ATOMIC TRANSPORT IN AMORPHOUS PD40NI40P20 NEAR THE GLASS-TRANSITION TEMPERATURE - AU DIFFUSIVITY AND VISCOSITY

Measurements of the diffusivity of ion-implanted Au in amorphous Pd40Ni40P20 have been performed at temperatures just below the glass-transition temperature. Concentration profiles before and after annealing were determined with Rutherford-backscattering spectrometry. It is found that the diffusivity in as-quenched material decreases to an equilibrium value presumably due to structural-relaxation processes. The equilibrium values of the diffusivity show a very strong temperature dependence and can be described by D(eq)(T) = 1.7 X 10(17) exp[-(413 kJ/mol)/RT]m2/s. The results have been quantitatively compared to the viscosity of the same material revealing the breakdown of the Stokes-Einstein relation for this metallic glass. This implies the existence of two types of atomic-transport mechanisms in amorphous Pd40Ni40P20. Moreover, from cycling between different equilibrium values of the diffusivity, we found that once amorphous Pd40Ni40P20 has reached a fully relaxed state, the relation between the viscosity and diffusivity is lost.