Density functional study of PuC and PuC_0.75O_0.25.

Area of Science:

• Materials Science
• Computational Physics
• Plutonium Chemistry

Background:

• Plutonium carbide (PuC) is a key material in nuclear applications.
• Understanding its structural, magnetic, and thermodynamic properties is crucial for safety and performance.
• The influence of oxygen substitution on PuC properties requires detailed investigation.

Purpose of the Study:

• To comprehensively study the structural, magnetic, electronic, thermodynamic, and elastic properties of PuC and PuC0.75O0.25.
• To elucidate the impact of carbon-oxygen substitution on PuC's material characteristics.
• To determine the driving force behind the oxidation and aging of PuC.

Main Methods:

• Utilized density-functional theory (DFT) and DFT + U calculations.
• Investigated nonmagnetic (NM), ferromagnetic (FM), and antiferromagnetic (AFM) configurations.
• Calculated total energies, electronic density of states, thermodynamic parameters, elastic constants, and defect formation energies.

Main Results:

• PuC0.75O0.25 exhibits an antiferromagnetic ground state, consistent with PuC.
• Oxygen substitution introduces a new peak in the density of states and enhances thermodynamic properties (enthalpy, entropy, heat capacity).
• PuC0.75O0.25 is predicted to be harder due to stronger Pu-O bonds, and the oxygen-substitution defect formation energy is highly spontaneous (-5.11 eV).

Conclusions:

• The spontaneous formation energy of oxygen defects confirms a fundamental driving force for PuC oxidation and chemical aging.
• PuC0.75O0.25 demonstrates distinct thermodynamic and elastic properties compared to PuC.
• These findings provide essential data for future theoretical and experimental studies on PuC and its oxygenated forms.