Defect-induced ordering and disordering in metallic glasses

On the basis of shear modulus measurements on a Pt-based glass, we calculated temperature dependence of the defect concentration c using the Interstitialcy theory. This temperature dependence is compared with temperature dependence of the normalized full width at half maximum (FWHM) γ of the first peak of the structure factor S(q) for the same glass available in the literature. It is found that γ above the glass transition temperature T_g linearly increases with c in the same way for both initial and relaxed (preannealed) samples providing the evidence of defect-induced disordering in the supercooled liquid region independent of glass thermal prehistory. For both states of the samples, the derivative dγ/dc is close to unity. Below T_g, the interrelation between γ and c is entirely different for initial and relaxed samples. In the former case, strong defect-induced ordering upon approaching T_g is observed while relaxed samples do not reveal any clear ordering/disordering. Possible reasons for these observations are discussed. To further investigate the relationship between the normalized FWHM and defect concentration, we performed molecular dynamic simulation of γ(c)-dependence in a high-entropy FeNiCrCoCu model glass. It is found that γ also linearly increases with c while the derivative dγ/dc is again close to unity just as in the case of Pt-based glass.