Self Diffusion in Liquid Titanium: Quasielastic Neutron Scattering and Molecular Dynamics Simulation

摘要

Self diffusion in liquid titanium was measured at 2000 K by quasielastic neutron scattering (QNS) in combination with container less processing via electromagnetic levitation. At small wavenumbers q the quasielastic signal is dominated by incoherent scattering. Up to about 1.2 A~(-1) the width of the quasielastic line exhibits a q~2 dependence as expected for long range atomic transport, thus allowing to measure the self diffusion coefficient D_(Ti) As a result the value D_(Ti) = (5.3 ± 0.2) × 10~(-9) m~2s~(-1) was obtained. With a molecular dynamics (MD) computer simulation using an embedded atom model (EAM) for Ti, the self diffusion coefficient is determined from the mean square displacement as well as from the decay of the incoherent intermediate scattering function at different q. By comparing both methods, we show that the hydrodynamic prediction of a q~2 dependence indeed extends up to about 1.2 A~(-1). Since this result does not depend significantly on the details of the interatomic potential, our findings show that accurate values of self diffusion coefficients in liquid metals can be measured by QNS on an absolute scale.