The recurrence of dense face-centered cubic cesium

Area of Science:

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

Background:

• Alkali metals like cesium (Cs) exhibit complex phase transitions under pressure.
• Cesium's known phases include body-centered cubic, face-centered cubic (fcc), oC84, tI4, oC16, and double hexagonal close-packed (dhcp).

Purpose of the Study:

• To investigate the high-pressure phase behavior of cesium beyond the dhcp phase.
• To predict and characterize novel high-pressure phases of Cs using computational methods.

Main Methods:

• First-principles structure searching prediction.
• Total-energy calculations.
• Transition state calculations.

Main Results:

• Cesium re-transforms to the fcc phase above 180 GPa, following the dhcp phase.
• This transition involves overcoming an energy barrier (144 meV/atom at 200 GPa) and a 0.3% volume collapse.
• The high-pressure fcc Cs phase shows distinct electronic properties, with d-electrons dominating the Fermi level and significant inner core electron overlap.

Conclusions:

• The fcc phase is a stable phase of cesium at extreme pressures.
• Similar phase transitions are predicted for potassium and rubidium at higher pressures.
• Understanding these transitions provides insight into the behavior of alkali metals under extreme conditions.