THE CALORIMETRIC GLASS-TRANSITION OF AMORPHOUS PD40NI40P20

The calorimetric glass transition in amorphous Pd40Ni40P20 was measured in a series of Differential Scanning Calorimetry (DSC) experiments. Especially the exact shape and position of the glass-transition peak were examined after different pre-annealing treatments of the sample and at different heating rates. The experimental results are in good agreement with a kinetic model of the glass transition. In particular, we found strong support for the existence of an equilibrium state when amorphous Pd40Ni40P20 is heated above its glass transition, and derived that the shape and position of glass-transition peak of amorphous Pd40Ni40P20 at a given heating rate depends on a single structure parameter, in this paper designated as the average amount of free volume. The kinetics of free-volume changes are fully in agreement with results from viscosity measurements and speed-of-sound measurements. In order to obtain a good agreement between the model calculations and the experimental DSC curves, heat effects from chemical ordering were included in the calculations and the thermal delay of the measurement device was modelled with a simple RC-model.