First principle study of hydrogen behavior in hexagonal tungsten carbide

TL;DR

This study uses first-principles calculations to analyze hydrogen behavior in hexagonal tungsten carbide, revealing stable sites, interactions with vacancies, and diffusion pathways relevant for fusion reactor materials.

Contribution

It provides detailed atomic-level insights into hydrogen trapping, migration, and interactions in WC, advancing understanding for fusion reactor applications.

Findings

Hydrogen prefers specific interstitial sites in WC.

Hydrogen is trapped by vacancies but does not form H2 molecules.

Hydrogen diffuses mainly along the c axis.

Abstract

Understanding the behavior of hydrogen in hexagonal tungsten carbide (WC) is of particular interest for fusion reactor design due to the presence of WC in the divertor of fusion reactors. Therefore, we use first-principles calculations to study the hydrogen behavior in WC. The most stable interstitial site for the hydrogen atom is the projection of the octahedral interstitial site on tungsten basal plane, followed by the site near the projection of the octahedral interstitial site on carbon basal plane. The binding energy between two interstitial hydrogen atoms is negative, suggesting that hydrogen itself is not capable of trapping other hydrogen atoms to form a hydrogen molecule. The calculated results on the interaction between hydrogen and vacancy indicate that the hydrogen atom is energetically trapped by vacancy and the hydrogen molecule can not be formed in mono-vacancy. In addition, the hydrogen atom bound to carbon is only found in tungsten vacancy. We also study the migrations of hydrogen in WC and find that the interstitial hydrogen atom prefers to diffusion along the c axis. Our studies on the hydrogen behavior in WC provide some explanations for the experimental results of the thermal desorption process of energetic hydrogen ion implanted into WC.