The Cu–Zn system is characterised by structural changes. Copper
and a-brass have the fcc-structure, whereas zinc crystallises
in the hcp-lattice. The primitive cell of the fcc-structure contains
only one atom having 3 acoustic vibrational modes. On the other
hand, the primitive cell of the hcp-structure contains two crystallographic
different sites, resulting in 3 acoustic and 3 optical