Structural evolution during the sub-Tg relaxation of hyperquenched metallic glasses

We report the structural characteristics during the sub-T-g relaxation in hyperquenched La55Al25Ni20 glasses. The sub-T-g relaxation is associated with the structural change in intermediate range order, as manifested by the appearance of a prepeak in the x-ray diffraction spectrum. Such structural change could be the source of the Johari-Goldstein relaxation in metallic glasses. The mechanism governing the evolution of the prepeak is different between the glasses with the fictive temperature below 604 K and those above 604 K. Cooperative motion of atoms in La-centered clusters was further discussed in terms of the atomic bond deficiency model. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3447373]