Alpha plutonium – a rebel element

What does it look like?

The crystal structure of alpha plutonium, image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/.

The crystal structure of alpha plutonium, image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/.

What is it?

Over the year we’ve introduced the crystal structure of a number of elements. Most of them take up very simple crystal structures, those that you can also form by pouring ping pong balls into a box. Atoms of materials like gold, krypton and even curium pack like this.

We’ve also introduced elements that don’t conform to the ‘simple crystal structure’ rules at room temperature – the elemental rebels so to speak. These are the elements where the atoms are awkward – they need to be *that* bit further away from each other.

The latest of these ‘rebel’ element is plutonium. This element, actually has seven allotropes, with a face centred cubic phase (known as the delta-phase) stable at just above room temperature, 310 K. Below this it forms a crystal structure known as it’s alpha-phase, which is monoclinic, a low symmetry structure that has low thermal conductivity and is quite brittle. Not great for use in reactors.

We’ve actually learnt how to tame the plutonium crystal structure somewhat. Alloy plutonium with a little bit of gallium, aluminium, americium, scandium or cerium and it forms into a gold-like face-centred cubic structure that isn’t brittle and conducts heat much better.

Where did the structure come from?

The structure of alpha plutonium was discovered by Zachariasen, and Ellinger 1963. It’s #9008587 in the Crystallography Open Database.

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A failed campaign – alpha and beta tin

What does it look like?

'White' or beta tin the structure of tin at room temperature Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

‘White’ or beta tin the structure of tin at room temperature Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

'Grey' or alpha tin the structure of tin at temperatures below -40oC Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

‘Grey’ or alpha tin the structure of tin at temperatures below -40oC Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

What is it?

When Napoleon’s armies marched towards Russia in June 1812, they were freshly kitted out with new uniforms, weapons and provisions, full of confidence in their future success in conquering to the East.  Yet later that year, the bedraggled remains of this army limped back to France, heavily defeated.  There were many reasons why Napoleon’s army failed in their conquest, but a quirk of crystal structure can’t have helped.  The uniforms of the Napoleonic army were held together by tin buttons, but in the protracted cold temperatures of the Russian winter these buttons started to crumble.  The reason?  What is often referred to as ‘tin pest’.

 

Tin pest is in fact a change of crystal structure of the tin itself.  When temperatures drop towards -40°C the metallic ‘white tin’, known also as beta-tin – will change to ‘grey tin’ or alpha tin.  The atoms within the alpha tin are co-ordinated, like carbon in diamond, to four other tin atoms making the material brittle.  As the French army strove through the Russian winter and temperatures dropped, so their buttons would have started to crumble. 

Where did the structure come from?

The structures of alpha and beta tin were determined by both structures can be found in the Open Crystallography database # 9008568 and # 9008570

A super cool material – the crystal structure of Krypton.

What does it look like?

Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

What is it?

The first of our requested crystal structures, well nearly…  On twitter we asked ‘What crystal structure would you like to see blogged about’ and our friends @Aus_ScienceWeek asked for Kryptonite.  OK, if we had access to kryptonite (of the green variety) I’m not sure we’d be doing crystallography, we’d be finding other ways to save the world.  But how about the element Krypton, that’s close, right?

Krypton is a noble gas, and so not something we tend to think of as a solid crystalline material.  Like the other noble gases, argon and neon to name a couple, they have full outer shells of electrons, no room to accept any others and none to give away for the formation of bonds with other elements. In fact the first compound with a noble gas wasn’t discovered until 1962.  It’s this full shell that makes the noble gases pretty unreactive; they like to sit on their own being, well, nobel. This unreactivity makes them pretty useful for creating neutral environments to play with other materials. Lots of gloveboxes will be filled with argon, and lightbulbs will often be filled with neon and other noble gas mixtures.

But what if we cool it down?  Krypton will become a liquid at about -153°C but only stays liquid for a very narrow window as it will freeze to a solid at -157°C.  Solid Krypton is an example of a hexagonally close packed solid, the other most efficient way of pack spheres to cubic close packing (the structure that gold takes up).

Where did the structure come from?

This krypton structure is #9012404 in the open crystallography database.

Madam Curie – one of her elements Curium

What does it look like?

The double hexagonal close packed structure of Curium.

The double hexagonal close packed structure of Curium.

What is it?

Today would have been Marie Curie’s 147th Birthday.  It’s also medical physics day in honour of the fact that her discoveries lead to the the way we treat many types of cancer with radiation.

Marie Curie’s accolades are well known, amongst other things she was the first person to win both a chemistry and physics Nobel prize.  We’ve actually already covered the curious crystal structure of one of the elements she discovered, Polonium, so instead today we thought we’d cover the element named after her and her husband, Curium.

Curium was first intentionally synthesised in 1944, using a cyclotron at the University of California.  It’s the heaviest of the actinide elements that you can make milligrams of, anything heavier only exists for long enough for a few atoms at a time to exist.  Curium it thought to form a couple of crystal structures, the one we’ve shown here element structure that we haven’t featured on crystallography 365 yet, a double hexagonally closed packed structure. This means that it forms a layered structure, one repeats (the yellow layer in the picture) and in between that two other types of layer (red and blue) form in between that.

Where did the structure come from?

Nobody has ever really made enough curium to do a diffraction study of it, so the structure has been determined from ab initio theory methods by Milman et al in 2003.  You can read more about how they did this in their paper.

Future Boron: Virtual Synthesis is the Next Phase.

What does it look like:

Two views of  a possible new high pressure allotrope of Boron- B56

Two views of a possible new high pressure allotrope of Boron- B56

What is it?

It’s an allotrope of Boron. Maybe. In a previous C-365 blog episode, we described an allotrope of Boron that was discovered in 1951. And when we say “discovered” we mean “someone found a crystal, measured it and did the crystallography”.

The cubic B56 structure shown above is a high pressure phase described in a recent open access paper. The catch? No one knows if it actually exists or not. The structure is one of a number “hand created” using some plausible hypotheses and then computer modeled using density functional theory to see if it was “stable”. The “in the box” synthesis of computational chemistry is not new, but in another example of how the world has been changed by Moore’s Law, has become a routine part of the chemist’s toolbox. Still, as the old saying goes, a computer can make more mistakes in a day than you can in a lifetime.

Where does the structure come from?

The paper is: Fan et. al., “Phase transitions, mechanical properties and electronic structures of novel boron phases under high-pressure: A first-principles study.” Scientific Reports 4, 6786 doi:10.1038/srep06786

Brimstone (sulfur)

What does it look like?

Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

What is it?

When engulfed in fire and brimstone, have you ever wondered what brimstone actually is? Well in this context it’s referring to sulfur – with all the negative connotations that this yellow, smelly substance has. We’ve already featured one allotropes of sulfur, the S10 rings. But as we explained back then sulfur is probably the element with the most different ways of packing itself in a crystal structure – many have been discovered so far!
Many of the sulfur structures are composed of rings of sulfur atoms – today’s is no exception to this. Instead of rings of 10 sulfur atoms, here we have the more common form rings of 8 atoms.

Where did the structure come from?

This structure we’ve featured today is that of alpha-sulfur, which was first reported by Coppens et al, we obtained the CIF (which is hosted on the Inorganic crystal structure database) through the chemical data service (CDS) links on this page.

Boron – an element to watch for the future

What does it look like?

The arrangement of 12-atom boron clusters in the alpha-tetragonal boron structure.  Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

The arrangement of 12-atom boron clusters in the alpha-tetragonal boron structure. Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

What is it?

It has been a while since we’ve featured an element’s crystal structure on the blog. It’s been said before but we’re continually fascinated that, despite the fact that these crystal structures are made up of just one building block, they can form a whole range of beautiful structures.

Today’s element is no exception to this, boron sits on the top row of the periodic table – it’s the 5th element on the list. One of the features of boron as an element is that it forms clusters with itself. Clusters of 6 atoms, and two arrangement of 12 atoms , and now even a ‘buckyball’ structure.

When you start combining this boron clusters with rare earth elements, then a whole range of interesting properties start to emerge. Many of these materials have been observed to have low thermal conductivity, making them potentially great candidate materials for helping generate thermoelectric power. There’s a wikipedia page that someone has put a lot of crystallographic love into on these materials, in particular scandium and boron complexes.

Where did the structure come from?

We’ve featured one of the first crystal structures of boron, its rare alpha tetragonal allotrope. This was determined in 1951 by Hoard et al, from ‘needle like’ crystals and is reported as a short note in JACS. The structure is #9012288 in the Open Crystallography Database.