Dynamics on next-neighbour distances in liquid and undercooled gallium

Abstract

Density fluctuations of liquid and 20 K undercooled gallium have been studied by neutron spectroscopy. The decay of density fluctuations has been recorded at the structure factor maximum over a wide temperature range up to twice the melting temperature. The amplitude of the scattering function falls off with rising temperature in a nonlinear way with a changing slope around 1.5 T melting . The derived generalized longitudinal viscosity shows an upturn with decreasing temperature in the same temperature range. This increase in viscosity can be understood that liquid gallium transforms from a more fluid liquid metal to a more viscous liquid metal in that temperature range upon cooling. The change in the amplitude shows a remarkable agreement with results from liquid aluminium, lead and rubidium. This study suggests a universal crossover in dynamics of liquid monatomic metals, despite the many peculiar properties of gallium.

Slow structural relaxation process facilitates solidification in liquid gallium

“…This change in relaxation times accompanies the changes in the lineshape, evidenced through the lineshape parameter β. We conclude from these results and from the previous observations [28] on the amplitude S(Q 0 , ω = 0) and the generalized longitudinal viscosity η l (Q 0 ) that in the temperature range of 1.2-1.5 T melting the collective dynamics of liquid gallium is altering.…”

“…The rate decreases considerably when the main structure factor peak S(Q 0 ) is reached, the deGennes narrowing. Scattering experiments in the energy domain demonstrated that a fit with a single Lorentzian is a good description of the lineshape at the structure factor maximum [28]. However, measurements with good statistics and a wide dynamic range indicated deviations from the single Lorentzian model [12,13].…”

“…Liquid gallium shows a well-defined deGennes narrowing around the structure factor maximum with a minimum in the linewidth at about Q 0 = 2.45 Å −1 [28]. Figure 1 depicts the intermediate scattering function F(Q 0 , t) of liquid gallium for several temperatures.…”

“…More experimental details can be found in Ref. [28]. Gallium scatters neutrons mainly coherent with a coherent cross section of σ coh = 6.675 barn and an incoherent neutron scattering cross section of σ inc = 0.16 barn [30].…”

“…2469-9950/2020/101(1)/014207 (6) 014207-1 ©2020 American Physical Society More recently, we investigated the dynamics of liquid gallium over a wide temperature range from the undercooled state to twice the melting point, focusing on the gallium dynamics above the melting temperature [28]. Changes in the dynamics at next-neighbor distances were observed in a temperature range of about 1.3-1.5 T m .…”