Microscopic Dynamics of Liquid Aluminum Oxide

Abstract

Collective excitations have been observed in liquid aluminum oxide at high temperatures by combining a containerless sample environment with inelastic x-ray scattering. The excitation spectra show a well-defined triplet peak structure at lower wave vectors Q (1 to 6 nanometers-1) and a single quasi-elastic peak at higher Q. The high-Q spectra are well described by kinetic theory. The low-Q spectra require a frequency-dependent viscosity and provide previously unknown experimental constraints on the behavior of liquids at the interface between atomistic and continuum theory.

Structure and dynamics in liquid alumina: Simulations with an ab initio interaction potential

“…The shear viscosity η, calculated from the time-correlation function of the stress tensor, is (32±4)mPa⋅s at 2350K. The corresponding kinematic viscosity η l =4/3η+η V (η V being the bulk viscosity) is (80±4)mPa⋅s, which justifies the assumption η≈η V made in [13], although η V seems to be slightly larger than η.…”

“…In Ref. [13] the authors show that applying hydrodynamic theory to fit the x-ray S(Q,ω) yields viscosities much smaller than the macroscopic ones. One possible approach to explain the strong damping of the collective modes is to generalize hydrodynamics by introducing frequency-dependent transport coefficients.…”

“…A dynamic correlation function that is accessible in inelastic scattering experiments is the dynamic structure factor S(Q,ω) [13], i.e. the spectrum of the time-correlation function of particle density fluctuations.…”

“…This study is motivated by recent container-less experiments in which both the static [11,12] and the dynamic [13] structure factors were measured using x-ray and neutron scattering techniques. We will demonstrate that the potential gives the experimentally reported liquid density at zero pressure and reproduces both static and dynamics structure factors extremely well.…”

High-pressure studies with x-rays using diamond anvil cells

“…The pair distribution function, extracted from XRD or EXAFS, is often used for structural description [60,178,195,380] and directly compared to theory and simulation results. The dynamical x-ray structure factor, often obtained from IXS and nuclear scattering, provides information on collective excitations in liquids and glasses [381]. X-ray imaging enables the measurement of material properties including density [76,327,328] and viscosity (e.g., [158]) in liquids.…”