Measurements of the atomic diffusion of Be were made at temperatures ranging from 530 to 710K. Below the glass transition temperature of about 625K, the data suggested that single atomic jump Be diffusion occurred with a migration enthalpy of about 1eV/atom in both alloys. At temperatures below the glass transition temperature, the Be diffusivity in Zr46.7Be27.5Ti8.3Cu7.5Ni10 (figure 10) was an order of magnitude higher than that in Zr41.2Be22.5Ti13.8Cu12.5Ni10. This was attributed to the larger fraction of free volume in the former alloy. At temperatures above the glass transition, the temperature dependence of the Be diffusivity increased in both alloys, with apparent activation energies of 4.5eV/atom in Zr41.2Be22.5Ti13.8Cu12.5Ni10 and 1.9eV/atom in Zr46.7Be27.5Ti8.3Cu7.5Ni10. By taking account of the change in configurational entropy due to the glass transition, the Be diffusion mechanism in the supercooled liquid states of the alloys were explained in terms of single atomic jumps in a continuously changing configuration of neighboring atoms. The corresponding migration enthalpies were the same as in the solid states, and the larger activation energies above the glass transition were explained by the increase in configurational entropy with temperature, which was smaller in Zr46.7Be27.5Ti8.3Cu7.5Ni10 than in Zr41.2Be22.5Ti13.8Cu12.5Ni10. A comparison of the Be diffusivity and viscosity of Zr46.7Be27.5Ti8.3Cu7.5Ni10 above the glass transition revealed a breakdown of the Stokes-Einstein relationship; thus indicating the operation of cooperative processes in the supercooled liquid state.

U.Geyer, S.Schneider, Y.Qiu, M.P.Macht, T.A.Tombrello, W.L.Johnson: Materials Science Forum, 1997, 235-238, 343-8