Structure of polymeric carbon dioxide CO2-V

Area of Science:

• Materials Science
• High-Pressure Physics
• Solid-State Chemistry

Background:

• Polymeric carbon dioxide (CO2-V) is a high-pressure phase of CO2.
• Understanding its structure and properties is crucial for materials science and geochemistry.
• Previous studies have yielded limited structural and compressibility data.

Purpose of the Study:

• To determine the precise crystal structure of polymeric carbon dioxide.
• To investigate the compressibility of CO2-V under hydrostatic conditions.
• To compare experimental findings with theoretical predictions.

Main Methods:

• Synchrotron X-ray powder diffraction was employed to analyze CO2-V samples.
• Experiments were conducted across a pressure range of 8 to 65 GPa.
• A CO2/He mixture was used to achieve hydrostatic conditions and obtain pure CO2-V.

Main Results:

• The crystal structure of CO2-V was solved and found to be isomorphic to beta-cristobalite (SiO2), space group I42d.
• CO2-V features CO4 tetrahedral units linked by oxygen atoms.
• The bulk modulus (B0) was determined to be 136(10) GPa under hydrostatic conditions, which is lower than prior estimates.
• Density functional theory calculations accurately predicted the structure and properties of CO2-V.

Conclusions:

• The definitive structure of polymeric carbon dioxide has been elucidated.
• The determined bulk modulus provides a more accurate understanding of CO2-V compressibility.
• Density functional theory is a reliable tool for modeling polymeric carbon dioxide.