First principle study of intrinsic defects in hexagonal tungsten carbide

TL;DR

This study uses first-principles calculations to analyze intrinsic defects in hexagonal tungsten carbide, revealing defect stability, diffusion behaviors, and implications for material properties relevant to fusion reactor divertors.

Contribution

It provides new insights into defect formation energies, migration barriers, and defect behaviors in WC using first-principles methods, which were previously not well understood.

Findings

Carbon defects have lower formation energies than tungsten defects.

Carbon vacancies are stable over a wide temperature range due to high diffusion barriers.

Carbon interstitials migrate at lower temperatures due to lower activation energy.

Abstract

The characteristics of intrinsic defects are important for the understanding of self-diffusion processes, mechanical strength, brittleness, and plasticity of tungsten carbide, which present in the divertor of fusion reactors. Here, we use first-principles calculations to investigate the stability of point defects and their complexes in WC. Our calculation results confirm that the formation energies of carbon defects are much lower than that of tungsten defects. The outward relaxations around vacancy are found. Both interstitial carbon and interstitial tungsten atom prefer to occupy the carbon basal plane projection of octahedral interstitial site. The results of isolated carbon defect diffusion show that the carbon vacancy stay for a wide range of temperature because of extremely high diffusion barriers, while carbon interstitial migration is activated at lower temperatures for its considerable lower activation energy. These results provide evidence for the presumption that the 800K stage is attributed by the annealing out of carbon vacancies by long-range migration.