Close Packing in Three Dimensions
All real structures are three dimensional structures that are obtained by stacking two dimensional layers one above the other in a square closepacked and hexagonal close-packed manner. It can be categorized into two types:
Three dimensional close packing from two dimensional square close-packed layers:
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The second layer is placed over the first layer in such a way that the spheres of the upper layer are exactly above those of the first layer.
In this arrangement of spheres, both the layers are perfectly aligned horizontally as well as vertically.
o Let the first row be‘ A’ type row, and the second row be‘ B’ type row. o Thus this lattice has AAA.... type pattern.
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The lattice therefore generated is the simple cubic lattice, and its unit cell is the primitive cubic unit cell.
Three dimensional close packing from two dimensional hexagonal close packed layers:
Three dimensional close packed structure can be generated by placing layers one over the other.
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Placing second layer over the first layer