Quantum diffusion of hydrogen isotopes in copper

The quantum diffusion of H, D, T and μ+ in copper is studied. The impurity-host configurational interaction is evaluated according to the prescriptions of Teichler. The impurity is represented as a Gaussian wave packet and the total transition probability is evaluated explicitly at low, high and intermediate temperature across a piecewise quadratic potential barrier. it is found that the tunnelling transitions dominate at low temperatures while over-barrier transitions dominate at high temperatures. The characteristic transition temperature for μ+ in Cu is found to be in good agreement with the experimental value. The O-T-O diffusion path is adopted for H, D and T and the O-O path for μ+ diffusion. The contribution of excited states in the respective potential wells is also included. The calculated pre-exponential factors D0 and migration energies Esub(m) are found to be in good agreement with the experimental values wherever available. An inverse isotope dependence in D0 and Esub(m) is found above T = 250 K while it is absent at low temperatures. D0 and Esub(m) are also reported for the intermediate temperature range. (author)