First principles DFT analysis on the diffusion kinetics of hydrogen isotopes through bcc iron (Fe): Role of temperature and surface coverage

The diffusion of interstitial H, D, and T in Fe metal at different temperature are evaluated using abinitio density functional theory and transition state theory. The thermal expansion coefficient, Helmholtz free energy of activation, jump factor of diffusion was deter-mined by use of activation energy and phonon calculations. The calculated diffusion coefficient was well described by a constant activation energy, (D = D(0)exp (-Ea)/kT)) with E-a = 0.016, 0.041, and 0.050 eV and D-0 = 1.042 x 10(-7), 0.736 x 10(-7) and 0.572x10(-7) m(2).s(-1 )for H, D, and T, respectively using harmonic transition state theory (hTST) with temperature correction. The calculated permeability and solubility also followed the Arrhenius relation. The earlier experimentally reported higher diffusivity of H atom at lower temperatures than that at higher temperature (200-600 K) was well explained by Wigner + hTST model with temperature correction and semi-classical transition state theory (SC-TST). The present computed results followed the similar trend of experimental findings. Further, the ideal fracture energy was evaluated using the Born-Haber thermodynamic cycle for varied coverage of H, D and T to account for decohesion-based embrittlement. The lighter H atom was seen to cause more decohesion-based embrittlement compared to D and T due to

Automated summary

The diffusion behavior of H, D, and T atoms in Fe metal at different temperatures was analyzed using density functional theory and transition state theory. It was found that lighter H atoms caused more decohesion-based embrittlement compared to D and T.