17 overheads symmetry illustrations

17 overheads symmetry illustrations - Pointgroups:whywecare

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Point groups: why we care Physical properties Point group of crystal is a subgroup of the symmetry group of any of its physical properties. The symmetry group of any property of a crystal must include the symmetry operations of the point group. Enantiomorphism, chirality: The absence of improper rotations (rotoinversion, rotoreflections). In particular the absence of a center of symmetry 1, mirror plan, m=2, and 4 axis. This means the molecules occur as right or left handed (two forms) Enantiomorphic crystals exhibit optical activity formation about the point group of a crystal may be obtained information about the point group of a crystal may be obtained by the observation of physical effects. any interesting physical properties occur only in non ntrosymmetric Many interesting physical properties occur only in non centrosymmetric crystals ( piezoelectricity , pyroelectricity, optical activity) Optical properties: Refractive index, optical activity, SHG International Tables for Crystallography (2006). Vol. A, Chapter 10.2, pp. 804–808, BY H. KLAPPER AND TH. HAHN 10.2. Point group symmetry and physical properties of crystals
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piezoelectricity Initially unpoled Dipoles unaligned material expansion Domains with
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17 overheads symmetry illustrations - Pointgroups:whywecare

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