Thermodynamic study of the Fe-In-Se system by the electromotive force method

This work presents the results of a study on solid-phase equilibria within the FeSe 2 –FeIn 2 Se 4 –In 2 Se 3 –Se compositional region of the system Fe-In-Se and the thermodynamic properties of FeIn 2 Se 4 and FeSe 2 compounds using X-ray diffraction analysis (XRD), differential thermal analysis (DTA) and electromotive force (EMF) methods. It was established that, at room temperature, this subsystem comprises two three-phase regions: FeSe 2 –FeIn 2 Se 4 –Se and FeIn 2 Se 4 –In 2 Se 3 –Se. Based on the EMF measurement data of concentration cells of the type (-) Fe(s) | glycerol + KCl + FeCl 2 | (Fe in alloy) (+) in the temperature range of 300–450 K, linear equations for the temperature dependence of the EMF were obtained for alloys from the above-mentioned three-phase regions and for the two-phase FeSe + Se alloys. From these data, the relative partial molar thermodynamic functions of iron in these alloys at 298 K were calculated. Based on the phase diagram, equations of virtual cell reactions were established, which allowed the calculation of standard thermodynamic functions of formation (Δ f G°, Δ f H°, Δ f S°) and standard entropies (S°) for the FeSe 2 and FeIn 2 Se 4 compounds. Both thermodynamically characterized compounds are of great practical interest as potential environmentally friendly multifunctional materials possessing magnetic, photovoltaic, optical, and other properties.