Terbium

Terbium is one of several rare-earth elements found in yttrium oxide. Because these elements come from the same source, they all have strikingly similar names (and qualities)—which can make them tricky to keep straight!

Terbium was first identified in its oxide form by Swedish chemist Carl Gustaf Mosander in 1843. Mosander was exploring yttrium oxide, which Swedish chemist John Gadolin had discovered in 1789. Yttrium oxide contained the element yttrium, but Mosander suspected that the oxide might contain other elements, too. He separated the yttrium oxide into the oxides yttria, erbia, and terbia (which contained the elements yttrium, erbium, and terbium).

Not long after this discovery, the names of terbia and erbia were confused—a mix-up that persisted for several decades. In the end, the elements switched names to the ones we recognize today!

Incidentally, the terbium and erbium that Mosander discovered later yielded other new elements, such as thulium and lutetium, as well.

Terbium is a silvery metal that is malleable (meaning that it can be hammered into shape) and ductile (meaning that it can be stretched without breaking). Terbium is soft enough to be cut with a knife!

Terbium doesn’t have all that many commercial uses, in part because it’s very expensive to produce (a gram of terbium costs four times as much as a gram of platinum!). When exposed to magnetic fields, terbium alloys can lengthen or shorten, which makes them useful in things like speakers, and also, potentially, in motors and pumps.

Like other rare-earth elements, terbium can be used as a component in lasers. It has also been used in lamps and color television tubes. Because terbium oxidizes easily, it’s often used for research.

Terbium oxidizes easily and has a number of oxides, some of which are used in fluorescent lamps, television tubes, and computer screens. Certain terbium compounds emit a bright green color, and these compounds have been used in medicine, making it possible to see whether specific reactions are taking place inside a patient’s body.

TbFe₂-based compounds are magnetorestrictive—that is, they become smaller or larger when exposed to a magnetic field—which makes them useful in electronics.

In nature, you’ll find only one stable (non-radioactive) terbium isotope (terbium-159). In laboratory contexts, scientists have observed some 36 radioisotopes whose half-lives range from 180 years (terbium-158) to much less than one second.

Like other rare-earth elements, most terbium comes from monazite and bastnäsite ores. China is the top producer of these ores, so it’s the top producer of terbium, too. Russia and Malaysia also produce terbium.