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Module-03-01-Crystalography.pdf

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RSET, 2011-12 Crystallography Engineering Physics Crystallography 10.04.2012 1 RSET, 2011-12 Crystallography Engineering Physics 0. Introduction ã Crystallography – Branch of solid state physics dealing with the structure of crystalline solids ã Tools of crystal analysis: X-ray, electron beam ã Properties of solids depend on their crystal structure – E.g. Elasticity, electrical conductivity, magnetism – Classification of solids ã Crystalline solids – Solids with atoms/molecules/groups
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  RSET, 2011-12Engineering Physics Crystallography 10.04.20121 Crystallography  RSET, 2011-12Engineering Physics Crystallography 10.04.20122 0. Introduction ã Crystallography  – Branch of solid state physics dealing with the structure of crystalline solids ã Tools of crystal analysis: X-ray, electron beam ã Properties of solids depend on their crystal structure  – E.g. Elasticity, electrical conductivity, magnetism  – Classification of solids ã Crystalline solids  – Solids with atoms/molecules/groups arranged in a regular fashion such that their positions are exactly periodic  – E.g. NaCl ã Polycrystalline solids  –Composed of many microscopic crystals, called crystallites“ or grains“ – Solids with the periodicity of spiecies interupted at grain boundaries»Grain: Region within which particular periodicity exists  – E.g.: Metals, Ceramics ã  Amorphous solids  – Solids with atoms distributed irregularly or randomly  – E.g. Glass  RSET, 2011-12Engineering Physics Crystallography 10.04.20123 1. Crystal Structure: Space lattice ã Crystal structure = Space lattice + basis  – Space Lattice ã It is the geometry of a set of points in space  – Space lattice represents an array of points in space such that the environment about each point is the same ã Mathematical representation  – Using basic vectors and their translation or parallel displacement  – Position vector of any point P in a space lattice can be represented as sum of integral multiples of basic vectors »2D: »3D: », and are non-collinear vectors or basic vectors of the lattice»Lattice has translational symmetry (non-variability under displacement) specified by the lattice vectors »Crystal looks the same when viewed from any of lattice points bnanT   21 cnbnanT    321 a  b  c  a  b  pT2D Lattice  RSET, 2011-12Engineering Physics Crystallography 10.04.20124 2. Crystal Structure: Basis  – Basis ã The atom, ions, or group which constitute the geometrical pattern of a crystal lattice ã It may be monoatomic (e.g. Al, Ba), diatomic (e.g. NaCl, KCl) or triatomic (e.g. CaF 2 ), etc. ã Basis is identical in composition, arrangement and orientation  – Crystal structure = Space lattice + Basis Basis with 3 atoms

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Jul 23, 2017
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