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| Diffusion | |||||||||||||||
| ·
For
an interstitial impurity in a bcc lattice
(such as carbon
in iron) two equivalent interstitial
sites exist as shown in the diagram. It is necessary to compute the number
of such sites on a given {100} plane.
* Number of Type 1 sites = 4 x ½ = 2 * Number of Type 2 sites = 4 x ¼ = 1 * Total number of sites per unit cell = 3 * Only interstitials on Type 1 sites can jump to the next cell, therefore, the Jumping Fraction = (2/3) |
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| ·
Only
one jump path couples each site to the next cell. Number of Paths = 1
· Combining the jumping fraction and the number of paths gives: α = (2/3) · For this case: D0 = (2/3)να2 |
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