Temperature dependence of collective modes in liquid sodium

Pilgrim, W.‐C.; Hosokawa, Shinya; Saggau, H.; Sinn, H.; Burkel, E.

doi:10.1016/s0022-3093(99)00218-5

Cited by 94 publications

(91 citation statements)

References 13 publications

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“…Concerning the polycrystal, two excitations with predominantly longitudinal and transverse polarization are well visible for q > 0.3 Å −1 . The spectra corresponding to the liquid phase are similar to previously published data (18,19) and appear clearly broader than for the polycrystal. For what concerns the polycrystal, the presence of transverse excitations for q values well within the first Brillouin zone in a spectrum that corresponds to the dynamic structure factor Sðq;ωÞ and that as such probes the longitudinal dynamics, might result at first sight surprising.…”

Section: Resultssupporting

confidence: 86%

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Fingerprints of order and disorder on the high-frequency dynamics of liquids

Giordano

Monaco

2010

Proc. Natl. Acad. Sci. U.S.A.

119

133

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It is largely accepted that liquids are characterized by a short-range order usually corresponding to that of the solid phase at the same density. It is less clear to what extent dynamic properties of liquids and crystals can be compared. In particular, high-frequency collective excitations reminiscent of phonons in solids exist as well in liquids. They are however traditionally discussed in terms of relaxation processes characteristic of the liquid phase. We report here on a quantitative comparison of the collective excitations in liquid and polycrystalline sodium. We show that liquid sodium exhibits acoustic excitations of both longitudinal and transverse polarization at frequencies strictly related to those of the corresponding crystal. The only relevant difference between the liquid and the polycrystal appears in the broadening of the excitations: An additional disorder-induced contribution comes into play in the case of the liquid, which we show to be related to the distribution of local structures around the average one. These results establish a direct connection between structural and dynamic properties of liquids, with shortrange order and overall structural disorder leaving very specific fingerprints.vibrational dynamics | X-ray scattering T he short-range order in liquids, characterized by parameters like, e.g., the first neighbors distance and number, is usually similar to that of the corresponding solids (1, 2). Ab initio calculations of liquid structures spanning a large density range do support this idea (3). For what concerns dynamic properties, the situation is more complex. Local vibrations appear in the liquid as in the corresponding solid, although they are usually much broader (1). This broadening is generally related to the distribution of local structures that is present in the liquid phase (4) and that is, e.g., characterized by the distribution of first neighbors distances. Collective excitations exist as well in liquids, and their broadening is usually attributed to relaxation processes (5-7). In fact, the response of a crystal to an external perturbation can be formally expressed in terms of phonons, the modes of lattice vibration that can be defined in presence of a long-range, periodic structure. In liquids this description is instead formally not appropriate, and the concept of relaxation is usually introduced with reference to a dynamic process that controls the reequilibration of the system after it has been perturbed (8). Several distinct relaxation processes can be introduced to describe the dynamics of liquids, each one characterized by a characteristic time, τ, that sets the timescale over which it is active and observable. Indeed, if the perturbation frequency, ω, is such that ωτ ≪ 1, the relaxation is active, whereas when ωτ ≫ 1 the relaxation process does not have the time to take place and is frozen. In the infinite frequency limit, where all relaxations are frozen, the liquid behaves like a solid: This limit corresponds to the elastic regime, where only the instantaneous ...

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Section: Resultssupporting

confidence: 86%

“…For this reason, we decided to study the highfrequency acoustic excitations of the simplest liquid metal, sodium. Despite the several studies carried out on this prototypical system (17)(18)(19), a systematic comparison of the results for the liquid and the crystal is still missing.…”

mentioning

confidence: 99%

Fingerprints of order and disorder on the high-frequency dynamics of liquids

Giordano

Monaco

2010

Proc. Natl. Acad. Sci. U.S.A.

119

133

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“…In this picture, Frenkel realized that a liquid should maintain solid-like shear waves, similarly to those existing in a solid, at all frequencies ω larger than 1 τ [2]. This prediction was later confirmed experimentally [17][18][19][20][21]. Longitudinal waves, associated with density fluctuations, are considered to be unaffected in this picture, apart from different dissipation laws for ω < 1 τ and ω > 1 τ [2].…”

Section: Harmonic Theorymentioning

confidence: 97%

Liquid heat capacity in the approach from the solid state: Anharmonic theory

Bolmatov

Trachenko

2011

Phys. Rev. B

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Calculating liquid energy and heat capacity in general form is an open problem in condensed matter physics. We develop a recent approach to liquids from the solid state by accounting for the contribution of anharmonicity and thermal expansion to liquid energy and heat capacity. We subsequently compare theoretical predictions to the experiments results of 5 commonly discussed liquids, and find a good agreement with no free fitting parameters. We discuss and compare the proposed theory to previous approaches.

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“…for an earlier and a more recent review on the dynamics of liquid metals see [1,2]. Liquid alkali metals have been studied in particular, because they show distinct inelastic excitations [3][4][5][6][7]. One common finding was the upward bending of the frequency dispersion above the values expected from hydrodynamics, which is called positive dispersion.…”

Section: Introductionmentioning

confidence: 99%

“…One of the few studies explored the changes of the collective excitations with temperature in liquid sodium up to the boiling point in four coarse temperature steps [6]. Further investigations on changes in the dynamics with rising temperature up to the boiling point and beyond focused on the self-diffusion of liquid alkali metals and the underlying changes in the dynamics with decreasing density [8].…”

Section: Introductionmentioning

confidence: 99%

Experimental evidence for two different dynamical regimes in liquid rubidium

Demmel

Morkel

2017

EPJ Web Conf.

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Abstract. We present evidence for changes in the dynamics of liquid rubidium with rising temperature. The thermal expansion of this liquid alkali metal shows a changing derivative with temperature in a temperature range of about 400-500 K. With neutron scattering the amplitude at the structure factor maximum demonstrates a changing slope with increasing temperature. A derived averaged structural relaxation time can be understood that an additional relaxation process sets in upon cooling. The deduced generalized viscosity and high frequency shear modulus indicate a change in dynamics in the same temperature range. All these findings point to a change in dynamics of the equilibrium liquid metal state with a dynamical crossover from a viscous to a fluid-like liquid metal well above the melting point.

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Temperature dependence of collective modes in liquid sodium

Cited by 94 publications

References 13 publications

Fingerprints of order and disorder on the high-frequency dynamics of liquids

Fingerprints of order and disorder on the high-frequency dynamics of liquids

Liquid heat capacity in the approach from the solid state: Anharmonic theory

Experimental evidence for two different dynamical regimes in liquid rubidium

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