e4510lecture-6

e4510lecture-6 - Crystal Structures of Interest Elemental...

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J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Crystal Structures of Interest Elemental solids: – Face-centered cubic ( fcc ) – Hexagonal close-packed ( hcp ) – Body-centered cubic ( bcc ) – Diamond cubic ( dc ) Binary compounds – Fcc-based ( Cu 3 Au,NaCl, ß-ZnS ) – Hcp-based ( α -ZnS ) – Bcc-based ( CsCl, Nb 3 Sn )
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J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 The Common Crystal Structures: Body-Centered Cubic (BCC) Atoms at the corners of a cube plus one atom in the center Is a Bravais lattice, but drawn with 2 atoms/cell to show symmetry Bcc is not ideally close-packed Closest-packed direction: <111> Closest-packed plane: {110} Common in Alkali metals ( K, Na, Cs ) Transition metals ( Fe, Cr, V, Mo, Nb, Ta )
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J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 The Face-Centered Cubic (fcc) and Hexagonal Close-Packed (hcp) Structures Fcc: atoms at the corners of the cube and in the center of each face Is a Bravais lattice , but drawn with 4 atoms/cell to show symmetry Found in natural and noble metals: Al, Cu, Ag, Au, Pt, Pb Transition metals: Ni, Co, Pd, Ir Hcp: close-packed hexagonal planes stacked to fit one another Does not have a primitive cell (two atoms in primitive lattice of hexagon) Divalent solids: Be, Mg, Zn, Cd Transition metals and rare earths: Ti, Zr, Co, Gd, Hf, Rh, Os
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J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Hexagonal Close-Packed HCP does not have a primitive cell 2 atoms in primitive cell of hexagonal lattice 6 atoms in cell drawn to show hexagonal symmetry Common in Divalent elements : Be, Mg, Zn, Cd Transition metals and rare earths : Ti, Zr, Co, Gd, Hf, Rh, Os Anisotropy limits engineering use of these elements
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J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Face-Centered Cubic Structure FCC is cubic stacking of close-packed planes ( {111} ) 1 atom in primitive cell; 4 in cell with cubic symmetry <110> is close-packed direction
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e4510lecture-6 - Crystal Structures of Interest Elemental...

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