ch3 - Chapter III Chapter Structure of Crystalline Solids...

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Chapter III Chapter III Structure of Crystalline Solids Structure of Crystalline Solids
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Atomic packing in solids Atomic packing in solids Short Short - - range order vs. range order vs. Long Long - - range range order order
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Crystalline versus Non-crystalline Materials • atoms pack in periodic, 3D arrays • typical of: Crystalline materials. .. -metals -many ceramics -some polymers • atoms have no periodic packing • occurs for: Noncrystalline materials. .. -complex structures -rapid cooling crystalline SiO 2 noncrystalline SiO 2 " Amorphous " = Noncrystalline Adapted from Fig. 3.18(b), Callister 6e. Adapted from Fig. 3.18(a),
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Fundamental Concepts of crystal ± Lattice A three dimensional array of points. --useful for revealing the geometrical relations between atoms. ± Unit Cell a basic crystal unit and represent the symmetry of crystal structure Lattice of unit cell Unit Cell
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Lattice parameters A crystal structure is determined by axial lengths (a, b, c) and inter-axial angles.
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The Seven Crystal Systems Cubic Tetragonal Orthorhombic
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The Seven Crystal Systems Rhombohedral Hexagonal Monoclinic Triclinic
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Coordination Number
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Atomic Packing Factor (APF ) 6 APF = Volume of atoms in unit cell* Volume of unit cell *assume hard spheres APF for a simple cubic structure = 0.52 APF = a 3 4 3 π (0.5a) 3 1 atoms unit cell atom volume unit cell volume close-packed directions a R=0.5a contains 8 x 1/8 = 1 atom/unit cell
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Three Primary Structures of Metals Hexagonal Close-packed (HCP) Body-centered cubic (BCC) Face-centered cubic (FCC)
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The Crystal Systems in Metals Face-centered cubic (FCC) Crystal Structure APF: 0.74 Coordination No.: 12 (4 atoms/cell)( 4 / 3 π r 3 ) a o 3 Packing factor = For example: Al, Cu, Ni, Au, Ag, Fe( γ )
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ch3 - Chapter III Chapter Structure of Crystalline Solids...

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