Evidence of Defect-Mediated Zirconium Self-Diffusion in AmorphousCo92Zr8

Abstract

We have measured the pressure dependence of 95 Zr self-diffusion in structurally relaxed Co 92 Zr 8 glass at 698 K. The resulting activation volume of ͑0.9 6 0.1͒V, where V is the mean atomic volume, is similar to vacancy diffusion in crystalline solids. This suggests that, while Co does not diffuse via thermal defects in Co-rich Co-Zr glasses [P. Klugkist et al., Phys. Rev. Lett. 80, 3288 (1998)], Zr selfdiffusion is mediated by vacancylike defects. We thus provide evidence of the existence of an opposite Kirkendall effect in interdiffusion between certain amorphous alloys as proposed by K. N. Tu and T. C.

Diffusion and viscous flow in bulk glass forming alloys

“…Molecular dynamics simulations suggest a connection between the low-frequency excitations in glasses observed at low temperatures and collective long-range diffusion at elevated temperatures. Only for large atoms, vacancy-like defects seem to play a role [20] and may give rise to an opposite Kirkendall effect [21]. Vacancy-like defects may also enhance diffusion in as quenched metallic glasses prior to structural relaxation [9] although this effect is not seen in all systems [10].…”

Nucleation and growth in bulk metallic glass under high pressure investigated using in situ x-ray diffraction

“…14 For simplifying the analysis, we assume that there is only homogeneous nucleation in the alloys. From the classic nucleation theory, the pressure effect on the nucleation activation energy, ⌬G* can be expressed as: 15 ‫ץ/)*‪(⌬G‬ץ͓‬ P͔ϭϪ(32 3 /3)͓⌬V/(⌬G) 3 ͔, where is interfacial energy, and ⌬GϭG a ϪG c is the free energy difference between the amorphous state, G a and crystalline state G c , ⌬GϾ0. ⌬VϭV a ϪV c is the difference of molar volume between amorphous phase V a and crystalline phase V c .…”

Thermal-vacancy-assisted phase transition in FePt thin films

“…Activation volumes of atomic diffusions in solids are usually determined from tracer diffusion measurements at pressures, in which the diffusivity D is constant over an experimental series at a single temperature and pressure. [10][11][12] However, for a structural transition, the tracer diffusivity D varies with time at a given temperature and pressure, and thus this conventional method cannot be employed to yield the activation volume in this case. Here, by employing kinetic studies on the pressure dependence of rate constants of ordering parameter variations, we measured the activation volume of the L1 0 -ordering transition in FePt thin films.…”