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| Efficiency of packing in hcp and ccp structures |
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| We have discussed earlier that in both type of close packing (hcp and ccp) approximately amount of the available volume is occupied by spheres (atoms). |
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| 1. Let us calculate the efficiency of packing in ccp structure |
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| (FCC arrangement) |
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| We have found that for a ccp arrangement |
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| We also know that, per unit cell in ccp arrangement has effectively 4 spheres. |
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| Therefore, |
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| Percentage efficiency |
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| 2. Efficiency of body centered cubic structures |
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| We know, for a bcc structure |
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| In bcc structure, the total number of atoms per unit cell is 2. |
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| Volume of the cube = a3 |
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| Therefore, |
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| Percentage efficiency |
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| = 68% |
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| Therefore, |
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 Relation between atomic radius r (which is d/2 for pure elements) and a the edge unit cell of a cubic crystal. |
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