Nuclear resonant Bragg scattering: Measurement of self-diffusion in intermetallics (original) (raw)

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

Physical Review B

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 57 Fe in the intermetallic alloy Fe 3 Si parallel to the ͓111͔ and ͓113͔ crystal directions yielding the diffusion mechanism of iron and its diffusion coefficient. From a comparison with conventional quasielastic Mössbauer spectroscopy the advantages of the method are deduced. ͓S0163-1829͑98͒07317-2͔

Diffusion in solids studied by nuclear resonant X-ray and neutron scattering

Journal of Synchrotron Radiation, 2002

Nuclear resonant scattering of synchrotron radiation and quasielastic neutron scattering allow the measurement of frequencies, directions and lengths of jumps of diffusing atoms. Both methods have been successfully applied to diffusion in solids. Synergies and respective advantages of these two techniques as well as recent developments are discussed on the basis of an example: diffusion in intermetallic alloys.

Diffusion in crystalline materials

1999

Recently nuclear scattering of synchrotron radiation proved to be a powerful new method to study the elementary diffusion jump in crystalline solids. The scattered radiation decays faster when atoms move on the time scale of the excited-state lifetime of a Mössbauer isotope because of a loss of coherence. The acceleration of the decay rate differs for different crystal orientations relative to the beam providing information not only about the rates but also about the directions of the elementary jumps. We discuss first applications of the method.

Enhanced iron self-diffusion in the near-surface region investigated by nuclear resonant scattering

Surface Science, 2002

The access to X-rays of third generation synchrotron radiation sources enables studies of dynamics in metallic systems in grazing incidence geometry. Combining grazing incidence reflection of X-rays with nuclear resonant scattering of synchrotron radiation allows depth-selective investigations of hyperfine parameters and diffusion phenomena of iron and iron compounds. The unique feature of this method is its sensitivity to near-surface motions of atoms and not exclusively to the atoms on the surface. The depth sensitivity can be varied between about two and more than 10 nm. A 300 nm thick 57 Fe sample grown by molecular beam epitaxy on a cleaved MgO(0 0 1) substrate was investigated. The diffusion coefficient of iron in the near-surface layer (thickness about 2 nm) is almost two orders of magnitude larger than in bulk bcc iron at the same temperature.

Time-domain interferometry using synchrotron radiation applied to diffusion in ordered alloys

The European Physical Journal B, 2001

Time-domain interferometry of synchrotron radiation (TDI) has recently been used as a tool for investigating diffusion in glasses. This work deals with an extension of this technique to ordered structures. In a TDI experiment performed on the B2 alloy CoGa at the APS the intensity scattered into Bragg directions showed no detectable quasielastic signal. Experimental lower limits of the elastic contribution are given. They are in accordance with the coherent scattering function derived in this paper. This result indicates that TDI can be applied to diffusion in crystalline solids, e.g. intermetallic alloys, by using diffuse scattering. Requirements and limitations of diffuse scattering experiments are discussed.

Fe diffusion in amorphous and nanocrystalline alloys studied using nuclear resonance reflectivity

Physical Review B, 2005

It is demonstrated that nuclear resonance reflectivity from isotopic multilayers can be used as a sensitive technique to study self-diffusion of a Mössbauer isotope ͑ 57 Fe in the present case͒. In the case of isotopic multilayers, in which alternate layers have the same chemical composition and differ only in the abundance of 57 Fe, nuclear resonance scattering causes x-ray scattering contrast between adjacent layers, resulting in the appearance of Bragg peaks corresponding to the bilayer periodicity. Diffusion of 57 Fe across the isotopic interface results in a decrease in the scattering contrast and thus a decrease in the intensity of the Bragg peak, making it possible to measure diffusion lengths of the order of 0.1 nm in chemically homogeneous films. The technique has been used to study self-diffusion of Fe in amorphous FeZr and nanocrystalline FeN alloys. In a-FeZr, measurements yield activation energy for Fe diffusion E = 0.42± 0.05 eV and the pre-exponent factor D 0 = exp͑−39± 1͒ m 2 / s. In nanocrystalline Fe 60 N 40 , variation in diffusivity due to structural relaxation at temperatures as low as 393 K could be observed. Measurements in the structurally relaxed state yield E = 0.8± 0.2 eV and D 0 = exp͑−28± 4͒ m 2 /s.

Quasielastic scattering of synchrotron radiation from non-resonant atoms

Hyperfine …, 2000

The beat pattern produced by nuclear resonant scattering of synchrotron radiation scattered from two stainless steel foils in constant relative motion has been measured at 3-ID beamline at the Advanced Photon Source. Contrary to theoretical prediction and different from the result in glassy material, the scattering in Bragg directions from single crystal of CoGa diffusional smoothening of the quantum beats was absent within the statistical errors.

Synchrotron radiation study of diffusion in FeAl

Hyperfine Interactions, 1998

Nuclear resonance scattering of synchrotron radiation has been used to determine the elementary diffusion jump in the ordered stoichiometric alloy FeAl. To that aim the intensity decay in forward direction is measured as a function of crystal orientation. A decision between various jump models confirms earlier results from classical quasielastic Mössbauer spectroscopy, but with considerably better angular resolution.

Self-diffusion in nanoscale structures measured by neutron reflectometry

Journal of Phase Equilibria and Diffusion, 2005

Neutron reflectometry (NR) is an attractive tool for probing self-diffusion on a nanometerlength scale. The depth resolution available with NR is in the subnanometer range, which is due to contrast among the isotopes of an element, and NR provides a unique opportunity to probe self-diffusion in nanometer-range structures. Self-diffusion measurements in FeZr amorphous and nanocrystalline chemically homogeneous multilayers of type [Fe 100-x Zr x / 57 Fe 100-x Zr x ] 10 , were performed using neutron reflectivity. On the basis of the results obtained, the self-diffusion mechanism in nanometer-range structures is discussed in this article.