Crystal-liquid phase relations in silicon at negative pressure

Area of Science:

• Materials Science
• Computational Physics
• Chemistry

Background:

• Silicon's diverse crystal structures are crucial for technological applications.
• Understanding silicon's behavior under extreme pressure is essential for materials design.
• Previous studies have primarily focused on positive pressures, limiting insights into negative pressure regimes.

Purpose of the Study:

• To investigate the melting behavior of silicon in diamond and clathrate-II structures under both positive and negative pressures.
• To determine the thermodynamic stability of different silicon phases at negative pressures.
• To explore the mechanical instabilities and phase transitions of silicon under tension.

Main Methods:

• Molecular dynamics computer simulations were employed to calculate melting relations.
• Simulations covered a range of positive and negative pressures, including cavitation thresholds.
• Thermodynamic stability was assessed by comparing free energies of different phases.

Main Results:

• Cavitation in simulated liquid and crystalline clathrates was observed at approximately -3 and -12 GPa.
• A stretched silicon crystal can transform directly to gas due to mechanical instability.
• The clathrate-II crystal structure becomes thermodynamically stable over the diamond structure below -1 GPa at the melting point.

Conclusions:

• Silicon clathrate-II is a stable phase at negative pressures, offering potential for new material properties.
• The findings challenge conventional understanding of silicon's phase diagram under tension.
• This research provides critical data for designing silicon-based materials for extreme environments.