Multimegabar stability of bcc antimony and high-pressure systematics of neighboring group-15 elements

We extend the equation of state and phase stability of body-centered cubic (bcc) antimony (Sb) into the multimegabar regime using both first-principles calculations up to 436 GPa and experimental synchrotron x-ray diffraction in the diamond-anvil cell up to 258(6) GPa using Ne as a soft pressure-transmitting medium. We observe the complete sequence of pressure-induced phase transitions from Sb's A7 rhombohedral phase through the intermediate pressure incommensurate structures, including evidence for Sb-IV, and identify the onset of the bcc phase between 28.9(5) and 30.3(6) GPa. The high-pressure volumetric response of the bcc phase was fit to a third-order Vinet equation of state with parameters of ${V}_{0}=26.28(32)\phantom{\rule{0.28em}{0ex}}{\AA{}}^{3}/\mathrm{atom}, {K}_{0}=66.50(47)\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$, and ${K}^{\ensuremath{'}}=4.97(2)$. Density-functional theory confirms the stability and characterizes the elastic properties of bcc Sb up to 436 GPa. A Comparison with bcc As and Bi highlights the systematic trends in compressibility and electronic structure across these group-15 elements.