The unit cell A can be translated in directions a 2 and b 2 , the unit cell B can
be translated in directions a 3 and b 3 , and the entire two-dimensional lattice can be
constructed by the translations of either of these unit cells. The unit cells C and D
in Figure 1.3 can also be used to construct the entire lattice by using the appropriate
translations. This discussion of two-dimensional unit cells can easily be extended to
three dimensions to describe a real single-crystal material.