Chain disorder induced by the bonding polarity in the incommensurate structure of antimony

The chain disordering transition, often observed in incommensurate host-guest (HG) systems, has never been observed in antimony, and the underlying mechanism remains poorly understood. Here, the x-ray diffraction results show that, upon decompression from 12 GPa to ambient pressure at 90 K, the incommensurate HG structure of Sb-II transforms into a new incommensurate structure with chain disorder, while the host framework maintains its tetrahedral structure. This is distinct from the structural evolution observed at room temperature. The density functional theory calculation reveals the structural modulation of the guest chains evolving from the uniform distribution with metallic bonds at high pressure (>15 GPa) to the atomic pairing with enhanced host-guest bonding polarity at ambient pressure. The atomic pairing and bonding polarized behaviors at low pressure are likely the driving force for the chain disordering during decompression. Moreover, the phonon calculation shows that there are two low-frequency quasiacoustic modes associated with pressure-induced chain disordering and intraphase transitions. This study advances the understanding of the HG structural evolution through host-guest interactions, offering insights into pressure modulation in the incommensurate phases.