Ba-IV-type incommensurate crystal structure in group-V metals

Area of Science:

• Solid-state chemistry
• Crystallography
• Materials science

Background:

• The high-pressure phases of bismuth (Bi) and antimony (Sb) have complex crystal structures that remain poorly understood.
• Previous studies have indicated unique structural transitions in these elements under extreme conditions.

Purpose of the Study:

• To determine the long-unknown crystal structure of bismuth-III (Bi-III).
• To investigate the structural characteristics of antimony-II (Sb-II) under high pressure.
• To compare the observed structures with those of other elements under similar conditions.

Main Methods:

• Analysis of diffraction data to solve crystal structures.
• Utilizing a composite structure model involving body-centered-tetragonal (bct) host and guest components.
• High-pressure experimentation and structural characterization.

Main Results:

• The crystal structure of Bi-III was solved, revealing a composite structure consisting of a body-centered-tetragonal (bct) host and a bct guest component.
• The guest component, composed of chains within the host's channels, is incommensurate with the host along the c-axis.
• Diffraction data for antimony-II (Sb-II) confirmed it shares the same composite structure as Bi-III.
• The determined structures bear resemblance to recently reported high-pressure phases in alkaline-earth metals like barium (Ba) and strontium (Sr).

Conclusions:

• The crystal structure of Bi-III is a composite type, featuring incommensurate host and guest components.
• Antimony-II (Sb-II) exhibits a similar composite crystal structure under high pressure.
• These findings highlight a shared structural motif in high-pressure phases of diverse elements, including post-transition metals and alkaline-earth metals.