This thesis presents the results of a systematic study on the structural relaxation and the glass transition of ternary metal-metal glasses Zr$ sb{67}$(Ni$ sb{1-x}$Cu$ sb{x}) sb{33}$. Differential scanning calorimetry provides macroscopic evidence of structural changes from the compositional and temperature dependence of enthalpy change. Results from high precision x-ray diffraction and Mossbauer spectroscopy, performed mainly on $ rm Zr sb{67}Ni sb{10}Cu sb{23}$ (x = 0.7), complete the picture of structural changes at the atomic level. Irreversible structural relaxation leads to densification and enthalpy release. Shear-like atomic motion enhances local atomic order, highlighting the atomic processes during the irreversible relaxation. Reversible structural relaxation involves two partly overlapping processes initiated at different temperatures, which are characterized by the solid and liquid atomic mobilities, respectively. Interatomic positional exchanges between Cu and Ni atoms change the local structure and are active during the reversible relaxation at low temperatures, which are also partly responsible for the irreversible relaxation. Above 500 K, shear-like atomic movements characterize the reversible relaxation, involving all three atomic species in a length scale of a few near-neighbor atomic shells. The overall density is unchanged during reversible relaxation. The strong compositional dependence of the glass transition in the ternary glasses indicates an intimate association of the glass transition with interatomic bondings among different atomic species. The atomic motion from room temperature up to above the glass transition temperature, measured by the Mossbauer spectroscopy, is macroscopically tracked by the volume expansion and the enthalpy evolution. The glass transition occurs when the length scale of the atomic motion expands so rapidly that the interatomic potential can no longer maintain the on-site atomic vibration. The rapid development of translational atomic motion upon approaching the glass transition is reflected by the dramatic enhancement of the diffusive atomic motion.

Altounian, Zaven (Supervisor)