What is Terbium?
Terbium (symbol Tb) is element 65 on the periodic table, a lanthanide in period 6. A green-phosphor rare earth that also changes shape in a magnetic field. At room temperature it is a solid.
Structure
Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.
Measured values
Every bar shows where terbium sits among all 118 elements for that property.
Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.
Size, to scale
Radius 176 pm — that is 0.176 nm, so about 2841 million of them side by side would span a millimetre.
Thermal range
Terbium is liquid over a 1874 K window, from 1629 K to 3503 K.
The story
A green-phosphor rare earth that also changes shape in a magnetic field.
Discovered by: Carl Gustaf Mosander in Stockholm, Sweden (1843)
Named after: Ytterby, Sweden - the village that gave its name to four different elements
Terbium's discovery represents one of the most challenging achievements in 19th-century analytical chemistry. Carl Gustaf Mosander, working at the Karolinska Institute in Stockholm, began investigating the mineral gadolinite from Ytterby quarry in 1843. This same quarry had already yielded yttrium and erbium, but Mosander suspected additional elements remained hidden.
Using primitive spectroscopic techniques and chemical precipitation methods, Mosander painstakingly separated what he initially called "erbia" into three distinct components. The process required hundreds of crystallization steps and took nearly two years to complete. He identified the yellow fraction as containing a new element, which he named terbium after the village of Ytterby.
Mosander's discovery faced skepticism from the international scientific community. The chemical properties of terbium were so similar to other rare earths that many scientists questioned whether it was truly a distinct element. It wasn't until 1886 that Jean Charles Galissard de Marignac provided definitive spectroscopic proof of terbium's elemental status.
The village of Ytterby holds the unique distinction of being the source of four element names: yttrium, terbium, erbium, and ytterbium. This small Swedish quarry has contributed more element names than any other location on Earth, making it a pilgrimage site for chemistry enthusiasts worldwide.
Today we know that Mosander's original "terbium" sample contained multiple elements. Pure metallic terbium wasn't isolated until 1905 when French chemist Henri Moissan used electrolysis techniques. The characteristic brilliant green fluorescence that defines terbium compounds wasn't fully understood until quantum mechanics explained electronic transitions in lanthanide ions.
Terbium's atomic number (65) places it exactly in the middle of the lanthanide series, giving it unique magnetic and optical properties that were completely unknown to its 19th-century discoverers but now drive billion-dollar industries.
Applications
Terbium stands as one of the most valuable rare earth elements, commanding premium prices due to its extraordinary magnetic and optical properties. In the digital age, terbium has become absolutely critical for data storage technologies, where its magneto-optical properties enable significant advances in computer memory systems.
Terbium-based magneto-optical storage materials have revolutionized digital storage capacity, increasing storage density by 10-15 times compared to conventional systems. These materials form the backbone of next-generation optical storage devices, where terbium's unique ability to change magnetic orientation under laser light creates ultra-high-density data storage solutions.
In trichromatic fluorescent lamps (energy-saving bulbs), terbium serves as a critical phosphor activator, producing brilliant green emissions at 544 nm wavelength. Combined with europium (red) and cerium (blue), terbium creates the perfect white light spectrum while consuming 75% less energy than incandescent bulbs. Modern LED phosphors increasingly rely on terbium compounds for superior color rendering.
Terbium additions to neodymium-iron-boron magnets dramatically enhance their temperature stability and coercivity. Even small amounts (2-5%) of terbium can increase operating temperatures from 80°C to over 200°C, making these magnets essential for electric vehicle motors, wind turbine generators, and aerospace applications where extreme performance is demanded.
Terbium's exceptional magnetic moment makes it invaluable in magnetostrictive alloys used in sonar systems, actuators, and ultra-precise positioning devices. Terfenol-D (terbium-iron-dysprosium alloy) exhibits the largest room-temperature magnetostriction of any known material, enabling applications in underwater acoustics and vibration control systems.
Terbium isotopes serve as contrast agents in medical imaging, while terbium-activated phosphors in X-ray intensifying screens improve image quality while reducing patient radiation exposure. Advanced terbium compounds are being developed for targeted cancer therapies and diagnostic imaging agents.
Despite being one of the most expensive rare earth elements ($800-2000/kg), terbium's exceptional properties make it economically viable for high-value applications. Its scarcity drives innovation in recycling technologies and alternative material research.
Emerging applications include quantum computing components, advanced photonic devices, and next-generation solid-state lighting. Scientists are exploring terbium-based single-molecule magnets for ultra-high-density data storage and quantum information processing.
Where it comes from
1.2 mg/kg of Earth's crust · more abundant than 51% of elements
Terbium represents one of the least abundant rare earth elements in Earth's crust, with an average concentration of only 1.2 parts per million. This extreme scarcity, combined with complex extraction processes, makes terbium one of the most valuable rare earth commodities.
China (85% of global production): Bayan Obo mine in Inner Mongolia produces most commercial terbium. Southern China's ion-adsorption clay deposits in Jiangxi and Guangdong provinces are particularly rich in heavy rare earths including terbium.
Australia: Mount Weld deposit contains significant terbium reserves within its bastnäsite ore body. Lynas Corporation processes this ore at their Malaysian facility.
United States: Mountain Pass mine in California and Bear Lodge project in Wyoming contain terbium-bearing bastnäsite deposits.
Terbium extraction requires sophisticated multi-stage separation processes due to the chemical similarity of lanthanides. Ion-exchange chromatography and solvent extraction using specific chelating agents can separate terbium from other rare earths. The final purification often requires hundreds of separation stages to achieve 99.9% purity.
Given terbium's high value and scarcity, recycling from permanent magnets and phosphors is increasingly important. Advanced hydrometallurgical processes can recover terbium from end-of-life products, though current recycling rates remain below 5% globally.
Handling
Terbium metal and its compounds present moderate safety risks requiring standard laboratory precautions. While not highly toxic, proper handling procedures must be followed to prevent exposure and ensure safe laboratory practices.
Fire Risk: Terbium metal powder is pyrophoric and may ignite spontaneously in air. Store under inert atmosphere (argon or nitrogen) and keep away from oxidizing agents.
Dust Inhalation: Terbium oxide dust may cause respiratory irritation. Work in well-ventilated areas or use fume hoods when handling powdered compounds.
Store terbium compounds in tightly sealed containers in cool, dry conditions. Metal powders require inert atmosphere storage to prevent oxidation. Keep away from strong acids, bases, and oxidizing materials.
Terbium-containing waste must be collected separately for recycling due to its high value and scarcity. Follow institutional waste disposal procedures for rare earth materials.
Quick answers
Terbium (symbol Tb) is element 65 on the periodic table, a lanthanide in period 6. A green-phosphor rare earth that also changes shape in a magnetic field. At room temperature it is a solid.
[Xe] 4f⁹ 6s², giving 6 occupied shells holding 2, 8, 18, 27, 8, 2 electrons respectively.Terbium melts at 1629 K (1355.9 °C) and boils at 3503 K (3229.9 °C).
The standard atomic weight of Terbium is 158.925 u. That is a weighted average across its naturally occurring isotopes, which is why it is rarely a whole number.
Terbium has a density of 8.23 g/cm³. Water is 1.0 g/cm³, so a block of terbium is about 8.2× heavier.
Terbium has a Pauling electronegativity of 1.2. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). A value this low means it readily gives its outer electrons away, forming positive ions.
Terbium was discovered in 1843 by Carl Gustav Mosander. It is named after ytterby, Sweden.
Terbium makes up about 1.2 mg/kg of the Earth's crust — uncommon, but not rare.