Evidence of diffusion via collective hopping in metallic supercooled liquids and glasses

Abstract

We report on measurements of the mass dependence ͑isotope effect E͒ of Co diffusion in both the glassy as well as the supercooled liquid states in a Pd 40 Cu 30 Ni 10 P 20 glass. The isotope effect, which is a fingerprint of the diffusion mechanism, is very small ͑Ͻ0.1͒ in both states, suggesting diffusion via highly collective hopping. In particular, E does not change upon isothermal relaxation from the glassy into the supercooled liquid state. Our results lend strong support to the view that even after macroscopic softening of a glass the underlying atomic transport mechanism is still solidlike thermally activated hopping in a considerable temperature range above the caloric glass transition temperature.

Atomic transport in dense multicomponent metallic liquids

“…For comparison 57 Co tracer diffusion in Pd43Ni10Cu27P20 (Ref. [44]) and diffusivities calculated from viscosity η of liquid Pd40Ni10Cu30P20 (Ref. [21]) via the Stokes-Einstein relation (Eq.…”

“…Consequently transport coefficients can continuously be measured from the equilibrium liquid down to the conventional glass transition temperature T g . Figure 10 displays diffusivities in viscous PdNiCuP alloys from Co tracer diffusion measurements, that cover more than 13 decades [25,44], derived from the mean relaxation times and from viscosity [19,21] calculated via Stokes-Einstein (Eq. 10).…”

Interdiffusion in amorphous AlxZr1-x alloys

“…The lower value for the activation enthalpy (1.3 eV) for interdiffusion in the partially crystallised multilayers of specimen series 2 may be explained by interdiffusion governing grain-boundary diffusion in the nanocrystallised Alrich sublayers. Even though the diffusion mechanisms in grain boundaries 100 and the amorphous phase [23][24][25] are expected to be closely related, 101 the associated activation enthalpies might be different, in particular, because of a distinct difference in the (excess) free volume (see what follows). The orientation-averaged activation enthalpy for grain-boundary self-diffusion, Q gb , correlates with the excess free volume in the grain boundary.…”

“…It is expected that a cooperative movement of atoms, [23][24][25] in which groups of more than, say, ten atoms participate in a chain-like displacement for one resulting diffusion event, i.e., a net atomic jump, 26 is the prevailing mechanism for diffusion in metallic glasses. However, the direct exchange of a single atom with a vacancy-like defect may also play a role in binary zirconium-based amorphous alloys.…”

Properties of Bulk Metallic Glasses

“…При более высоких температурах скорость коллективной диффузии атомов (вначале никеля и, вероятно, меди) стано-вится сравнимой с таковой для единичных атомов [19]. Это объясняется тем, что, например при Т = = 650 К, никель имеет значительно более высокий коэффициент диффузии в Zr (D ~ 10 -18 м 2 /с), чем алюминий (D ~ 5·10 -20 м 2 /с), и следовательно, вре-мя коллективного сдвига для атомов Ni становится сопоставимым со временем диффузии отдельных атомов.…”