Terbium Facts – Element Tb or Number 65

Terbium Facts
Terbium is a silvery-white metal with symbol Tb and atomic number 65 that finds use in green phosphors.

Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable, ductile, and soft enough to be cut with a knife. Terbium is a member of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table.

Discovery and Naming

Terbium was discovered in 1843 by the Swedish chemist Carl Gustaf Mosander at the Karolinska Institute in Stockholm. He detected it as an impurity in yttrium oxide, Y2O3. Mosander actually discovered terbium, erbium, and yttrium, naming all three after the village of Ytterby in Sweden, where the first rare earth minerals were discovered.

Physical Properties

In its pure form, terbium is a fairly electropositive metal that is solid under standard conditions. It is relatively stable in air, but water oxidizes it and it is soluble in diluted acids. Terbium displays a range of magnetic properties. It is ferromagnetic below 219K, antiferromagnetic between 219 and 230K, and paramagnetic above 230K.

Natural and Radioactive Isotopes

Natural terbium consists of one stable isotope: terbium-159. There are 36 synthetic radioisotopes, ranging from terbium-135 to terbium-171. The most stable of these is Tb-158, which has a half-life of 180 years.

Electron Levels of a Terbium Atom

Abundance and Sources

Terbium is not found free in nature but is extracted from minerals such as xenotime, euxenite, and monazite. It is relatively scarce, with an abundance in the Earth’s crust estimated to be about 1.2 mg/kg. The primary source of the element consists of clay from southern China. A newer supply occurs off the coast of Japan.


The extraction and purification of terbium are complex processes involving solvent extraction and ion exchange techniques. This process usually starts with the crushing and milling of monazite ore, followed by ion exchange to separate the rare earth elements.

Uses of Terbium

The principal use of terbium is as terbium oxide from green phosphors, but it has other application, too:

  • Luminescence: Utilized in green phosphors for color TV tubes and fluorescent lamps and as a component of trichromatic lighting.
  • Electronics: Used in solid-state devices and as a dopant in calcium fluoride, calcium tungstate, and strontium molybdate.
  • Magneto-optical recording: Terbium-iron-cobalt alloys are used in magneto-optical recording disks.
  • Magneto-mechanical devices: The terbium alloy Terfenol-D finds use in sensors, sonar systems, and actuators.
  • Microbiology: An assay based on photoluminescence detects bacterial endospores.

Oxidation States

Terbium primarily exhibits the +3 oxidation state, which is the most stable and common form. The +4 state is rare and typically seen only in a few compounds. However, the element exhibits all oxidation states from 0 to +4.

Biological Role and Health Effects

Terbium has no known biological role in humans or other organisms. It is considered to be of low toxicity, but it should be handled with care to avoid exposure and ingestion. The element and its compounds cause skin and eye irritation.

Table of Key Terbium Facts for Scientists

This table provides essential information for scientists and researchers working with terbium, offering a quick reference to its fundamental properties and characteristics.

Atomic Number65
Atomic Weight158.92535
Groupf-block (Lanthanides)
Electron Configuration[Xe] 4f9 6s2
Electrons Per Shell2, 8, 18, 27, 8, 2
State at Room Temp.Solid
Melting Point1,356°C
Boiling Point3,123°C
Density8.23 g/cm³
Heat of Vaporization391 kJ/mol
Heat of Fusion10.15 kJ/mol
Molar Heat Capacity28.91 J/(mol·K)
Oxidation States0, +1, +2, +3, +4
Ionization Energies1st: 565.8 kJ/mol
Atomic Radius177 pm (empirical)
Covalent Radius194±5 pm
Crystal StructureHexagonal close-packed (hcp)
Thermal Conductivity11.1 W/(m·K)
Electrical Resistivity1.150 µΩ·m (at 20 °C)
Shear Modulus22.1 GPa
Bulk Modulus38.7 GPa
Mohs Hardness~2.5
Magnetic OrderingParamagnetic at 300K

Interesting Terbium Facts

  • Color-Changing Properties: Terbium can exhibit fascinating color-changing properties when combined with other elements or compounds. For example, terbium-doped calcium fluoride changes color under different light sources due to fluorescence.
  • Sound Production: Terbium is a component of “terfenol-D” (an alloy of terbium, iron, and dysprosium). This material exhibits giant magnetostriction, meaning it rapidly changes shape in a magnetic field, making it useful in sonar systems and other sound-producing devices.
  • Nuclear Medicine: Some isotopes of terbium, such as 149Tb and 161Tb, are candidates for positron emission tomography (PET) and cancer treatment through targeted alpha therapy.
  • Superconductivity: Under high pressure, terbium hydride becomes a superconductor. This means it conducts electricity without resistance, giving it potential applications in advanced electronic devices and magnetic resonance imaging (MRI).
  • Role in Green Energy: Terbium is important for improving the efficiency of solid-state devices such as fuel cells.
  • Space Exploration: Terbium finds use in alloys and materials that need to withstand high radiation levels and extreme temperatures.
  • Rare Earth Rarity: Despite being a rare earth element, terbium is more abundant in the Earth’s crust than tin or lead. However, it is rarely exists in concentrated amounts, making extraction challenging.
  • Phosphorescent Properties: Terbium salts are phosphorescent materials. When exposed to light, they absorb photons and then release them slowly, making them valuable in glow-in-the-dark products.
  • Optical Fiber Technology: Telecommunications use terbium-doped optical fibers for amplifying signals in fiber optic cables, enhancing long-distance communication capabilities.


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