Scitech | 2011 Nobel Prizes – Chemistry: crystal clear

Chemistry: crystal clear

Almost 150 years ago Alfred Nobel patented dynamite – a mixture of nitroglycerin and an inert substance (like dirt). This invention amassed him a fortune. Years later, when his brother died, a French newspaper erroneously published Nobel’s own obituary, calling him a “merchant of death.” Worried about his legacy and potentially plagued with guilt, Nobel donated the majority of his estate to the creation of the Nobel Prizes after his death. Each year, the Nobel Prize committee gathers together to choose laureates for physics, chemistry, physiology or medicine, literature, and peace. Astute readers may wonder why there is no Nobel Prize for math – legend has it that  Nobel never got over the fact that a mathmatician stole away one of his lovers.

 

Some ancient Arabic mosaics are known to feature a distinct pattern. These patterns, although unvarying, never repeat themselves. Their organization follows mathematical rules: the pattern is scaled using the golden ratio, a number approximately equal to 1.618 and commonly used in art and geometry to create aesthetically appealing images. However, the other characteristic of mosaics – the non-repeating patterns – aren’t a phenomenon unique to art. Surprisingly, these macroscopic patterns helped reveal that the microscopic properties of crystals are not as simple as once believed.

On October 5, the Nobel Prize in Chemistry was awarded to Dan Shechtman, an Israeli chemist who discovered quasicrystals. This form of solid crystals contains no translational symmetry – that is, the crystals do not look the same no matter which direction or how far they are shifted. A wallpaper with a repeating pattern is an example of translational symmetry – even if it is slid to the right or left, it will appear the same as before. Before Shechtman’s discovery, crystals were thought to be like wallpaper, arranged in symmetrical, repeating patterns. Yet, when Shechtman examined a rapidly cooled metal alloy under an electron microscope, he found that the crystals that formed did not contain repeating units. Instead, they resembled the patterns found in ancient mosaics.

Shechtman’s discovery broke the most fundamental law of crystal structure, which assumes that only two, three, four, and sixfold symmetries were possible. Pentagonal or fivefold symmetry, was considered to be impossible due to unachievable spacing between atoms. Amazingly, the results of Shechtman’s research showed fivefold symmetry in the crystal structure. The fact that Shechtman’s fivefold pattern didn’t repeat itself caused other scientists to disregard his results. His results were so controversial that he was ridiculed by the scientific community and was asked to leave his research group shortly after he made his discovery in 1982.

However, this didn’t stop Schectman. Along with several colleagues, he refined and published their findings in 1984. Shortly thereafter, other scientists discovered other seemingly impossible crystal structures, such as structures containing eight and twelvefold symmetry, giving more legitimacy to Shechtman’s results. As his discovery became more widely accepted, a paradigm shift occurred in the field of crystallography. The very definition of a crystal was altered: it could no longer be said that all crystals contain a regular, repeating pattern of atoms.

Many types of quasicrystals have now been synthesized, and have recently been found occurring in nature in a mineral sample from Russia. Due to the nature of their structure, quasicrystals are extra hard and are poor conductors of both heat and electricity. Although quasicrystals have no practical applications yet, quasicrystal fyring pans may soon be in use, as quasicrystals have a non-stick surface. They may also be useful in diesel engines and LED bulbs to control the flow of heat.


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