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# lecture10 - 13 Lecture 9 February 4 2008 See the powerpoint...

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13 Lecture 9, February 4, 2008 See the powerpoint presentation for this information.

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14 Lecture 10, February 6, 2008 4. Atomic positions in lattices must be shared, since the unit cells must directly touch each other to completely fill space. This means that only atoms that are completely contained within the boundaries of the unit cell can be counted as being completely part of that cell. For example, in any cubic unit cell the following positions are fractional: a. corner atoms: count 1/8 toward the cell b. edge atoms: count ¼ toward the cell c. face atoms: count ½ toward the cell D. Close-packing, holes 1. If the atoms are treated like hard spheres, then hexagonal layering will maximize the density within one two-dimensional layer. 2. However, the arrangements of one hexagonally arranged layer relative the next can differ. a. ABABA… "hexagonal close-packed" (hcp); hexagonal unit cell in three dimensions. b. ABCABC… "cubic close-packed" (ccp or fcc); face-centered cubic unit cell in three dimensions.
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lecture10 - 13 Lecture 9 February 4 2008 See the powerpoint...

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