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-centend-tetragonal (bct) "host" and a bet "guest" component made up of chains that lie in channels in the host; the guest is incommensurate wit h the host along the tetragonal c axis. Diffraction data for Sb-II reveal t hat 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 reporte d recently in the alkaline-earth metals Ba and Sr.