Diffusion in a crystal lattice with nuclear resonant scattering of synchrotron radiation

We report on a method for probing the elementary diffusion jumps in crystalline lattices on an atomistic scale. The method makes use of synchrotron radiation coherently scattered in the forward direction after nuclear resonant excitation. The decay of forward-scattered radiation is faster ("diffusionally accelerated") when atoms move on the time scale of the excited-state Lifetime because of a loss of coherence. The acceleration of the decay rate differs for different crystal orientations relative to the beam; thus;providing information not only about the rates but also about the directions of the diffusion jumps. As a first application we studied the diffusion of Fe-57 in the intermetallic alloy Fe3Si parallel to the [111] and [113] crystal directions yielding the diffusion mechanism of iron and its diffusion coefficient. From a comparison with conventional quasielastic Mossbauer spectroscopy the advantages of the method are deduced. [S0163-1829(98)07317-2].