Investigation of self-diffusion in nanocrystalline copper by NMR.

Self-diffusion in nanostructured crystalline copper (average crystal size 10 nm) was investigated by studing the rotating-frame nuclear magnetic relaxation time T1rho of 63Cu as a function of temperature between 283 and 425 K. Above about 350 K an atomic motion-induced relaxation was observed. An activation enthalpy of 0.69 eV was deduced for the corresponding difusion process. This activation enthalpy is about 30 percent smaller than the activation enthalpy for grain boundary diffusion in copper bicrystalls.