Thermodynamics of Te₈₀Ge_{20 − x} Pb_x glass-forming alloys

The specific heat of liquid and solid phases and the heats of crystallization and fusion have been measured by differential scanning calorimetry (DSC) for a series of Te₈₀Ge_{20 − x} Pb_x alloys (0≤x≤20). The enthalpy, entropy, and free energy of the undercooled liquid are quantitatively assessed with reference to the crystal phases. The available formulas for computing the free energy of the liquid are compared, and their relative merits are discussed. The glass transition temperature is shown to depend strongly on the ratio of the average excess specific heat of the liquid to the entropy of fusion. An anomaly in the liquid specific heat, which is particularly important for Te₈₀Ge₂₀ and Te₈₀Ge₁₅Pb₅, leads to very good glass forming ability for these alloys; this is demonstrated by preparing amorphous samples by means of fluxing.