Engineering Physics

2.13 Stacking sequence in metallic crystals

To minimize the potential energy of a metallic crystal, the atoms in it are very closely packed. A close packing is a way of arranging equidimensional objects in space so that the available space is filled very effectively. In metallic crystals, the atoms are assumed to be hard, incompressible spheres. If we have equal-sized spheres, then a closest packing of like spheres is that the arrangement in which each sphere to form an intimate contact with a large number of its neighbours, occupying the available space most efficiently.

A closest packed layer of equal-sized atoms is shown in Fig. 2.19(a), the sites of atoms are represented as ‘A’, each sphere has six nearest neighbours in a closest packed layer ...