Pressure-induced structural transformation of CaC2

Area of Science:

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

Background:

• Calcium carbide (CaC2) exhibits complex structural behavior under varying conditions.
• Understanding its phase transitions is crucial for materials science applications.

Purpose of the Study:

• To investigate the high-pressure structural transformations of calcium carbide (CaC2).
• To characterize the phase transitions using advanced spectroscopic and diffraction techniques.

Main Methods:

• Raman spectroscopy and synchrotron X-ray diffraction (XRD) were employed.
• Experiments were conducted using a diamond anvil cell at room temperature.
• Pressure-induced structural changes were monitored.

Main Results:

• A phase transition from monoclinic CaC2-ii to CaC2-i occurred above 4.9 GPa.
• CaC2-i transformed into a metallic Cmcm structure with polymerized carbon chains at approximately 7.0 GPa, causing a 22.4% volume collapse.
• Irreversible amorphization was observed above 30.0 GPa.

Conclusions:

• High pressure induces significant structural changes in calcium carbide, including polymerization and amorphization.
• The metallic Cmcm phase represents a novel high-pressure state of CaC2.
• The observed irreversible amorphization suggests potential limitations for CaC2 under extreme pressures.