Melting of dense sodium

Area of Science:

• Materials Science
• Condensed Matter Physics
• High-Pressure Science

Background:

• Understanding the behavior of alkali metals under extreme conditions is crucial.
• Sodium's phase diagram at high pressures is not fully characterized.

Purpose of the Study:

• To investigate the melting curve and phase transitions of sodium (Na) at high pressures and temperatures.
• To extend the known melting curve of sodium to significantly higher pressures.

Main Methods:

• Utilized high-pressure, high-temperature synchrotron diffraction.
• Performed measurements up to 130 GPa and 1000 K.

Main Results:

• Observed a maximum on the melting curve of sodium in the body-centered cubic (bcc) phase at ~31 GPa and 1000 K.
• Identified a steep decrease in melting temperature for the face-centered cubic (fcc) phase.
• Discovered complex sodium phases forming above 103 GPa with unusually low melting temperatures (~300 K at 118 GPa).

Conclusions:

• The melting curve of sodium was extended to 130 GPa, revealing complex phase behavior.
• Unusually low melting temperatures were observed in high-pressure sodium phases.
• Further increases in pressure above 118 GPa led to increased melting temperatures.