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Cubic closest packed (CCP) |
. |
Staggering the two triangulated layers so the spheres of one nestle in the
hollows |
of
the other forms the cubic closest packed (CCP) packing arrangement. It
is called |
. |
this because this is the densest way that spheres can be packed together to
fill 3D |
. |
space. When the sphere centers (nuclei) are connected together by
lines a lattice is |
. |
|
overhead view |
|
 |
 |
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Figure 37 - Cubic closest |
packing (CCP) of spheres |
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click image to enlarge |
. |
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|
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formed of tetrahedra and octahedra packed together in the space filling ratio
of 2:1 |
. |
respectively. |
. |
Things get a little more complicated when a third triangulated layer of
spheres |
. |
(atoms) is added to the previous two staggered CCP layers. Its spheres
can nestle |
in
the hollows of the second, topmost layer so that they are directly vertical
of (i.e. |
eclipse) the spheres of the first layer, or so that none of the spheres of
the three |
layers eclipse each other. |
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Hexagonal close packed (HCP) |
The eclipsed arrangement is called hexagonal closest packed (HCP). The
vertical |
. |
overhead view |
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 |
 |
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( 24 T, 12 pinges ) |
click
image to enlarge |
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Figure 38 - Hexagonal closest packed (HCP) sphere
packing |
. |
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arrangement of the spheres is ABA to indicate the eclipsing of the first
layer by the |
third. Note that the central sphere in this cluster is coordinated
with twelve other |
spheres - six spheres surrounding it in the same layer and three spheres in
both the |
lower and upper adjacent layers. This thirteen sphere cluster can be
modeled as |
a
"twist" cuboctahedron to emphasize the symmetry of the coordinated spheres. |
Back to
Knowhere |
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Page
27 - Structure matters - HCP packing |
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