Diffusion in nanocrystalline material

The paper reports on first investigations of the diffusion in nanocrystalline materials. The self-diffusion of the radioisotope 67Cu in nanocrystalline copper has been measured by serial sectioning with the aid of ion-beam sputtering. The values of the diffusion coefficients which were found at 353 K and 393 K are 2×10−18 m2/s and 1.7×10−17 m2/s, respectively, i.e., they are about 16 or 14 orders of magnitude larger than the bulk self-diffusion and about 3 orders of magnitude larger than the grain-boundary self-diffusion in copper. In comparison to the bulk, small values for the activation enthalpy, 0.64 eV, and the pre-exponential factor of the self-diffusion coefficient, 3×10−9 m2/s, have been observed.