Diverse carbon units in high-pressure C-K system predicted from first-principles and machine-learning methods

Area of Science:

• Materials Science
• Solid State Chemistry
• Computational Materials Science

Background:

• Metal-carbon compounds offer diverse carbon structures with unique electronic properties.
• Understanding phase diagrams is crucial for discovering novel materials.
• Previous research has explored various carbon allotropes and their applications.

Purpose of the Study:

• To construct a detailed phase diagram for the carbon-potassium (C-K) system.
• To identify and characterize novel carbon structures and their properties.
• To explore the potential applications of newly discovered carbon materials.

Main Methods:

• Crystal structure prediction using the MAGUS method.
• Machine-learning potentials fitted from first-principles calculations.
• Boltzmann transport calculations for electrical conductivity.
• Adsorption energy calculations for gas interactions.

Main Results:

• A comprehensive C-K phase diagram was generated, revealing diverse carbon units.
• The Pnma C12K16 phase was identified to contain insulating allylenide ions.
• A stable Cmcm C12K4 phase features "σ-graphene" with unique 5-6-7 carbon rings.
• Pristine σ-graphene exhibits high electrical conductivity (∼5.5 × 10^7 S/m), comparable to silver and copper.
• σ-graphene shows excellent adsorption for O2 and NO2, indicating potential in catalysis and environmental monitoring.

Conclusions:

• The C-K system is a versatile platform for novel carbon material synthesis.
• σ-graphene is a promising material for electrical transport applications due to its high conductivity.
• The unique properties of σ-graphene suggest potential uses in catalysis and environmental sensing.