Superconductivity Observed In Europium Metal Using Diamond Anvil Accessible Pressures.

[NNadir]

Tonight in connection with some other projects on which I am working, I was studying the metallurgy and thermodynamic properties of the element technetium, an artificial element with refractory and strength properties that is, among other things, a remarkable corrosion inhibitor.

Regrettably this valuable element has not enjoyed the appreciation that it should because it has no naturally occurring isotopes and is, in fact, radioactive.

One of the more remarkable properties of technetium is that it is the pure metal with the second highest transition temperature to the superconductive state known, a little under 8 kelvin, or 8 degrees below absolute zero.

Technetium alloys can have even higher transition temperatures than pure technetium. For instance, a technetium titanium alloy is known that has a superconductive state at 11C.

Superconductivity, as I'm sure most readers here know, is the property of a material in which electricity can flow without resistance. If it does this in a circular or cyclic system, an intense and stable magnetic field is generated.

Since helium is decidedly not a renewable resource, all helium released to the atmosphere boils off (eventually) into space, and because superconductivity on which NMR (MRI) and many other technologically important systems depend on access to superconductive systems, all of which are currently immersed in liquid helium, it would be nice to have systems that have superconductivity at the boiling point of hydrogen, about 22 K, that could carry high current densities. (All known superconductors that have transition temperatures higher than 22K are, in fact, ceramics, and regrettably do not allow for high current densities.)

It turns out that among the lanthanide elements, sometimes called the "rare earths" only one pure metal has been known to be superconductive, lanthanum itself, although several relatively high transition alloys of rare earths, as mentioned when discussing technetium.

Actually the property of superconductivity is not merely a function of temperature. It is also a function of pressure.

High pressure science has been explored in recent years by the use of an instrument known as the diamond anvil.

(On another website I wrote a very sarcastic piece about this instrument, mocking a person who worked as an intern at Hanford, and as a result, has declared herself an expert on all things nuclear, including the development of nuclear weapons in Iran. Sigh...

Here's the sarcastic diatribe: http://www.dailykos.com/story/2009/4/1/709780/-The-Diamond-Window.">The Diamond Window.

It's hard to say whether one should laugh or cry when facing bourgeois ignorance, especially inflated bourgeois ignorance, but no one should expect much respect for science these days. I suppose that one strategy would be simply to not acknowledge it, but regrettably unchallenged ignorance can be very pernicious, particularly in these dangerous times.)

Anyway. Using the diamond anvil to achieve very high pressures, europium metal, which is an f element and is close in the periodic table to some important paramagnetic metals like neodymium and samarium, has been observed as having a superconductive state.

A generally accessible article on this matter is available here:

http://www.sciencenews.org/view/generic/id/43960/title/Europium%E2%80%99s_superconductivity_demonstrated

An old element just learned a new trick under pressure. When cooled and squeezed very hard, the soft metallic element europium turns into a superconductor, allowing electrons to flow unfettered by resistance, a study appearing May 13 in Physical Review Letters shows. The results make europium the 53rd of the 92 naturally occurring elements to possess superconductivity, which, if harnessed, could make for more efficient energy transfer.

Europium, a rare earth metal with a silver color, is strongly magnetic at everyday temperatures and pressure. Study coauthor James Schilling of Washington University in St. Louis suspected europium would superconduct if researchers could overcome its magnetism, which disrupts a certain type of electron pairing that superconductivity requires. “Most of the rare earths would be superconducting at ambient pressure, except that they’re magnetic,” Schilling says...

The primary paper was published this year in Phys. Rev. Lett..

Here is the abstract of the paper: http://scitation.aip.org/vsearch/servlet/VerityServlet?KEY=PRLTAO&smode=strresults&sort=rel&maxdisp=25&threshold=0&allprl=1&possible1=Europium&possible1zone=multi&bool1=and&possible2=James+Schilling&possible2zone=author&OUTLOG=NO&articlecategory=apsAllarticles&viewabs=PRLTAO&key=DISPLAY&docID=1&page=1&chapter=0">Phys. Rev. Lett. 102, 197002 (2009) <4 pages>

Here's a brief excerpt from the text of the article:

Bernd Matthias once mused that all nonmagnetic metals might become superconducting, if only they be cooled to a sufficiently low temperature <1>. Of the 92 naturally occurring elements in the periodic table, there are 30 known elemental superconductors at ambient pressure and 22 more that become superconducting under high pressure <2>. An intriguing question is whether the remaining 40 elemental solids become superconducting in some temperature or pressure range. One could, in fact, pose this same question for all solids.

Across the entire lanthanide series, only its first member, La, superconducts at ambient pressure. The reasons for this appear to be twofold: (1) the local-moment magnetism in all lanthanides except La, Yb, and Lu leads to strong pair breaking effects, and (2) as for nonsuperconducting Sc or Y, the relatively weak d character of the conduction electrons for heavy lanthanides like Lu results in an only diminutive pairing interaction. Since compressing the lattice enhances the d-electron concentration, it is not surprising that Sc, Y, and Lu all become superconducting under pressure <3>; indeed, the vast majority of transition metals superconduct.

In contrast, the pressure-induced superconductivity observed for Ce metal above 2 GPa arises from the suppression of its magnetism <4>. The fact that all lanthanides other than La, Ce, and Lu do not superconduct under pressure, in spite of their enhanced d-electron concentration, is a tribute to the stability of their strong local-moment magnetism. At sufficiently high pressures, however, one would anticipate that the lanthanide valence should increase as electrons are successively squeezed out of the 4f shell into the s, p, d-conduction band.

In the quantum mechanical garage, by the way, one can mess with the electronic structure of elements at extreme pressures, in effect squeezing electrons. That's incredibly cool. The quantum mechanic Roald Hoffman, who was awarded the Nobel Prize in chemistry for his interpretation of the quantum mechanical implications of a certain set of organic reactions is now studying high pressure chemical physics. I was privileged to see a recent talk of his on the topic, and the electronic implications kind of blew my mind.

[AlecBGreen]

1. thanks for the info NNadir

:patriot:

[NNadir]

3. My pleasure.

[NNadir]

2. Errata

I wrote this post quickly and made some errors.

One: Tc transition is 8 degrees K above absolute zero, not below. There is no such thing as "below absolute zero."

The transition temperature of Tc/Ti alloys is 11 K, not 11 C. Life would be a lot easier if there were anything that was superconducting at 11 C, which is 284K, the temperature of a cool spring or fall day.

I thank Massacure for pointing out my errors by private email.

[joshcryer]

4. We get into spats ocassionally but that was an awesome post.

Much respect.

[NNadir]

5. Well, I can't say I recall any particular spats - I have so many of them - but in any case

thanks.

I thought it was an interesting case, and couldn't help posting it.

[Occulus]

6. Very cool stuff! It gave me a turn, though, when I read

"8 degrees below absolute zero". I know they meant above, but I was all "whaaaa...?" for a second.

[NNadir]

7. I posted errata.

It's also supposed to say "11K"