Thermodynamic entropy-based parameter of structural disordering and its relation to the width of the X-ray structure factor and defect concentration in a metallic glass

We introduce a new dimensionless thermodynamic parameter α of structural disordering, which is given by the ratio of the excess entropy of glass to its melting entropy. Using calorimetric experiments, we derive this parameter for a Pt-based glass as a function of temperature. Comparing this parameter with literature data on temperature dependences of the width of the X-ray structure factor (FWHM) and the concentration c_def of interstitial-type defects for the same glass, we conclude that above the glass transition temperature T_g there exists a strong correlation between α, FWHM and c_def. This fact implies that macroscopic structural disordering above T_g detected by X-ray diffraction is intrinsically related to structural defects and can be quantitatively characterized by the thermodynamic entropy-based parameter of disordering. The reasons for this interrelationship are briefly discussed.