DIFFUSION IN A CRYSTAL-LATTICE WITH NUCLEAR RESONANT SCATTERING OF SYNCHROTRON-RADIATION

We report on a method for probing the elementary diffusion jumps in cr ystalline lattices on an atomistic scale. The method makes use of sync hrotron 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. Th e acceleration of the decay rate differs for different crystal orienta tions relative to the beam; thus;providing information not only about the rates but also about the directions of the diffusion jumps. As a f irst application we studied the diffusion of Fe-57 in the intermetalli c alloy Fe3Si parallel to the [111] and [113] crystal directions yield ing the diffusion mechanism of iron and its diffusion coefficient. Fro m a comparison with conventional quasielastic Mossbauer spectroscopy t he advantages of the method are deduced. [S0163-1829(98)07317-2].