Zinc has the hexagonal close–packed crystal structure. The lattice parameters for zinc are a = 0.26648 nm and c = 0.49470 nm, and the atomic radius is 0.1332 nm. Note that zinc does not have the ideal atomic packing factor.
(a) What is the number of atoms per unit cell in the hexagonal close–packed structure?
(b) Determine the atomic packing factor of the Zn unit cell.
(c) Is the c/a ratio for zinc greater than or less than the ideal HCP c/a ratio? Will slip be harder or easier in zinc compared to the ideal HCP structure? Explain your answer fully.