Quasicrystals: A Nobel Story

The announcements have all come in for the Nobel Prizes. It is the highest honour for a scientist. So who won the 2011 Chemistry Prize, in this International Year of Chemistry? Why Dr. Dan Shechtman, a professor of materials science at Technion-Israel Institute of Technology.

Shechtman's work concentrated on crystallinity, but what made his work so interesting, is that he discovered "quasicrystals", a concept previously held to be impossible. His work was met with a lot of criticism and skepticism. His results were suggested to be artifacts, or misinterpretations of microscopy results. His colleagues would hand him textbooks to study, pointing out that these books would clearly show his results were impossible. Overtime, these results were observed by other scientists, and the intense debate began to swing in Shectman's favour.

So what are these interesting and controversial materials Shechtman discovered? Quasicrystals. In crystallography, a crystal is a material in which the atoms are structured in a particular geometric pattern that repeats itself in three dimensional space. These repetitions are at fixed intervals. This means that there are clear definitions of what is allowed symmetry in the crystals, and the 5 and 10-fold rotational symmetry that Dr. Shechtman observed in his materials is certainly NOT allowed by conventional crystallography. In conventional crystallography, crystals may display rotational symmetries of 2, 3, 4 and 6. The reason that 5 fold periodicity is not allowed is because it cannot be exhibited by the crystal as a whole. While a single pentagon many have 5-fold symmetry, an array of pentagons will lack this symmetry. The previously held definitions of crystallinity included periodicity and yet Shechtman's crystals did not have this periodicity. Moreover, these crystals, that lacked the periodicity, were still ordered crystals. The result of Shechtman's work was a redefinition of what it means to be "crystalline" and the introduction of the concept of "quasicrystals".  

To better visualise this concept of periodicity and ordered structure take a look at the picture on the left. Taking a look at it we can agree that there is structure to the pattern, and it does follow mathematical rules, but the pattern is not regular. You cannot fold any part of this image onto itself. The pattern simply doesn't repeat. 

I think one of the most important lessons that we can take from Dan Shechtman is the importance in standing by your data. Too often we as scientists get biased by what we think "should" happen, or what we want to see happen. It becomes easy to shut down new possibilities and new ideas that can change our perceptions and give us a better understanding of the world. After all, is that not our goal in science? Shechtman stood by his data, ensured that his experiments were meticulously done, and did not capitulate to scientific peer pressure. He was able to win ultimate vindication in the form of a Nobel Prize. Congratulations Dr. Shetchman, your story is most inspirational to this chemist, and I hope to many others: scientist and non-scientist alike.

References:

Chemical and Engineering News, October 10th, 2011

West, A. R. Basic Solid State Chemistry 2nd Ed. 1999 John Wiley and Sons Inc. West Sussex, England.