Solving a problem with a single parameter: a smooth bcc to fcc phase transition for metallic lithium

Area of Science:

• Solid-state physics
• Materials science
• Computational chemistry

Background:

• Metallic lithium exhibits complex phase behavior.
• The relative stability of body-centered cubic (bcc) and face-centered cubic (fcc) phases in lithium has been a subject of debate.
• Understanding phase transitions is crucial for materials applications.

Purpose of the Study:

• To computationally investigate the phase transformation pathway between the bcc and fcc phases of metallic lithium.
• To resolve the long-standing controversy regarding the dominant phase of lithium under varying conditions.
• To elucidate the energetic landscape governing the bcc-fcc transition.

Main Methods:

• Density functional theory (DFT) calculations were employed.
• A cuboidal transformation path between bcc and fcc structures was defined.
• Thermodynamic principles, including Landau theory, were applied to interpret results.

Main Results:

• The bcc and fcc phases of metallic lithium are found to be quasi-degenerate.
• A very small activation barrier (0.1 kJ/mol) exists for the bcc-to-fcc transformation.
• The bcc phase becomes dominant at higher temperatures, consistent with Landau theory predictions.

Conclusions:

• The study provides a theoretical resolution to the phase stability controversy in metallic lithium.
• The calculated low activation barrier explains the facile interconversion between bcc and fcc phases.
• Temperature-dependent phase dominance is explained by thermodynamic principles.