First-principles study of temperature-dependent diffusion coefficients for helium in $\alpha$-Ti

TL;DR

This study predicts how helium diffuses in alpha-titanium at various temperatures using first-principles calculations, revealing anisotropic diffusion behavior and the impact of helium dimers on diffusion pathways.

Contribution

It introduces a comprehensive first-principles approach to calculate temperature-dependent helium diffusion coefficients in alpha-titanium, including vibrational coupling and energy pathway analysis.

Findings

Diffusion is faster in the xy plane than along the z axis.

Helium dimers at octahedral sites reduce energy barriers.

Diffusion coefficients increase with temperature.

Abstract

The temperature-dependent diffusion coefficients of interstitial helium atom in $\alpha$-Ti are predicted using the transition state theory. The microscopic parameters in the pre-factor and activation energy of the impurity diffusion coefficients are obtained from first-principles total energy and phonon calculations including the full coupling between the vibrational modes of the diffusing atom and the host lattice. The climbing image nudged elastic band (CINEB) method is used to search for the minimum energy pathways and associated saddle point structures. It is demonstrated that the diffusion coefficients within the \emph{xy} plane ($D_{xy}$) is always higher than that along the \emph{z} axis ($D_{z}$), showing remarkable anisotropy. Also, it is found that the formation of helium dimer centered at the octahedral site reduces the total energy and confines the diffusion of helium atoms.