e4510lecture-5

e4510lecture-5 - J.W. Morris, Jr. University of California,...

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Unformatted text preview: J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Microstructure Microstructure : Type and location of all atoms in solid All atom positions known in only two ideal cases Perfect order ( crystals or quasi-crystals ) Perfect disorder ( amorphous solids or glasses ) Almost all solids prefer the crystalline state But perfect crystals are not possible in nature Describe by basic crystal structure + crystal defects 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, -ZnS ) Hcp-based ( -ZnS ) Bcc-based ( CsCl, Nb 3 Sn ) 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 ) 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 J.W. Morris, Jr.J....
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e4510lecture-5 - J.W. Morris, Jr. University of California,...

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