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| Some Important Relations |
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 Relation between nearest
neighbor distance (d) and edge length (a) of a unit cell in a cubic crystal. |
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| 1. Simple cubic unit cell |
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| Distance between nearest neighbors |
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| (d) = AB = a for pure elements |
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| fig 2.1 |
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| 2. Face - centred cubic or ccp arrangement |
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| Distance between nearest neighbors |
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| fig 2.19 |
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| In the right angled triangle ABC, |
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| AC2 = AB2 + BC2 |
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| or = a2 + a2 = 2a2 |
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| \ From (i) and (ii) |
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| 3. Body - centre cube |
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| Distance between nearest neighbor |
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| fig 2.20 |
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| In the right angled triangle ABD |
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| Now in right angled triangle ACD, |
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