| Abstract Scope |
Zirconium carbide (ZrC) is a promising ultra-high-temperature ceramic for extreme environments, but its performance is controlled by defect formation, migration, and carbon transport. In this presentation, we combine density functional theory (DFT) and machine learning interatomic-potential molecular dynamics (MLIP-MD) to examine how defects, charge carriers, temperature, and pressure govern carbon mobility in ZrC. DFT calculations show that isolated carbon vacancies have the lowest formation energy, followed by Frenkel pairs, whereas divacancies and Schottky pairs are less favorable. Charge doping modifies migration barriers in a defect-specific manner by altering local Zr–C bonding. MLIP-MD simulations from 2000 to 3500 K and pressures up to 2 GPa further reveal distinct diffusion mechanisms in stoichiometric ZrC and carbon-deficient ZrC0.9. In ZrC0.9, carbon vacancies promote local hopping at lower temperatures but trap thermally generated interstitials at higher temperatures, suppressing long range diffusion and causing a diffusion crossover near 2600–2700 K. |