Book Notes-Crystallography

Book Notes-Crystallography - Intro Musthavesymmetry...

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Intro Must have symmetry Repetition through a volume or around a point Translational Symmetry Plane Lattices o Center of each spot at intersection of lattice lines is a lattice node o Unit meshes are the 4 shapes that can make up the 5 plane lattices Space Lattices and Unit Cell o Plane lattices layered to make 3D o Unit cell- volume outlined by lattice nodes o Crystal axes-edges of unit cell Bravais Lattices and Crystal Systems o 14 types in 6 groups divided by unit cell shape Point Symmetry How a motif can be repeated around a point Reflection o Monoclinic crystal system only one mirror plane possible (like  human symmetry) o Triclinic-none o Isometric-up to 9 Rotation
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o Noted with A sub #of fold o 1-360, 2-180, 3-120, 4-90, 6-60 o everything has infinite number of 1 fold because it brings it back to  original position Inversion o Any line through origin creates symmetry o Indictated with i Compound Symmetry Operations o Rotoinversion axes- rotation axes with inversion o Symmetry Notation o Ex: i,3A sub2,3m i- center symmetry 3m- 3 mirrored planes 3A sub2- 3 2 fold rotation axes o Hermann- Mauguin: presence of some symmetry implies of others-  more abbreviated Ex: 2/m2/m2/m 3 2 fold axes, each perpendicular to a mirror implies center symmetry 32 Point Groups 2d- mirrors and rotation, inversion only in 3D Steno’s Law
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o Angles b/w crystal faces are consistent Measurement of Crystal Angles o Goniometer- measures crystal angles Determining Crystal System and crystal Class o Center symmetry?- Identify mirror planes- Identify Rotation axes-  Compile combination of symmetry Space Groups ????????????????
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