Quantum-mechanical calculations for hydrogen in niobium and tantalum. 2

Results of quantitative theoretical investigations are presented concerning the diffusion coefficients of H and D in Nb and Ta. They are based on the quantum theory of the diffusion of light interstitials and take into account the lattice-configuration dependence of the hydrogen tunneling integrals and the effects of adiabatic saturation of the transition rate. The calculations make use of a semiempirical hydrogen-host-lattice interaction potential which is adapted to experimental data from outside the diffusion phenomena. The resulting theoretical values for the diffusion coefficients agree well with the experimental observations. (author)