Variation in entropies of fusion driven by mixing in binary glass forming eutectics

Binary eutectic systems are focused to understand the relationship between the glass formation and thermodynamics. Two molecular eutectic systems are studied and the critical cooling rates for glass formation, enthalpy of mixing Delta H-mix and entropies of fusion Delta S-m are determined at the eutectic compositions. For the systems with positive Delta H-mix, an excess in Delta S-m relative to the linear average of the Delta S-m values of the two pure components is observed, while a deficit in Delta S-m corresponds to negative Delta H-mix. Extended studies of binary metallic eutectics shows similar behaviors, finding that for the alloys with positive Delta H-mix, the excess in Delta S-m at eutectic points reaches an upper limit defined by the ideal mixing entropy. In addition, the deficit in Delta S-m in the binary eutectics is observed to associate with enhanced glass forming ability. The results suggest that the relative Delta S-m variation in eutectics can address effectively the mixing thermodynamics. (C) 2017 Elsevier B.V. All rights reserved.