lecture_2_chex42

lecture_2_chex42 - Crystal Structure and Defects Crystal...

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Crystal Structure and Defects Crystal Structure and Defects • The goal of this lecture is to review some fundamental concepts from Materials Science necessary to understand and to talk about the properties of the materials we are processing. – Microstructure – Crystal Structure and Crystallography – Crystal Defects
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Microstructure of Materials Microstructure of Materials ¾ Spatial arrangements of atoms play an important role in determining the electrical properties. ¾ Solids are classified into three broad classifications: ¾ Amorphous: no recognizable long range order ¾ Crystalline: Entire solid is made up of atoms in an orderly array ¾ Polycrystalline: Completely ordered in segments Amorphous Polycrystalline Crystalline
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Microstructure of Materials Microstructure of Materials Amorphous Polycrystalline Crystalline
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Crystal Structure Crystal Structure ¾ Crystal structures are regular 3-dimensional patterns of atoms in space ¾ The regularity with which atoms are packed in solids arises from geometrical conditions (i.e., bond angles and lengths) which are imposed by directional bonding and close packing ¾ Most stable arrangement will be the one that 1) Minimizes energy/volume 2) Preserves electrical neutrality 3) Satisfies directionality and discreteness of the covalent bonds 4) Minimizes ion-ion repulsion 5) Packs atoms as closely as possible consistent with (1)-(5)
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Set of all points defined by where u 1 , u 2 , u 3 are integers Description of Crystal Structure: Lattice Description of Crystal Structure: Lattice ¾ A lattice is an infinite three dimensional array of points in which every point has surroundings identical with that of every other point. These are called lattice points . ¾ Example: A 2-D square space lattice: a 1 a 2 3 3 2 2 1 1 a u a u a u r ' r r r r r r + + + = ' r r
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Bravais Space Lattices Space Lattices ¾ The most general (“lowest symmetry”) 2-D lattice is the “oblique lattice” in 2-D. ¾ a 1 and a 2 are called lattice translation vectors. Translation by integer multiple of a 1 and a 2 takes one from one lattice point to another ¾ There is an infinite number of lattices because there are no restrictions on the length or the angle ( α ) between the lattice translation vectors. ¾
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lecture_2_chex42 - Crystal Structure and Defects Crystal...

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