Determination of the thermodynamic potentials of metallic glasses and their relation to the defect structure

We performed calorimetric and shear modulus measurements on four bulk metallic glasses upon heating up to the temperature of the complete crystallization as well as in the fully crystallized state. On the basis of calorimetric experiments, we calculated the excess thermodynamic potentials with respect to the crystalline state - the enthalpy ΔH, entropy ΔS and Gibbs free energy ΔΦ - as functions of temperature. Using high-frequency shear modulus measurements we show that calorimetric determination of ΔH, ΔS and ΔΦ is consistent with the calculation of these potentials within the framework of the interstitialcy theory (IT) within a 15% uncertainty in the worst case for all MGs under investigation. It is concluded that the physical origin of the excess thermodynamic potentials in MGs can be related to a system of interstitial-type defects frozen-in from the liquid state upon melt quenching as suggested by the IT. The estimates of the defect formation enthalpy H f and entropy S f show that H f scales with the shear modulus while S f is quite large (10 k B to 20 k B), in line with the basic assumptions of the IT.