Yttrium

Meera Senthilingam 

This week, the last of the elements discovered in the small town of Ytterby and its compounds appear to have a multitude of uses. 

Simon Cotton 

Y. This is not a question. Y is the symbol for the element yttrium.

Until about 20 years ago, most scientists had not heard of it, other than vaguely noting where it was in the periodic table, under scandium and above lanthanum. Some people might just have known that it was one of four chemical elements named after the small Swedish town of Ytterby, along with ytterbium, erbium and terbium. 

Then in 1986 two scientists working at IBM in Zurich, Georg Bednorz and Karl Müller, found that lanthanum barium copper oxide became superconducting at what was then almost a record high temperature, 35 degrees above absolute zero. In other words, below minus 238°C the compound's electrical resistance disappeared. 

Bednorz and Müller won the Nobel prize for physics in 1987 for this discovery. Prompting other scientists to dust off their periodic tables, and try switching the lanthanum portion for other similar metals. Two American professors, Maw-Kuen Wu and Paul Chu, together with their research groups at the University's of Alabama and Houston, studied yttrium barium copper oxide. It has the formula YBa₂Cu₃O₇ and is often called YBCO for short. They found that it became superconducting 95 degrees above absolute zero (-178°C).

This may not seem much of a temperature difference, but it meant that YBCO could be kept in the superconducting state using liquid nitrogen, rather than the much more expensive liquid helium. This has inspired lots more studies over the past 20 years. The ultimate objective, the Holy Grail, is to find a material that would superconduct at room temperature, but no one has got there yet. 

There are many possible applications for YBCO; for example MRI scanners could be made to operate more cheaply at a higher temperature using liquid nitrogen coolant. At present, though, there are technical problems preventing these commercial applications. One is that in order to superconduct at 95K, the YBCO has to be slightly oxygen-deficient, to have just a bit less than the seven oxygen atoms per yttrium atom. The exact amount is crucial, and tricky to achieve. 

Other problems include making the YBCO in the right state; a lot of research is going into making thin films of it and finding a way of making it into a continuous wire, rather than just an assembly of crystals packed together that are unable to conduct decent currents. Investigators are looking into depositing YBCO on top of flexible metal wires, and research into this continues. 

Apart from this, there are lots of everyday applications for yttrium compounds In its compounds yttrium is always present as the yttrium three plus ion, which means that it is colourless and has no unpaired electrons; therefore it does not have any interesting magnetic or spectroscopic properties of its own. The up side of this is that yttrium compounds make very good host materials for other lanthanides. 

The most familiar application lies in the red phosphor in cathode ray tubes, as used in traditional colour TV sets. This is made of yttrium oxysulphide, Y₂O₂S containing a small amount of trivalent europium ions. Similarly, yttrium hosts are often used to accommodate terbium ions, which are green phosphors. Such materials are used in the 'cool white' fluorescent lamps. 

Yttrium aluminium garnet, also known as YAG, is a very important synthetic mineral. It is used to make hard, artificial diamonds, which sparkle just like the real ones. What is more, by introducing small quantities of lanthanide ions, materials with a range of useful properties can be made. Introduce a small amount of cerium for example, and you have a good yellow phosphor. Or add 1 % of neodymium to YAG and you get the most widely used solid-state laser material. And erbium gives you an infrared laser. 

Yttrium also finds use in fuel cells for powering cars and buses, computers and digital phones and, potentially, buildings. A small amount of yttrium oxide is added to zirconium oxide to make what is known as yttria-stabilized zirconia (also called YSZ). That has the unusual property of conducting oxide ions, making it very useful in these fuel cells. YSZ is also used to make the lambda sensors fitted to the exhaust sytem of your car. These monitor the amount of oxygen in the exhaust gases and sends feedback to give the best air-fuel mixture into the engine. 

So, that is yttrium for you. Colourless, unspectacular, but undoubtedly fulfilling a lot of important supporting roles. 

Meera Senthilingam 

And so the Oscar for best supporting role goes to, you guessed it, yttrium. That was Uppingham School's Simon Cotton with the multiple roles and uses of yttrium. Now next week we've got an element that could take us into another dimension. 

Hayley Birch 

In 1949, Milton Smith published a short work of fiction that he entitled The mystery of element 117. The real element 117 is yet to be discovered – it's a blank space in the periodic table just below the halogens. Smith's 117, however, was a strange material that could be used to open a window to another dimension. He called it a magnetic monopole substance – one that instead of having poles, plural, like an ordinary magnet, had a pole. Singular. Now, whilst no reputable scientist would argue that a magnetic monopole could open an inter-dimensional portal, its existence isn't outside the realms of possibility and if recent reports are anything to go by, it could depend on an otherwise mundane metallic element that you can find skulking around near the bottom of the periodic table: holmium. 

Meera Senthilingam 

And Hayley Birch will be revealing the truth about such mythical monopoles in next week's Chemistry in its element. Until then, I'm Meera Senthilingam and thank you for listening.