Summary
The central thesis of Dan Shechtman's "Quasicrystals: A New Class of Ordered Structures" is that materials with five-fold symmetry, previously thought impossible under the rules of crystallography, represent a distinct and valid class of ordered solids. Shechtman challenges the prevailing understanding of crystalline order by presenting experimental evidence and theoretical reasoning for structures that possess long-range orientational order but lack translational periodicity.
The book details the discovery and characterization of these quasicrystals, explaining their unique atomic arrangements which violate traditional crystallographic rules. Readers gain an understanding of how quasicrystals are identified through diffraction patterns, their unusual mechanical and electronic properties, and the implications of their existence for materials science and condensed matter physics. The takeaway is a fundamental shift in the definition of order in solids.
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Key concepts
- Quasicrystals — Ordered solid materials possessing long-range orientational order but lacking translational periodicity.
- Five-fold symmetry — A rotational symmetry axis where the pattern repeats every 72 degrees, impossible in traditional crystals.
- Diffraction pattern — The pattern of scattered waves or particles used to determine the atomic structure of a material, which exhibits unique features for quasicrystals.
- Crystallographic restrictions — Rules governing the possible symmetries and arrangements of atoms in crystalline solids, which quasicrystals defy.