L11SimpCrStruc145s09

L11SimpCrStruc145s09 - Lecture 11: Basic Crystal Structures...

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Lecture 11, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Reading assignment : C&R §3.1-3.5; §3.9; §3.16; OGC §21.2 Learning objectives: Know characteristics of several simple crystal structures Body centered cubic Face-centered cubic (cubic close-packed) Hexagonal close-packed Diamond cubic Know how to compute atomic packing factor Lecture 11: Basic Crystal Structures
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Lecture 11, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Body-Centered Cubic (BCC) [OGC § 21.2] In BCC structure, all atoms are the same element (different colors are used here for visual clarity) Every atom has 8 nearest neighbors Coordinates occupied: Total of 2 atoms per unit cell: OGC Figure 21.12
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Lecture 11, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Body-Centered Cubic (BCC) [OGC § 21.2] Movie from “Visualizations in Materials Science,” Prof. John C. Russ, North Carolina State University
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Lecture 11, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Atomic packing factor Relationship between atomic radius r and lattice parameter a : Volume of atoms: Volume of cubic cell: Atomic packing factor: 4 3 r a = V atoms = 2 4πρ 3 3 = π3 8 α 3 V cell = α 3 APF = ς ατομσ χελλ = 8 = 0.68 Body-Centered Cubic (BCC) [C&R §3.4] C&R Figure 3.2
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Lecture 11, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Face-Centered Cubic (FCC) [OGC § 21.2] Coordinates occupied:
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L11SimpCrStruc145s09 - Lecture 11: Basic Crystal Structures...

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