A type of crystalline phase with Aperiodic order

In April 1982, while on sabbatical at the National Bureau of Standards in Washington, DC, Dan Shechtman from the Technion at Haifa made a pro- found discovery, for which he was awarded the Wolf Prize in Physics in 1999 and the Nobel Prize in Chemistry in 2011. When inspecting various samples of a rapidly solidified Al Mn alloy with an electron microscope in diffraction mode, he noticed a phase that showed clear and sharp Bragg reflexes to- gether with a rather perfect icosahedral symmetry, similar to the one shown in Figure 1.1. While a Bragg spectrum is a typical fingerprint of a crystal, fivefold or icosahedral symmetry is incompatible with the latter. He con- cluded that this phase must possess long-range order (to explain the Bragg reflexes) without being a perfect crystal (to be able to accommodate the un- usual symmetry). It took Shechtman two years to convince colleagues until the result was finally published in Metallic Phase with Long-Range Orientational Order and No Translational Symmetry. Even after the paper appeared in print, prominent scientists (including Nobel Laureate Linus Pauling) ex- pressed their scepticism, though they found themselves in a rapidly shrinking minority as other phases with similar properties were discovered.

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