The measurement of self-diffusion coefficients in liquid metals with quasielastic neutron scattering

Abstract

Abstract. Quasielastic incoherent neutron scattering (QENS) has proven to be a versatile tool to study self diffusion of atoms in liquid metals. Here it is shown, that coherent contributions to the signal in the small q limit appear as a flat and energy independent constant to the QENS signal in single-component liquid metals even for systems with a small incoherent scattering cross section, like aluminum. Container-less processing via electromagnetic or electrostatic levitation devices, especially designed for QENS, enables the in-situ measurement on liquid metallic droplets of sizes between 5 mm to 10 mm in diameter. This gives access to the study of chemically reactive, refractory metallic melts and extends the accessible temperature range to undercoolings of several hundred Kelvin below the respective melting point. Compared to experiments using a thin-walled crucible giving hollow-cylindrical sample geometry it is shown that multiple scattering on levitated droplets is negligible for the analysis of the self-diffusion coefficient. QENS results of liquid germanium and 73 germanium isotope mixtures, titanium, nickel, copper and aluminum are reviewed. The self-diffusion coefficients of these systems are best described by an Arrhenius-type temperature dependence around their respective melting points.

Active learning of uniformly accurate interatomic potentials for materials simulation

“…m Ref. [56], D = 7.2 × 10 −9 m 2 /s at 980K and 7.9 × 10 −9 m 2 /s at 1020K. cost of FF simulations.…”

Atomistics of self-diffusion in liquid metals

“…In comparison, there is also an activated formalism [5] suggested qualitatively by J. Frenkel [31] and generally observed in measurements [6,18,19], see Figure 1(b), which results in lnD~1/T, i.e.…”

“…Besides measurements under microgravity, quasielastic neutron scattering (QENS) [14][15][16][17][18][19] was argued to probe "the dynamics on atomic length scales and on a picosecond time scale, short enough to be undisturbed by the presence of convective flow." [18] "In order to derive the self-diffusion coefficient from QENS one has to assume that concepts developed in the framework of hydrodyanmics [20], i.e.…”

“…[18] "In order to derive the self-diffusion coefficient from QENS one has to assume that concepts developed in the framework of hydrodyanmics [20], i.e. in the limit of small wavenumber q values, are valid also at q values accessible by QENS" [18] and the self-diffusion coefficient was then related to the width of the QENS signal [18,21].…”

Self-diffusion in single-component Yukawa fluids

“…Except the two extreme cases of Cu (D R ;0.040) and Zn (D R ;0.027) all the other data are scattered in a rather narrow range (D R ;0.032±0.03). Moreover, using a more recent value for the self-diffusion in Cu melt (3.27×10 −5 cm 2 s −1 according to [46]) we obtain D R ;0.033, which also belongs to the specified range. Similar relationships for the reduced coefficient of self- diffusion in liquid metals at the melting temperature were proposed in [47,48] on the basis of quite different arguments.…”