lectures8_9

# lectures8_9 - A A A A A A A B B B B B B B A A A A A A A B B...

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p4mm Valid unit cells Invalid unit cells Examples of unit cells on a square lattice

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Valid unit cells Invalid unit cells Examples of unit cells on a non-square lattice
Comparison of trigonal and hexagonal symmetries 3-fold rotation 6-fold rotation 3-fold rotation

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p4gm p4 p4mm Mirror planes in related lattices (no mirrors)
Where is the unit cell in this pattern? a b dot = “two-fold rotation”

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Examples of unit cells in 3D
Comparison of related 3D lattices Face-centered cubic (fcc) Primitive cubic (pc)

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Not close-packed Close-packed Close-packing in a 2D layer

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Unformatted text preview: A A A A A A A B B B B B B B A A A A A A A B B B B B B B A A A A A A A A A A A A A A B B B B B B B C C C C C C C Generation of hcp and fcc polytypes A A A A A A A A B A A B C • hexagonal close-packed , hcp • hexagonal unit cell • # of nearest neighbors … … = 12 coordination number =12 • cubic close-packed , ccp • also, face-centered cubic , fcc • cubic unit cell • coordination number … … = 12 packing efficiency (amount of space occupied within each unit cell) = 74%...
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## This note was uploaded on 04/18/2008 for the course CHEM 131 taught by Professor Landry during the Spring '08 term at Vermont.

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lectures8_9 - A A A A A A A B B B B B B B A A A A A A A B B...

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