1. QUASICRYSTALS Francesca Violich

2. Who discovered them? The Nobel Prize Dan Shechtman • The 2011 Nobel Prize in chemistry went to Dan Shechtman (70), who is a professor of material sciences at Technion-Israel Institute of Technology in Haifa, Israel • “for the discovery of quasicrystals”

3. How the discovery happened: • Scientists believed that crystals in materials all contained repeating patterns. • For example, a square lattice has fourfold symmetry. Rotate it by 90 degrees, and it looks identical. • But a repeating lattice with fivefold symmetry is impossible. • On that morning in 1982, the electrons Dr. Shechtman bounced off his aluminum-manganese alloy formed a pattern that indicated tenfold symmetry. • He wrote in his notebook, “10 Fold???” While a periodic lattice could not produce that pattern, a quasicrystalcould.

6. More on the discovery: • Shechtman's image, however, showed that the atoms in his crystal were packed in a pattern that could not be repeated. • His discovery was extremely controversial. • In the course of defending his findings, he was asked to leave his research group. • However, his battle eventually forced scientists to reconsider their conception of the very nature of matter.

7. Okay, so what are quasicrystals? • A quasiperiodic crystal, or, in short, quasicrystal, is a structure that is ordered but not periodic. • A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry. When you slide/rotate it around, it looks the same a shifted copy will never match exactly with its original

8. aluminum Palladium manganese What is isocosahedral? Atomic model of fivefold icosahedral-Al-Pd-Mnquasicrystal surface

9. In case you’re curious Electron diffraction pattern of an icosahedral Ho-Mg-Zn quasicrystal

10. Types of Quasicrystals In theory, there are two types of quasicrystals. The first type, polygonal (dihedral) quasicrystals, have an axis of eight, ten, or 12-fold local symmetry (octagonal, decagonal, or dodecagonal quasicrystals, respectively) They are periodic along this axis and quasiperiodic in planes normal to it. The second type, icosahedralquasicrystals, are aperiodic in all directions.

12. Quasicrystals have so far had a modest impact in the everyday world.One kind of highly resilient steel, consisting of hard steel quasicrystals embedded within softer steel, is now used in razor blades and thin needles for eye surgery.