Real crystal structures: Consider the hep lattice shown in Figure 2.14. The Bravais lattice underlying the hcp structure is given by two vectors of length a in one plane, with an angle of 60° between them and a third vector of length c perpendicular to that plane. There are two atoms per unit cell. (a) Show that for the ideal packing of spheres, the ratio c/a= (8/3)'2. (b) (*) Construct the reciprocal lattice. Does the fact that there are two atoms per unit cell in the hcp crystal has any relevance?

Real crystal structures: Consider the hep lattice shown in Figure 2.14. The Bravais lattice underlying the hcp structure is given by two vectors of length a in one plane, with an angle of 60° between them and a third vector of length c perpendicular to that plane. There are two atoms per unit cell. (a) Show that for the ideal packing of spheres, the ratio c/a= (8/3)'2. (b) (*) Construct the reciprocal lattice. Does the fact that there are two atoms per unit cell in the hcp crystal has any relevance?