J.-B. Suck

Atomic dynamics of rapidly quenched and annealed nanocrystalline Ni89Hf11

Abstract We investigated the vibrational behaviour of rapidly quenched and annealed nanocrystalline Ni 89 Hf 11 by means of inelastic neutron scattering. From the time-of-flight spectra we determined the generalized vibrational density of states (GVDOS). Using this we calculated the lattice part of the heat capacity. The frequency distribution shows three significant results: First, in reference to the coarser-grained material, the as-quenched nanocrystalline materials show a more enhanced GVDOS at low energies than the annealed ones with almost the same average crystal size. Second, the enhancement is larger the smaller the grain size. Additionally, the energy bands are broadened in case of nanostructured samples.

BRISP, a new small-angle time-of-flight neutron spectrometer to study collective dynamics in disordered matter

An outline is given of the new neutron Brillouin Spectrometer BRISP which was installed during the last years and recently became fully operational at the Institute Laue-Langevin in Grenoble (France). The main technical features are described and some of the first experimental results are presented, demonstrating the present capabilities of this new-type inelastic small-angle spectrometer. Future upgrades are foreseen and expected to further improve the instrument performances.

Temperature dependence of the generalized vibrational density of states of decagonal Al71.5Co13.5Ni15 and its approximant Al71.5Co15.5Ni13

The temperature dependence of the generalized vibrational density of states of decagonal Al71.5Co13.5Ni15 and its approximant Al71.5Co15.5Ni13 has been investigated using neutron inelastic scattering. A shift of the density of states towards lower energies is found with increasing temperature which can be correlated with the expansion of the alloy and the change of the Debye–Waller-factor. Within experimental accuracy, no important difference can be observed between the density of states of the decagonal phase and of its approximant or in their temperature dependence.

Collective atomic dynamics in molten Rb(100−x)Sbx investigated by inelastic neutron scattering

Abstract In molten Rb (100− x ) Sb x a change of binding from pure metallic to ionic and finally covalent can be observed. Here the consequences of this change of the interatomic interactions in the same alloy system on the collective atomic dynamics of Rb 85 Sb 15 and Rb 50 Sb 50 are investigated via the dispersion curves obtained from the dynamic structure factor and the longitudinal current–current correlation function measured by neutron inelastic scattering at 970 K. The change of the dispersion relation on alloy concentration which is observed is discussed.

Vibrational density of states of decagonal Al70Co15Ni15

Abstract The generalized vibrational density of states (GVDOS) has been determined for decagonal Al70Ni15Co15 using cold neutron inelastic scattering techniques. The GVDOS is compared with a computer simulation using realistic binary Al-Co pair potentials and the ‘tiling-and-decoration’ atomic model based on binary tiring with a rhombus edge length of about 6.4 A. It is proposed that the computer modelling of the GVDOS using realistic pair potentials might provide valuable information about the details of the complex atomic structures such as quasicrystals, which are not easily accessed by diffraction experiments. As a first step in this direction, it is shown that the occupancy of certain ‘problematic’ atomic positions in the model can be clearly assigned to particular features of the GVDOS.

BRISP: The New Brillouin Spectrometer at ILL's High Flux Reactor

The new Time-of-Flight (TOF) Brillouin Spectrometer (BRISP) for inelastic neutron scattering has been developed and constructed at ILLs High Flux Reactor (HFR) for investigating a host of open scientific problems in the low-momentum region and relatively high incoming neutron energies with a dedicated instrument [1]. It studies the high-frequency dynamics of atomic nuclei and electron spins in disordered systems, ranging from liquids to compressed gases, including magnetic and biological systems.

Single and collective particle dynamics in liquid Rb80(RbBr)20

The temperature (T) dependence of the single and the collective particle dynamics of a melt containing 80 at% Rb and 20 at% RbBr was investigated using neutron inelastic scattering. Compared to pure liquid Rb, the dispersions obtained from the maxima of the longitudinal current correlation function clearly reflect the change of the atomic interaction from a metallic to a dominantly ionic regime. The T dependence of the atomic dynamics in Rb80(RbBr)20 is characterized by a broadening of the spectra resulting in a shift to higher energies in the dispersion and in the spectrum of the velocity auto-correlation function, which was determined here for a mixture of a liquid metal with a molten salt for the first time.

The order-disorder transition in supersaturated Zr100-xAlx studied by inelastic neutron scattering

Abstract We have studied the influence of supersaturating Zr by Al on the atomic dynamics of the supersaturated solid solution using inelastic neutron scattering before and after the order–disorder transition. The samples ( x =5, 10 and 20 at.%) were characterized by X-ray diffraction and differential scanning calorimetry (DSC). From the neutron scattering data the generalized vibrational density of states (GVDOS), and the dynamic structure factors were determined in all cases. We find a small but distinct weakening of the lower energy (transverse) modes on supersaturation.