A comprehensive atomistic analysis of the experimental dynamic-mechanical response of a metallic glass

It is shown that assumed anelastic relaxation-time spectra can be recovered reliably from simulated loss-modulus curves that include noise by nonlinear least-squares fitting. The same method is used to obtain spectra for published experimental data on a metallic glass. The results provide a comprehensive kinetic picture of the atomically quantized hierarchy of shear transformation zones (STZs). We resolve a window of STZs consisting of 25-33 atoms, and a simultaneous fit yields the Arrhenius behavior for each size. The corresponding activation energies are 1.75-2.31 eV. The high activation energy that is often observed above Tg is shown to be an artifact of the temperature dependence of the high-frequency shear modulus. The hierarchy of STZ sizes is consistent with both α and β relaxations, suggesting that they originate from the same microscopic mechanism.