Temperature-dependent monovacancy diffusion in tungsten: Bridging the gap between experiment and theory

Tungsten, a key plasma-facing material for fusion reactors, exhibits self-diffusion behavior that deviates from the simple Arrhenius kinetics. Experiments suggest that monovacancy-mediated diffusion dominates below ∼2400 K; however, theoretical diffusivities overestimate measurements by up to two orders of magnitude. Here, we reconcile this discrepancy through first-principles calculations that explicitly incorporate temperature-dependent effects, including the lattice thermal expansion and vibrational free energy. We found that the vacancy formation energy increases quadratically with temperature, primarily due to vibrational contributions at high temperatures, while the migration barrier remains nearly constant. The resulting diffusion coefficients closely agree with the experimental data in the range 1700–2400 K. Moreover, despite the strong temperature dependence of the activation energy and pre-exponential factor, their variation satisfies a Meyer–Neldel-type compensation relationship, preserving an overall Arrhenius-form for diffusivity. Our results demonstrate that below ∼2400 K, self-diffusion in tungsten is governed by monovacancy-mediated atomic migration, whereas above this threshold, enhanced diffusion might arise from collective atomic mechanisms. These findings resolve a long-standing theory–experiment discrepancy and provide essential input for modeling the microstructural evolution in fusion reactor environments.