Ba-IV-Type Incommensurate Crystal Structure in Group-V Metals

The long-unknown crystal structure of Bi-III has been solved. It comprises a body-centered-tetragonal (bct) “host” and a bct “guest” component made up of chains that lie in channels in the host; the guest is incommensurate with the host along the tetragonal $c$ axis. Diffraction data for Sb-II reveal that it too can be fitted with the same composite structure. The structures of these two high-pressure phases of Bi and Sb are similar to those reported recently in the alkaline-earth metals Ba and Sr.