The Ytterby Elements

About a half hours drive out of Stockholm, Sweden, there’s a tiny nondescript town. During the 18th – 20th centuries there was slightly more life here, with a mine operating out of the town.

Ytterby mine, roughly 1910. Courtesy of Tekniska museet on Flickr

One day in 1787, Carl Arrhenius, an army lieutenant, discovered a strange, unusually heavy black ore in the mine. Over the next 100 years, many different elements where discovered from this one ore, later named gadolinite.

These elements are all “rare earth” elements, which, despite the name, are not particularly rare. Their rarity comes more from the difficulty in separating them from each other. It took many scientists many years of research and arguing to discover them all.

Now the little town of Ytterby is not the first place you’d pick to hold a scientific record. Yet it does, as it’s the origin of the names of not one, but four elements. Of the elements in the original gadolinite ore, yttrium, terbium, erbium, and ytterbium all ended up named after the town.

Yttrium

The first element in Ytterby’s story is yttrium. A Finnish chemist, Johan Gadolin, received a sample of the mysterious black ore from Arrhenius. He isolated an unknown element – which later become known as yttrium.

Yttrium’s claim to fame is a discovery made two centuries later in 1987. Yttrium barium copper oxide, a material containing yttrium, is a superconductor at “high” temperatures. Superconductors are strong magnets at low temperatures, and are used in places like in MRIs in hospitals. It is worth noting that to scientists researching superconductors, -180ºC is a high temperature, although to anyone else on the planet it seems freezing. This is because to reach these temperatures, it needs liquid helium cooling. As liquid helium is both expensive and in short supply, hopefully a material like this will soon replace conventional superconductors in MRIs and scientific instruments.

A superconductor becomes magnetic at low temperatures and floats above another magnet. Courtesy of Trevor Prentice on Flickr

Terbium

Further along the table lives terbium. Another Swedish man called Carl, this time Carl Gustaf Mosander, found two more elements in the black gadolinite. A thoroughly unimaginative guy, he named all three after the mine where they were first found – naming Gadolin’s element yttrium, and the other two terbium and erbium.

Terbium is another rare-earth, and is often used in TV screens to make yellow and green phosphors. It’s also mixed with blue and red phosphors to make white light in LEDs.

Terbium sulfate glowing green under UV light. Terbium green is often used in TV phosphors. Credit Chemical Elements, A Virtual Museum

Terbium is versatile, and can also be used in single molecules that act as tiny bar magnets. Usually magnets need hundreds and thousands of individual atoms or molecules. One of these terbium molecules can instead act as a magnet on its own.

The reason why this is important is due to the device you’re reading this on. The storage in computers and phones is made up of tiny little magnetic areas coded with data. These magnetic bits have gotten smaller and smaller as well as faster with time, as computers have gone from filling an entire room to fitting in your pocket. We are now reaching the limit of how small we can make these magnets, but imagine if single molecules could be used instead! With terbium, the dream of minuscule computers may come true.

Erbium

Now erbium is just confusing! The name, as you may have noticed, is very close to that of terbium. This led to some mishaps when the two where first discovered.

Out of the black gadolinite came different coloured element oxides. The original “erbium” was the yellowish coloured stuff, while “terbium” the bright pink stuff. These two were simple enough to separate from the white yttrium. However, when they were discovered people weren’t convinced that they were two separate elements, and by the time they sorted it out, the original names were switched!

These days, erbium refers to the element whose salts are a beautiful rose-pink. If you buy a pair of rose-coloured glasses, chances are there’s erbium!

Small amounts of erbium are also used with yttrium in Er:YAG lasers. They’re useful because the light from these lasers doesn’t travel through the human body. They are therefore useful for dermatology and dentistry, where only the skin or surface of a tooth needs to be treated.

A rare earth (neodymium and yttrium Nd:YAG) laser. Similar lasers are made with erbium or ytterbium and yttrium. Courtesy of Ben Williams on Flickr

Ytterbium

Finally, we have ytterbium. Ytterbium was discovered a lot later than the other three elements, from a sample of erbium by a Swiss chemist Jean Charles Galissard de Marignac. Just like Mosander, he had little imagination, and decided again to name the element after the town.

Ytterbium is also used like erbium in yttrium-based Yb:YAG lasers. Its most interesting use though is in atomic clocks.

Atomic clocks use a vibrating atom to keep time. The ytterbium clock is even more accurate than the caesium atomic clock currently used to define the second. This improved accuracy means that super super fast things in earth sciences and astronomy can be measured.

The Ytterby elements in the lab. Author’s own

Countless other applications of these Ytterby elements exist, and they’re the focus of a lot of research. Any dedicated rare-earth chemist will eventually make the trip to Ytterby to visit the birthplace of these versatile elements.

However, the story doesn’t end with these four. From gadolinite and the mine in Ytterby, 6 other rare-earth elements were discovered:

Scandium: named after Scandinavia

Gadolinium: named after Johan Gadolin

Dysprosium: from the Greek “hard to find”

Holmium: named after Stockholm county, where Ytterby is found

Thulium: after “Thulia”, a Greek name for Scandinavia

Lutetium: from the Latin name for Paris (where the mineral sample was analysed)

You can see the town yourself on Google maps:

For more element stories, see Nature Chemistry’s “In Your Element” series