Dresden 2003 – scientific programme

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DY: Dynamik und Statistische Physik

DY 11: Fluid dynamics I

DY 11.2: Talk

Monday, March 24, 2003, 10:15–10:30, G\"OR/229

Atomic Dynamics in Liquid NaSn — •Sandro Jahn and Jens-Boie Suck — Materials Research and Liquids, Institute of Physics, Technical University Chemnitz, D-09107 Chemnitz, Germany

In liquid alloys of alkali and post-transition metals like Sn or Pb the TYPE of interaction changes considerably with the relative concentration ot the two elements, thus forming No-dqliquids with competing interactionsNo-dq. By adding more post-transition metal the interaction changes from metallic to ionic and (at 50:50 compsition) to partially covalent with corresponding changes in the electrical properties. We have studied the influence of this change in type of interaction on the atomic dynamics in Na_(100−x)Sn_x with x = 10 to 67 using neutron inelastic scattering at the cold neutron time focusing time-of-flight spectrometer IN6 at the HFR of the Institut Laue-Langevin (Grenoble).

We determined the dispersion relations of the collective excitations from the maxima of the longitudinal current correlation function and the spectrum of the velocity autocorrelation function from the extrapolation (to Q=0) of the dynamic structure factor. Different from the smooth variation of the weighting factors of the 3 partial dynamic structure factors we find a nearly abrupt change of the dispersion, when the liquid enters the region of dominant ionic interaction and a splitting of the dispersion curve in the region of partial covalent interactions. The characteristic frequencies of our experimental results correspond well to recent results from computer simulations.