Terbium (Tb)

Terbium (symbol Tb) is the chemical element with atomic number 65: a lanthanide (rare earth), solid at 0 °C, with an atomic mass of 158.93 u. Discovered in 1843 (Carl Gustaf Mosander).

Terbium gives off a brilliant green light under ultraviolet, which once lit up cathode-ray tubes and fluorescent lamps. Alloyed with dysprosium and iron, it forms Terfenol-D, a material that changes shape in a magnetic field. It is one of the most expensive and strategic rare earths.

Key facts

Atomic number: 65
Symbol: Tb
French name: Terbium
Atomic mass: 158.93 u
Molar mass: 158.93 g/mol
Family: Lanthanides
Position: period 6, f-block
State at 0 °C: Solid
Melting point: 1,355.9 °C
Boiling point: 3,122.9 °C
Density: 8.23 g/cm³
Electronegativity (Pauling): 1.1
First ionization energy: 566 kJ/mol
Atomic radius: 175 pm
Electron configuration: [Xe] 4f⁹ 6s²
Abundance in Earth's crust: 1.2 ppm (59th most abundant element)
Indicative price: 660 $/kg (order of magnitude)
Radioactive: no
Discovery: 1843, Carl Gustaf Mosander

Origin of the name

From Ytterby, a Swedish village.

What does terbium look like?

A silvery-gray metal soft enough to cut with a knife, fairly stable in air.

Where is terbium found?

About 1 ppm of Earth's crust. It is mined mainly from the ion-adsorption clays of southern China and Myanmar, rich in “heavy” rare earths, and from xenotime.

Natural sources

Xenotime
Ion-adsorption clays
Monazite
Euxenite

How is terbium produced?

The ionic clays are leached with a salt solution that releases the rare earths; terbium is then isolated by solvent extraction and ion exchange and reduced with calcium.

Top producers

China
Myanmar

What is terbium used for?

Green phosphors in fluorescent lamps and screens.
Terfenol-D for sonar, actuators and “surface” speakers.
An additive that makes neodymium magnets heat-resistant.
Fluorescence-based biological detectors.

In everyday life

A fluorescent tube or compact fluorescent bulb
An electric-car motor (doped magnets)
A vibration speaker that makes a window or table “sing”

Role in living things

No known biological role.

Hazards of terbium

Low toxicity; flammable metal dust, as with the other lanthanides.

Cosmic origin

Neutron stars: Created when two neutron stars collide — the “forge” of gold.

History of terbium

Mosander identified it in 1843 in yttria taken from an ore mined near the Swedish village of Ytterby. Chemists later swapped the names “terbia” and “erbia” by mistake, a mix-up that lives on in today's names.

Did you know?

Terfenol-D was developed by the US Navy in the 1970s for sonar.
Terbium fluorescence can be used to detect anthrax spores.
It is one of four elements named after the single village of Ytterby, along with yttrium, erbium and ytterbium.

Isotopes of terbium

Terbium has only one stable isotope, terbium-159. Four of its radioactive isotopes form a promising “toolkit” for diagnosing and treating cancer.

terbium-149: radioactive, half-life 4.12 h. An alpha emitter being studied for targeted radiotherapy.
terbium-152: radioactive, half-life 17.5 h. Being studied for PET medical imaging.
terbium-155: radioactive, half-life 5.32 days. Being studied for medical imaging by scintigraphy (SPECT).
terbium-159: 100% of natural terbium, stable
terbium-161: radioactive, half-life 6.95 days. A promising candidate for internal radiotherapy of tumors.

Related elements

Same family (lanthanides): Lanthanum (La), Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Promethium (Pm), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu).