QUASI-ELASTIC NEUTRON-SCATTERING IN LIQUID CA0.4K0.6(NO3)(1.4)

Time-of-flight measurements have been performed on the ionic system Ca 0.4K0.6(NO3)(1.4) in the equilibrium liquid phase, in order to determi ne the temperature and wavenumber dependences of the quasielastic line width. The quasielastic neutron scattering has been examined by convo luting the resolution function with three different models, Lorentzian , Lorentzian raised to the power 2/3 (a good approximation for a Kohlr ausch line shape with beta approximate to 0.7), and two Lorentzians. T he results show a line shape incompatible with a single Lorentzian for m. The Kohlrausch line width shows a marked deviation from the Dq(2) b ehaviour expected in the incoherent approximation. Analogous deviation s arise for the narrower main contribution from the two-lorentzian mod el. Both of these models can be interpreted qualitatively in terms of mode-coupling theories, but the experimental results show no clear dis tinction between them, or even between them and more complex models. T hus no meaningful quantitative comparison to theory can be obtained, a n ambiguity which is endemic for studies of glass phenomena.