Terbium Tb

Discovery

The feldspar quarry at Ytterby, near Stockholm, yielded an astonishing number of rare-earth elements. In 1843 the Swedish chemist Carl Gustaf Mosander showed that yttria (yttrium oxide) from Ytterby minerals was not pure and separated two new oxides from it, which he called erbia and terbia.

Later chemists swapped the two names, causing years of confusion. The usual account is that the substance Mosander first called terbia is today's erbium oxide and vice versa. Truly pure terbium compounds became easy to obtain only after ion-exchange techniques were introduced in the mid-twentieth century.

Origin of the name

Terbium is named after Ytterby, the village that also gave its name to yttrium, ytterbium and erbium. Four elements from one small Swedish place name is a record no other location matches.

Main uses

• Green phosphors: trivalent terbium provides the green component of tri-phosphor fluorescent lamps and was used in colour CRTs and X-ray intensifying screens.
• Magnet additive: adding terbium to neodymium-iron-boron magnets raises their coercivity, so they keep working at the high temperatures found in electric-vehicle motors and wind turbines.
• Magnetostriction: Terfenol-D, an alloy of terbium, dysprosium and iron, changes length noticeably in a magnetic field and is used in sonar, acoustic transducers and precise actuators.
• Magneto-optical storage: terbium alloys formed the recording layers of rewritable magneto-optical discs.

Isotopes

Natural terbium is monoisotopic: all of it is stable terbium-159. Among artificial isotopes, terbium-149, -152, -155 and -161 have attracted attention in nuclear medicine because together they could cover imaging and therapy with a single element, an approach called theranostics.

In everyday life

Terbium lives in the green part of your lighting and displays and in the magnets of EVs and wind turbines. It is scarce in the crust and much of the supply comes from ion-adsorption clay deposits in southern China, so terbium often appears in discussions of critical minerals. Its toxicity is thought to be low, but the metal powder is flammable and rare-earth mining and refining carry significant environmental costs.