Temperature-dependent diffusion coefficients fromab initiocomputations: Hydrogen, deuterium, and tritium in nickel

Abstract

The temperature-dependent diffusion coefficients of interstitial hydrogen, deuterium, and tritium in nickel are computed using transition state theory. The coefficient of thermal expansion, the enthalpy and entropy of activation, and the pre-exponential factor of the diffusion coefficient are obtained from ab initio total energy and phonon calculations including the vibrations of all atoms. Numerical results reveal that diffusion between octahedral interstitial sites occurs along an indirect path via the metastable tetrahedral site and that both the migration enthalpy and entropy are strongly temperature dependent. However, the migration enthalpy and entropy are coupled so that the diffusion coefficient is well described by a constant activation energy, i.e., D = D 0 exp͓−Q / ͑RT͔͒, with Q = 45.72, 44.09, and 43.04 kJ/ mol and D 0 = 3.84ϫ 10 −6 , 2.40ϫ 10 −6 , 1.77 ϫ 10 −6 m 2 s −1 for H, D, and T, respectively. The diffusion of deuterium and tritium is computed to be slower than that of hydrogen only at temperatures above 400 K. At lower temperatures, the order is reversed in excellent agreement with experiment. The present approach is applicable to atoms of any mass as it includes the full coupling between the vibrational modes of the diffusing atom with the host lattice.

Phonons calculated from first-principles

“…Heat conductivity depends crucially on the phonon relaxation time [50], which is determined by the anharmonic part of the crystal potential energy. Atomic diffusion can be handle with care when finding the transition state during the hoping process [51].…”

Diffusion Behaviors of Hydrogen Isotopes in Incoloy 800H: A First-Principles Study

“…In recent years, a number of theoretical studies based on first-principles calculations of diffusion mechanisms and behaviors of gas atoms in metal have been published [4][5][6][7][8][9]. Wimmer et al have predicted the temperature-dependent diffusion coefficients of interstitial hydrogen, deuterium, and tritium atoms in nickel [4].…”

“…Wimmer et al have predicted the temperature-dependent diffusion coefficients of interstitial hydrogen, deuterium, and tritium atoms in nickel [4]. Yang et al studied the diffusion behaviors of C, N, and O atoms in V metal [5].…”

First-principles study of temperature-dependent diffusion coefficients: Hydrogen, deuterium, and tritium in α-Ti

“…The reason is that at low temperatures, the zero-point energy effect is more pronounced [7], which increases the jump rate through an exponential dependence, since the energy difference between the transition and ground states shows a reduction trend from hydrogen to its isotopes. As the temperature increases, the zero-point energy effect is offset due to the lower frequencies of isotopes.…”

“…Taking into consideration the importance of diffusion process, many experimental measurements have been performed [1][2][3][4][5][6]. Also, there have been many theoretical efforts to gain diffusion coefficients for multiple materials and the corresponding diffusion mechanisms using fundamental electronic or atomistic approaches [7][8][9][10]. In fact, although the diffusion experiments can determine the overall diffusion coefficients, they cannot generally determine the microscopic physical processes involved in the diffusion steps which are quite important for basic understanding and practical applications.…”