Experimental evidence for two different dynamical regimes in liquid rubidium

Demmel, F.; Morkel, C.

doi:10.1051/epjconf/201715102002

Cited by 3 publications

(2 citation statements)

References 29 publications

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“…The correlations of the stress tensor fluctuations decrease strongly in a temperature range up to about 500 K and then change the gradient. In the same temperature range the correlated fluctuations of volume and entropy, represented through the thermal expansion coefficient, increase strongly [60], and above 500 K the increase of the thermal expansion coefficient changes distinctly to a quite modest value. Both macroscopic parameters indicate through their changes of fluctuations a change in dynamics in the liquid.…”

Section: Resultsmentioning

confidence: 93%

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Stokes-Einstein relation of the liquid metal rubidium and its relationship to changes in the microscopic dynamics with increasing temperature

Demmel

Tani

2018

Phys. Rev. E

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For liquid rubidium the Stokes-Einstein (SE) relation is well fulfilled near the melting point with an effective hydrodynamic diameter, which agrees well with a value from structural investigations. A wealth of thermodynamic and microscopic data exists for a wide range of temperatures for liquid rubidium and hence it represents a good test bed to challenge the SE relation with rising temperature from an experimental point of view. We performed classical molecular dynamics simulations to complement the existing experimental data using a pseudopotential, which describes perfectly the structure and dynamics of liquid rubidium. The derived SE relation from combining experimental shear viscosity data with simulated diffusion coefficients reveals a weak violation at about 1.3T_{melting}≈400 K. The microscopic relaxation dynamics on nearest neighbor distances from neutron spectroscopy demonstrate distinct changes in the amplitude with rising temperature. The derived average relaxation time for density fluctuations on this length scale shows a non-Arrhenius behavior, with a slope change around 1.5T_{melting}≈450 K. Combining the simulated macroscopic self-diffusion coefficient with that microscopic average relaxation time, a distinct violation of the SE relation in the same temperature range can be demonstrated. One can conclude that the changes in the collective dynamics, a mirror of the correlated movements of the particles, are at the origin for the violation of the SE relation. The changes in the dynamics can be understood as a transition from a more viscous liquid metal to a more fluid-like liquid above the crossover temperature range of 1.3-1.5 T_{melting}. The decay of the amplitude of density fluctuations in liquid aluminium, lead, and rubidium demonstrates a remarkable agreement and points to a universal thermal crossover in the dynamics of liquid metals.

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Section: Resultsmentioning

confidence: 93%

“…The temperature dependence of the density is directly related to the thermal expansion coefficient. The thermal expansion coefficient of liquid rubidium shows an identical change with rising temperature at about 450 K [60]. The shear viscosity η can be represented through the stress tensor autocorrelation function [4,15]:…”

Section: Resultsmentioning

confidence: 99%

Stokes-Einstein relation of the liquid metal rubidium and its relationship to changes in the microscopic dynamics with increasing temperature

Demmel

Tani

2018

Phys. Rev. E

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Revealing mechanism of non-Arrhenius viscosity change in metal melts based on Wulff cluster model

Shao

Lin

et al. 2023

Scripta Materialia

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Dynamics on next-neighbour distances in liquid and undercooled gallium

Demmel

2018

J. Phys.: Condens. Matter

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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.

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Experimental evidence for two different dynamical regimes in liquid rubidium

Cited by 3 publications

References 29 publications

Stokes-Einstein relation of the liquid metal rubidium and its relationship to changes in the microscopic dynamics with increasing temperature

Stokes-Einstein relation of the liquid metal rubidium and its relationship to changes in the microscopic dynamics with increasing temperature

Revealing mechanism of non-Arrhenius viscosity change in metal melts based on Wulff cluster model

Dynamics on next-neighbour distances in liquid and undercooled gallium

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