Terbium
Atomic Data
| Atomic Number | 65 |
| Symbol | Tb |
| Atomic Weight | 158.93 u |
| Density (STP) | 8.23 g/cm³ |
| Melting Point | 1355.85 °C (1629 K) |
| Boiling Point | 3229.85 °C (3503 K) |
| Electronegativity | 1.2 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f9 5s2 5p6 6s2 |
| Oxidation States | +3, +4 |
| Phase at STP | Solid |
| Category | Lanthanoid |
| Period / Group | 6 / None |
| CAS Number | 7440-27-9 |
Electron Configuration
[Xe] 4f9 6s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 9 | 55 |
| O | 5 | 5s | 2 | 57 |
| O | 5 | 5p | 6 | 63 |
| P | 6 | 6s | 2 | 65 |
| Total | 65 | 65 | ||
Isotopes of Terbium
Terbium is monoisotopic: ¹⁵⁹Tb is its only naturally occurring stable isotope, accounting for 100% of all natural Terbium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Terbium-159 | ¹⁵⁹Tb | 65 | 94 | 100 | Stable |
Abundance & Occurrence
Terbium is present in Earth's crust at approximately 1.2 ppm by mass and at approximately 0.05 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Dust and fume inhalation: Terbium metal dust and terbium oxide are respiratory irritants; use appropriate ventilation and respiratory protection when machining, grinding, or handling fine powders.
- Fire hazard: Terbium metal powder is flammable; use Class D extinguishing agents for metal fires.
- General toxicity: Terbium has low acute systemic toxicity; it is not classified as a carcinogen or reproductive toxicant; standard lanthanide handling precautions are appropriate.
- Storage: Store terbium in sealed containers under inert gas; keep away from strong oxidising agents and moisture to prevent unnecessary oxidation.
Terbium in the Real World
Real-World Uses
- Green phosphors in fluorescent and LED lighting: Terbium(III)-activated lanthanum phosphate (LaPO₄:Ce,Tb) and cerium magnesium aluminate are the standard green phosphors in tri-colour fluorescent lamps, providing the green primary in white-light systems with high colour rendering index.
- Magnetostrictive actuators and sonar: Terfenol-D (Tb₀.₃Dy₀.₇Fe₂) is a giant-magnetostrictive alloy that changes length by up to 0.2% in a magnetic field; used in sonar transducers, precision actuators, ultrasonic cleaning systems, and active vibration control devices.
- Electric vehicle and wind turbine magnets: Terbium is added to Nd-Fe-B permanent magnets to increase coercivity and thermal stability at the elevated operating temperatures of EV traction motors and direct-drive wind turbine generator magnets.
- Solid-state lighting phosphors: Tb-doped aluminium garnet and related phosphors are used in high-colour-rendering LED phosphor blends for museum and retail lighting where accurate colour reproduction is essential.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is terbium used for?
Terbium is used in green phosphors for fluorescent lamps and displays: terbium-activated lanthanum phosphate (LAP) produces the green component of the trichromatic phosphor blend in white fluorescent lamps. Terbium is also used in the magnetostrictive alloy Terfenol-D (terbium-dysprosium-iron), which changes shape when magnetised and is used in precision actuators, sonar transducers, and vibration dampers.
What is Terfenol-D?
Terfenol-D is an alloy of terbium, dysprosium, and iron (approximately Tb0.3Dy0.7Fe2) that exhibits the largest magnetostriction of any known material at room temperature: it changes length by up to 1,000–2,000 parts per million when placed in a magnetic field. This makes it useful in precision actuators for active noise cancellation, sonar projectors, fuel injectors, and linear motors where large displacements from small devices are needed.
How was terbium discovered?
Terbium was discovered in 1843 by Swedish chemist Carl Gustaf Mosander, who separated it from yttria along with erbium. The impure preparations were confusingly named over the following decades, but terbium as a distinct element was eventually confirmed by spectroscopic analysis. Its name comes from Ytterby, the Swedish village that also gave its name to yttrium, erbium, and ytterbium.
Is terbium critical for energy technology?
Yes, terbium is considered a critical raw material by several governments. Its role in green phosphors (essential for energy-efficient lighting) and in Terfenol-D (used in some sonar and actuator applications) makes it strategically important. Like most rare earths, production is dominated by China. The European Union and United States have both listed terbium among their most critical materials.