A transition path for the pressure-induced wurtzite- to NaCl-type transformation described in Pna2₁

Quite recently, two further mechanisms for the pressure-induced transition from the wurtzite to the NaCl type were proposed [Shimojo et al. (2004). Phys. Rev. B, 70, 184111-1-6] but no symmetry information was given. It will be shown that a slight modification of one of the assumed transition pathways allows a crystallographic description on the basis of a deformation of a heterogeneous 4-connected sphere packing in Pna2₁. All investigations were done with the help of the corresponding homogeneous packing in Pnma where the transition may be described as a deformation of a lonsdaleite configuration into a cubic primitive lattice cP. During the transformation, all sphere contacts are maintained. The new transition model is compared with the well known Cmc2₁ mechanism. Further related mechanisms can also be derived.