LECTURE 16 Crystalline sites

LECTURE 16 Crystalline sites - SUMMARY FROM LAST CLASS...

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Dr. P. Lucas U of A MSE 110 Crystalline solids For all types of solids, every atomic bonds have maximum energy at a specific distance r o , hence ordered crystalline arrangements are energetically favored. When atoms or spherical molecule do not favor any particular bonding directions, they behave as hard sphere and the bonding is maximized by adopting high packing density. These close packed structures are formed by stacking dense atomic layers. Faced Center Cubic : (FCC) ABCABC. .. sequence. 4 atoms per cubic cell. Hexagonal Close Packed :(HCP) ABAB… sequence. 6 atoms per hexagonal cell. a/c=1.633 Body Centered Cubic : (BCC) 2 atoms per cubic cell. SUMMARY FROM LAST CLASS 2 2 R a = R a 3 4 =
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Dr. P. Lucas U of A MSE 110 Packing density: The packing density can be calculated for each structure by taking the ratio of the volume of the spheres included in the cell versus the cell volume itself. CRYSTALLINE STRUCTURE FCC has the same packing density as HCP and is the densest of all structures. % 74 ) 2 2 ( 4 3 3 3 4 4 = × = R R cell of Volume atom of Volume π % 68 ) ( 2 3 3 4 3 3 4 2 = × = R R cell of Volume atom of Volume % 52 ) 2 ( 3 3 3 4 1 = = R R cell of Volume atom of Volume SIMPLE CUBIC: 1 atom per cell Packing density= BODY CENTERED CUBIC: 2 atoms per cell Packing density= FACE CENTERED CUBIC: 4 atoms per cell Packig density=
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Dr. P. Lucas U of A
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This note was uploaded on 10/06/2009 for the course MSE 110 taught by Professor Lucas during the Spring '08 term at University of Arizona- Tucson.

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LECTURE 16 Crystalline sites - SUMMARY FROM LAST CLASS...

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