Primitive Face Centered Cubic
In any lattice it is always possible to choose
a primitive (Z = 1) unit cell. In fact, there is an infinite number
of such choices, and it can be shown that all of the primitive unit cells
on a lattice have the same
volume. However, only one of these
primitive unit cells has the three shortest cell edges (a,b,c),
and this unit cell is called the standard reduced cell.
In a FCC lattice, the standard reduced
cell is a rhombohedron, with a = b = c = 2r. The three
interior angles formed between unit cell edges are called:
a (alpha,
between edges b & c)
b (beta,
between edges a & c)
g (gamma,
between edges a & b)
In the FCC rhombohedral standard reduced cell,
it can be shown that a
= b = g
= 60o. Note that
a cube is a just a special rhombohedron, with a
= b = g
= 90o.
(crossed stereo pair)
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