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Diamond
structure elements |
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C
(diamond), Si, Ge, a-Sn
(gray) |
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Crystal lattice |
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The diamond crystal lattice structure can be modeled as an expanded FCC
lattice |
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where one-half of the tetrahedral cluster of close packed atoms have another
equal |
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radius atom of the same species located in the center of the cluster.
But the volume |
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Figure 52 - Expanded FCC |
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diamond structure |
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of the central sphere is larger than the size of the interstitial void space
normally |
present in the center of a tetrahedral cluster of closest packed atoms.
This causes |
the atoms located at the corners of the cluster to expand apart to
accommodate the |
central atom so that they no longer touch each other, only the central atom.
Each |
atom of the diamond packing has a coordination number of four compared to
the |
twelve
coordinated atoms of a normal FCC packing. |
In the following model of the diamond lattice one-half of the tetrahedra are
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identified with an opaque color to indicate they contain a central atom
(unoccupied |
tetrahedral voids are blue). |
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click image to enlarge |
Figure 53 -
Diamond elements |
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lattice structure |
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Polyhedral framework |
The polyhedral framework of elements exhibiting the diamond structure can be |
modeled as a array of vertex linked tetrahedra with the understanding that
each |
tetrahedron contains a central equi-radius atom. |
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linking surfaces |
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Figure 54 - Polyhedral framework |
model of the diamond structure |
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4
vertices |
click image to enlarge |
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Back to
Knowhere |
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Page
36 - Structure matters - Diamond structure elements |
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