Understanding the difference in fragility of the bcc phases of highly compressed P, As, and Sb through first-principles investigations

Among the pnictogens, the high-pressure phases of P show various structural transitions, while those of As and Sb do not. The body-centered-cubic (bcc) structure appears at 97 GPa in As and at 28.8 GPa in Sb. A transition from this strongly stable bcc structure to a new phase with further compression has not yet been reported in As or Sb in experimental or theoretical studies. The difference in the stability of the bcc structure between As (or Sb) and that of P is explained based on the investigations of the electronic structures using first-principles calculations. The occupied d orbitals of As and Sb play an important role in the stability of their respective bcc structures, while the absence of such in P causes an instability in the bcc structure making it comparatively fragile.