Measurement of Body-Centered Cubic Gold and Melting under Shock Compression

Area of Science:

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

Background:

• Gold (Au) is a critical calibration standard in high-pressure experiments, known for its stable face-centered cubic (fcc) structure.
• Theoretical models predict complex fcc-like structures in gold at intermediate high pressures, contrasting experimental observations.

Purpose of the Study:

• To investigate the crystallographic state of gold (Au) under shock compression conditions.
• To experimentally determine the high-pressure phases of gold and compare them with theoretical predictions.

Main Methods:

• Utilized laser shock compression to achieve high pressures and temperatures in gold samples.
• Employed in situ X-ray diffraction to probe the crystal structure of gold during shock compression.

Main Results:

• Observed the face-centered cubic (fcc) phase of gold at 169 GPa.
• Provided the first experimental evidence of body-centered cubic (bcc) gold at 223 GPa.
• Detected coexistence of the bcc phase and liquid scattering near the melting curve before 322 GPa.

Conclusions:

• The experimental results challenge existing theoretical models of gold's high-pressure behavior.
• Suggest the existence of a triple point in the gold phase diagram near 220 GPa, close to the principal shock Hugoniot.