MECHANICAL INSTABILITIES IN EXTENDED SOLID-SOLUTIONS NEAR THE CRYSTAL-TO-GLASS TRANSITION

In order to study the change in elastic properties near the crystal-to-glass transition in extended solid solutions, we measured the low-temperature specific heat of rapidly quenched crystalline NbPd (0 less-than-or-equal-to x(Pd) less-than-or-equal-to 0.52) and ball-milled ZrAl (0 less-than-or-equal-to x(Al) less-than-or-equal-to 0.5) far from equilibrium. The results show in both cases a drastic decrease in the Debye temperature prior to structural transformations (i.e. b.c.c. --> f.c.c. for crystalline NbPd at x(Pd) almost-equal-to 0.44 and h.c.p. --> amorphous for ZrAl at x(Al) almost-equal-to 0.2), indicating a large elastic softening as a precursor of an underlying mechanical instability. We demonstrate that the extracted shear moduli of the rapidly quenched and ball-milled samples agree well with recent molecular dynamics simulations and emphasize the crucial role of elastic shear softening for the stability of the crystalline phase.