A thermodynamic approach to indium-enriched Se-Te-Sn alloy systems

Differential scanning calorimetry (DSC) has been used to study phase transformations of glassy-ceramic sample Se78-xTe20Sn2Inx (x = 0, 2, 4, 6) alloys under nonisothermal conditions and determine various thermodynamic parameters. The effect of the Indium additive in Se–Te–Sn glasses has been observed through specific heat (ΔCp) measurements. The value of ΔCp is maximum and minimum for Se72Te20Sn2In6 and Se78Te20Sn2, i.e. 0.0249 and 0.006 kJ/kg֩C. These measurements have also been used to assess several thermodynamic quantities as a function of temperature, including the Gibbs free energy difference (ΔG), entropy difference (ΔS), and enthalpy difference (ΔH) between the undercooled melt and the corresponding equilibrium solid phases. The values of ΔSgc, ΔHgc, and ΔGgc are maximum for Se72Te20Sn2In6, i.e. 0.297, 12.3, and −3.3 J/g֩C respectively, and minimum for Se78Te20Sn2, i.e. 0.063, 3.6, and −0.28 J/g֩C respectively. The values of Cp after glass transition (Cpe) and below glass transition temperature (Cpg) have also been discovered to be strongly composition-dependent. We observed two new correlations: one reveals the linear variation in the logarithm of the change in specific heat (ΔCp) with the logarithm of the heating rate (i.e., log i), and the other shows the linear variation between the Δ(dα/dT) and the logarithm of the heating rate (i.e., log β). The S, G, Cp, and H curves obey the realistic physical relations that are thermodynamically consistent for a second-order phase transition, as defined by Ehrenfest. The Gibbs energy function, on the other hand, has an inflexion point at the transition temperature.