.

<span class="mw-page-title-main">Gadolinium</span> Chemical element, symbol Gd and atomic number 64

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<span class="mw-page-title-main">Holmium</span> Chemical element, symbol Ho and atomic number 67

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<span class="mw-page-title-main">Lanthanum</span> Chemical element, symbol La and atomic number 57

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<span class="mw-page-title-main">Lutetium</span> Chemical element, symbol Lu and atomic number 71

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<span class="mw-page-title-main">Cerium</span> Chemical element, symbol Ce and atomic number 58

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<span class="mw-page-title-main">Berkelium compounds</span> Chemical compounds

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Scandium compounds are compounds containing the element scandium. The chemistry of scandium is almost completely dominated by the trivalent ion, Sc3+, due to its electron configuration, [Ar] 3d14s2. The radii of M3+ ions in the table below indicate that the chemical properties of scandium ions have more in common with yttrium ions than with aluminium ions. In part because of this similarity, scandium is often classified as a lanthanide-like element.

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<span class="mw-page-title-main">Europium compounds</span> Chemical compounds

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<span class="mw-page-title-main">Terbium compounds</span> Chemical compounds with at least one terbium atom

Terbium compounds are compounds formed by the lanthanide metal terbium (Tb). Terbium generally exhibits the +3 oxidation state in these compounds, such as in TbCl3, Tb(NO3)3 and Tb(CH3COO)3. Compounds with terbium in the +4 oxidation state are also known, such as TbO2 and BaTbF6. Terbium can also form compounds in the 0, +1 and +2 oxidation states.

Cerium compounds are compounds containing the element cerium (Ce), a lanthanide. Cerium exists in two main oxidation states, Ce(III) and Ce(IV). This pair of adjacent oxidation states dominates several aspects of the chemistry of this element. Cerium(IV) aqueous solutions may be prepared by reacting cerium(III) solutions with the strong oxidizing agents peroxodisulfate or bismuthate. The value of E(Ce4+/Ce3+) varies widely depending on conditions due to the relative ease of complexation and hydrolysis with various anions, although +1.72 V is representative. Cerium is the only lanthanide which has important aqueous and coordination chemistry in the +4 oxidation state.

Lutetium compounds are compounds formed by the lanthanide metal lutetium (Lu). In these compounds, lutetium generally exhibits the +3 oxidation state, such as LuCl3, Lu2O3 and Lu2(SO4)3. Aqueous solutions of most lutetium salts are colorless and form white crystalline solids upon drying, with the common exception of the iodide. The soluble salts, such as nitrate, sulfate and acetate form hydrates upon crystallization. The oxide, hydroxide, fluoride, carbonate, phosphate and oxalate are insoluble in water.


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