NEUTRON BRILLOUIN-SCATTERING AND LIQUID METAL-MOLTEN SALT MIXTURES

The dispersion of collective density fluctuations (extended sound modes) has been measured in mixtures of liquid alkali metals and the corresponding molten alkali-halide salts. Mixtures with salt concentrations from 10 to 40% were investigated for momentum transfers Q between 4 and 14 nm-1. For Q-values larger than 11 nm-1 the collective modes could even in the most favourable case no longer be separated from the quasi-elastic peak, the width of which increases roughly ∼Q 2 in this region of momentum transfers. At a concentration of 10% RbCl in Rb we find a dispersion which would correspond to expanded liquid Rb at the temperature of the mixture (∼1000 K), demonstrating the dominant metallic character of the mixture (screening by nearly free electrons) at this salt concentration. At higher concentrations of salt, where influences from different partial dynamic structure factors interplay, the dispersions deviate from this simple structured dispersion curve, most likely due to the influence of an early onset of some ionic type of screening in the liquid. © 1990 Società Italiana di Fisica.