Lecture 3 - 8th Ed. Ch. 3

Lecture 3 - 8th Ed. Ch. 3 - Chapter 3 The Structure of...

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1 Chapter 3 The Structure of Crystalline Solids
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2 ISSUES TO ADDRESS. .. How do atoms assemble into solid structures? (for now, focus on metals) How does the density of a material depend on its structure? When do material properties vary with the orientation in a crystal? (Isotropic vs. anisotropic)? The Structure of Crystalline Solids
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3 Non dense, random packing Dense, ordered packing Dense, ordered packed structures tend to have lower energies, i.e. thermodynamically more stable Energy and Packing Energy r typical neighbor bond length typical neighbor bond energy Energy r typical neighbor bond length typical neighbor bond energy
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4 atoms pack in periodic, 3D arrays Crystalline materials. .. -metals -many ceramics -some polymers atoms have no periodic packing Noncrystalline materials. .. -complex structures -rapid cooling crystalline SiO 2 noncrystalline SiO 2 " Amorphous " = Noncrystalline Materials and Packing Si Oxygen typical of: occurs for:
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5 Metallic Crystal Structures How can we stack metal atoms to minimize empty space? 2-dimensions vs. Now stack these 2-D layers to make 3-D structures
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6 Crystal Systems 7 crystal systems 14 crystal lattices (Bravais lattices) Unit cell: smallest repetitive volume which contains the complete lattice pattern of a crystal. a, b, and c are the lattice constants
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7 The 14 Bravais Lattices Courtesy of P. Davies (UPenn)
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8 Crystal Class Axes Designation Cubic a=a 1 =a 2 =a 3 α= = =90 o Tetragonal a=a 1 =a 2 ; c=a 3 ; a c α= = =90 o Orthorhombic a=a 1 b= a 2 c=a 3 α= = =90 o Hexagonal a=a 1 =a 2 c=a 3 α= =90 o ; =120 o Rhombohedral a=a 1 =a 2 =a 3 α 90 o ; = =90 o Monoclinic a=a 1 b= a 2 c=a 3 α 90 o ; = =90 o Triclinic a=a 1 b= a 2 c=a 3 α 90 o ;  90 o ;  90 o α   90 o Symmetry The 14 Bravais Lattices
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CsCl NaCl Courtesy of Encyclopedia Britannica CsCl & NaCl Structures
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YBCO Superconductor Structure Orthorhombic unit cell!
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Diamond ZnS Diamond and ZnS Structures
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ZrO 2 (Fluorite) Lattice
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13 Tend to be densely packed. Reasons for dense packing: - Typically, only one element is present, so all atomic radii are the same. - Metallic bonding is not directional. - Nearest neighbor distances tend to be small in order to lower bond energy. - Electron cloud shields cores from each other Have the simplest crystal structures. We will examine three such structures. .. Metallic Crystal Structures
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14 Rare due to low packing denisty (only Po has this structure) Close-packed directions are cube edges. Coordination # = 6 (# nearest neighbors) (Courtesy P.M. Anderson) Simple Cubic Structure (SC)
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15 Coordination # = 8 Adapted from Fig. 3.2, Callister 7e. (Courtesy P.M. Anderson) Atoms touch each other along cube diagonals.
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This note was uploaded on 02/20/2012 for the course MSE 14:635:407 taught by Professor Dr.e.korayakdoğan during the Spring '12 term at Rutgers.

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Lecture 3 - 8th Ed. Ch. 3 - Chapter 3 The Structure of...

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