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

Abstract

Differential scanning calorimetry (DSC) has been used to study phase transformations of glassy-ceramic sample Se_78-xTe₂₀Sn₂In_x (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 (ΔC_p) measurements. The value of ΔC_p 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 ΔS_gc, ΔH_gc, and ΔG_gc 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 C_p after glass transition (C_pe) and below glass transition temperature (C_pg) 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 (ΔC_p) 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, C_p, 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.