Local structure of solid Rb at megabar pressures

Area of Science:

• Condensed matter physics
• Materials science
• High-pressure physics

Background:

• Solid rubidium (Rb) exhibits complex phase transitions under extreme pressure.
• Understanding its structural and electronic properties is crucial for materials science.

Purpose of the Study:

• To investigate the local and electronic structure of solid rubidium up to 101.0 GPa.
• To confirm the predicted stability of phase VI of solid Rb.
• To analyze the pressure dependence of structural parameters and mean-square relative displacement.

Main Methods:

• X-ray absorption spectroscopy (XAS) was employed up to 101.0 GPa.
• Nanocrystalline diamond anvils were used to avoid signal-spoiling Bragg peaks.
• A high-performance X-ray focusing device provided a stable micro-beam spot size.
• Advanced data analysis extracted pressure-dependent structural parameters.

Main Results:

• The stability of phase VI of solid rubidium was confirmed at high pressures.
• Nearest neighbor distances in phase VI Rb continuously reduced by approximately 6% over the pressure range.
• The Grüneisen parameter for high-pressure Rb phase VI was estimated to be between 1.3 and 1.5.

Conclusions:

• The study successfully extended the experimental pressure range for solid rubidium investigations.
• Nanocrystalline diamond anvils and advanced XAS techniques enable precise high-pressure studies.
• The findings provide valuable insights into the behavior of alkali metals under extreme compression.