On the transition from the wurtzite to the NaCl type.

A crystallographic interpretation of a possible transition mechanism from the wurtzite to the NaCl type is given. For this purpose, different atoms in the structures of both types are replaced by like ones, resulting in lonsdaleite-type configurations and in cubic primitive lattices, respectively. The atomic arrangements of both types correspond to homogeneous sphere packings. It is shown that a lonsdaleite configuration may be deformed into a cubic primitive lattice within the Wyckoff position Cmcm 8(f) m. 0,y,z. Such a transition is displacive since no bonds have to be broken. The corresponding phase transformation from the wurtzite to the NaCl type can be described as a deformation of a heterogeneous sphere packing. The intermediate structure would have the symmetry Cmc2(1).