Hydrogen in $\alpha$-iron: stress and diffusion

TL;DR

This study uses density-functional theory to analyze how hydrogen atoms interact with alpha-iron, revealing how concentration and stress influence absorption sites, lattice distortion, and diffusion rates.

Contribution

It provides detailed insights into hydrogen absorption sites, lattice distortions, and diffusion barriers in alpha-iron under various conditions, using first-principles calculations.

Findings

Hydrogen prefers octahedral sites at high concentrations causing lattice distortion.

Hydrogen diffuses faster in distorted lattices, with diffusion rates increasing by about 30% under stress.

External stresses alter diffusion barriers by approximately 10%.

Abstract

First-principles density-functional theory has been used to investigate equilibrium geometries, total energies, and diffusion barriers for H as an interstitial impurity absorbed in $\alpha$-Fe. Internal strains/stresses upon hydrogen absorption are a crucial factor to understand preferred absorption sites and diffusion. For high concentrations, H absorbs near the octahedral site favoring a large tetragonal distortion of the BCC lattice. For low concentration, H absorbs near the tetrahedral site minimizing the elastic energy stored on nearby cells. Diffusion paths depend on the concentration regime too; hydrogen diffuses about ten times faster in the distorted BCT lattice. External stresses of several GPa modify barriers by $\approx$ 10%, and diffusion rates by $\approx$ 30%.