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THE HEXAGONAL CLOSE-PACKED STRUCTURE |
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The hexagonal -close packed structure arises when close-packed layers are stacked in an AB fashion so that the third layer lies over the first, the fourth layers lies over the second, and so forth. The hexagonal close-packed structure is adopted by many different metals, including Be, Mg, Sc, Ti, Co, and Zn. In addition, there are several ionic structures in which one set of ions forms a hexagonal close-packed structure and the other set of ions fits into the octahedral or tetrahedral holes. |
| This picture shows a top view of the previous model. Note that one one red layer is shown since one lies immediately on top of the other. The same applies to the blue layers. The holess in the center structure are octahedral holes, formed by three atoms within a single layer and three atoms in the layer above or below. These holes exist in the ABC-stacked structure as well. However, in the case of the AB-stacked layers the holes are distributed through the structure in such a way as it is possible to see all the way through the structure. |  |
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OCTAHEDRAL HOLES
This model shows the location of all the tetrahedral and octahedral holes within a series of ABAB hexagonal layers. The yellow spheres represent the tetrahedral holes; the green spheres represent the octahedral holes. |
| This picture shows the octahedral holes in AB-stacked hexagonal layers as seen from the top. Compare this to the top view show above. Can you find the location of the tetrahedral holes? |  |
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TETRAHEDRAL HOLES
This illsutration shows the location of the tetrahedral holes within a a series of AB-stacked hexagonal layers. The actual locations of the tetrahedral holes are much clearer seen from the top. |
| This image the tetrahedral holes within a series of AB-stacked hexagoal layers. This an isometric view and therefore lacks depth perspective, but the location of the octahedral and tetrahedral holes can clearly be seen. The three larger holes though the center of the structure are the octahedral holes. |  |
Additional Links
Crystal Structure Home Page
Introduction to Close-Packed Structures
The Hexagonal Close-Packed Structure
The Face-Centered Cubic Lattice
The Halite Structure
The Fluorite Structure
The Zinc Blende Structure
The Diamond Structure