During his sabbatical leave in the U.S., an Israeli scientist, the 41-year-old Dan Shechtman observed a crystal of alloy of aluminium with manganese under an electron microscope. Suddenly, he discerned something he could not believe – a structure that according to the then state of knowledge could not exist. He saw a circle of concentric circles, each of which consisted of ten dots. And even though he himself thought it to be impossible, he stated that they must be crystals having five-axis symmetry, later named quasicrystals. They were characterised by regularly spaced atoms whose order, however, is never repeated, i.e. were aperiodic. Nevertheless, according to current knowledge, all crystals were built in an orderly, periodic way.
One against all
‘This is what was proclaimed by the classical crystallography. It seemed that everything is clear here,’ says Professor Janusz Wolny from the Department of Condensed Matter Physics, AGH University of Science and Technology in Kraków, who personally knows the Nobel Prize winner. ‘Shechtman destroyed the paradigm that had reigned for 300 years on periodic structure of crystals. This construction was related to the existence of the symmetry of two, three, four and six axes. Until 1982, everybody had been convinced that there was no such thing as five-axis symmetry, and this was exactly what Shechtman recognised in the studied crystals. Not only was he lucky that he stumbled across them, but he also was brave enough to begin to study them. He met with rejection of his discovery very fast – his boss, the famous crystallographer John W. Cahn did not believe him (however in 1984, they wrote an article on that together).
Soon after the discovery, Shechtman wanted to publish his findings. However, the reviews were negative, and the Israeli was not taken seriously by the scientific community, which accused him of overly developed imagination. ‘He should read the manual again,’ some of them mocked. Others argued that what he saw under the electron microscope were “twins” as interconnected crystals are known in crystallography.
His main opponent was the respected twice Nobel Prize winner (in chemistry and peace) Linus Pauling. He claimed that Shechtman’s arguments are uninteresting, and his words have gone down in history: “There is no such thing as quasicrystals, only quasi-scientists”.
It was only in 1984, two and a half years after the discovery, that “Physical Review Letters” published the famous article by Shechtman, Blech, Gratias and Cahn entitled “Metallic phase with long-range orientational order and no translational symmetry”. Subsequent experiments confirmed Shechtman’s discovery and in 1991 the International Union of Crystallography took account of the recent discoveries and changed the definition of a crystal.
Artists knew it earlier
When Shechtman stated in 1982 that quasicrystals existed, Krzysztof Woźniak – today, the crystallochemistry professor at the Department of Chemistry of the Warsaw University – was still a student. A few years later, he went on a scholarship to Cambridge and Shechtman was already mentioned there as a future candidate for the Nobel Prize. ‘Shechtman’s discovery that crystals do not have to be characterised by periodicity was a breakthrough because it made us realise that there is a matter very differently organised than everyone had thought. The mathematical theory that attempts to describe this phenomenon in terms of science has opened the way for a multi dimensional crystallography, based on more than three dimensions,’ comments Professor Krzysztof Wozniak.
‘This year’s Nobel Prizes in chemistry and physics are interesting because they have been granted for intellectual achievements that do not necessarily have far-reaching practical consequences. Of course, aluminium alloys with manganese or nickel are used in industry, but these are not spectacular applications and it wasn’t them what decided about awarding the prize,’ adds Professor Woźniak. Shechtman’s discovery is important for crystallography, solid state physics, materials science and geology. Quasicrystals are used, among others, to coat pans and in diesel engines.
And how do the quasicrystals look like? In the two-dimensional version, such crystals were already formed several hundred years ago by the artists of the Arab world, decorating, for example, mausoleums in Bukhara in Uzbekistan and Isfahan in Iran. Although the decoration is regular, the pattern never repeats. Also the Penrose tiling (discovered in 1973) is a non-periodic system, whose structure is the same as in quasicrystals.
And so, is it sometimes worth to question even the most well-established theories? It is. It is good that Dan Shechtman had no doubts about it.