First Observation of Quantum Diffusion in Non-Cubic Metal: Deuterium Diffusion in In

Abstract

Diffusion of deuterium in indium is studied herein. In the temperature range 200–350 К, mass transfer is controlled predominantly by the mechanism of overbarrier atomic jumps; at temperatures from 80 to 120 К, by tunneling; whereas in the range from 120 to 200 К, there takes place a gradual transition from one migration mechanism to the other. These results are of fundamental significance since it is shown for the first time that quantum diffusion can be observed in a metal with a crystal lattice other than the body centered cubic one. Conditions are specified that are necessary for the observation of quantum diffusion of hydrogen: low values of Debye temperature, density of atomic packing in the lattice, and distance between the nearest equilibrium positions of hydrogen atoms. Moreover, data on the influence of point defects on hydrogen tunneling in solids are gained for the first time as well. The quantum diffusion coefficient is twice as high in the sample with enhanced vacancy concentration.

Strong Increase of Tunneling Rate of Hydrogen in Indium in the Presence of Vacancies

“…The influence of vacancies on the quantum diffusion coefficients D was investigated at temperatures from 77 to 125 K. In this range, the deuterium diffusion in indium was effected by the quantum migration mechanism. 8 Besides, in indium, at temperatures from 13 to 100 K, vacancies induced by irradiation or plastic deformation are dominating point defects, 28 while above 100 K, they are virtually absent. In the course of investigation, the quantum diffusion coefficients determined for the specimens with significantly different concentrations of radiation defects were compared, and the type of defects affecting D was specified.…”

“…Experiments were carried out using two modes of the accelerating technique of nuclear reactions and the technique of isochronous annealings. The D 1 values, i.e., for a high concentration of radiation defects, were determined by the online technique of nuclear reactions, NRAOL. ,, In this case, the D measurements are performed upon continuous irradiation of a specimen with deuterons, and in this mode, the concentration of defects increases with time, which makes it possible to obtain the D values for specimens containing radiation defects. The NRAOL technique is briefly described in Section ; earlier it was applied for measuring the coefficients of classical and quantum diffusion of deuterium in sodium, potassium, and indium. ,, …”

“…This result is common for the cases of application of the NRAOL technique at low temperature: for deuterium diffusion in sodium, 3 potassium, 4 and indium. 8 Equation 1 is a solution of the Fick equation for diffusion of an impurity into a plate with a thickness x 0 and a constant concentration c* at the plate surface. This means that, upon a continuous irradiation of the specimens with deuterons, at low temperatures, the deuteride of a metal is formed at a depth x ≥ x 0 , which is an internal source of the deuterium diffusion in the specimens.…”

“…17−27 With the above in mind, the task of the work was set on the experimental investigation of the influence of vacancies on the coefficients of quantum diffusion of hydrogen in metals. It was favored by the lately obtained results for the system indium− deuterium, first of all, data on the overlapping temperature ranges in which deuterium tunneling was observed 8 and predomination of vacancies in the subsystem of point defects in the material. 28 The application of the techniques of nuclear reactions, NRAs, for measuring the deuterium diffusion coefficients was highly successful.…”

“…Diffusion in solids is governed by two mechanisms: tunneling and overbarrier jumps; yet, the data on classical diffusion predominate, whereas the quantum diffusion was investigated only for hydrogen isotopes at low temperatures. − As for the classical diffusion, one of the main scientific interests is focusing on the experiments related to the vacancy impact on the diffusion coefficients. Such experiments present information about the concentration and types of point defects in crystals and energy barriers for atomic migration in the crystal lattice.…”