Nuclear magnetic resonance was used, for the first time, to detect slow atomic motion in metallic glasses. In particular, the motion of Be was monitored. It was found that the observations were not consistent with the vacancy-assisted or interstitial diffusion mechanisms, and instead favored the spread-out free-volume fluctuation mechanism for Be diffusion. A comparison with Be diffusion results, as measured by means of elastic back-scattering, also indicated that the energy barriers (1.2eV) to short- and long-range Be motion were the same. The absence of an activation enthalpy distribution was considered to be consistent with the negative values of S/k, which indicated that the thermal fluctuations of spread-out free volume involved a group of atoms. The activation enthalpy distribution was therefore averaged out for Be motion. It was concluded that the 9Be alignment echo technique provided detailed information on the characteristics of Be diffusion.

Slow Atomic Motion in Zr-Ti-Cu-Ni-Be Metallic Glasses Studied by NMR. X.P.Tang, R.Busch, W.L.Johnson, Y.Wu: Physical Review Letters, 1998, 81[24], 5358-61