Structural Systematics of the High-Pressure Phases of Phosphorus, Arsenic, Antimony and Bismuth

New structural systematics of the high-pressure phases of the title elements are given on the basis of the results obtained in our diffraction studies and the results from the literature. Although the structural transition sequence with increasing pressure appears to be different for the four elements, reinterpretation of the structure data has shown that it is expressed in a systematic way as follows P A 17– A 7–PSC As A 7–PSC–dist. BCC–BCC Sb A 7–dist. BCC–BCC Bi A 7–dist. PSC–dist. BCC–BCC. Notations used are A 17 (orthorhombic layered structure), A 7 (rhombohedral layered structure), PSC (primitive simple cubic structure), dist. PSC (monoclinic structure which is regarded as a distorted PSC), BCC (body-centered cubic structure) and dist. BCC (tetragonal structure which is regarded as a distorted BCC). Phosphorus lacks the post-PSC phases, but it is likely that the same transition sequence as that of arsenic is seen under extremely high pressure. Discussion is made on how the network of the densest atomic plane changes through the structural transition sequence.