Standard Thermodynamic Functions of Sb2Te3-Rich Germanium Antimony Tellurides: EMF Measurements

The GeSb₂Te₄–Sb₂Te₃–Te system was investigated in the temperature range of 300–450 K using X-ray diffraction (XRD) and electromotive force (EMF) measurements on reversible galvanic cells of the type: (−) GeTe (solid) │ glycerol + KCl (electrolyte) │ Ge–Sb–Te (solid) (+). The results indicate that, within the studied temperature range, elemental tellurium establishes tie lines with all telluride phases present in the system. Based on the EMF measurement data, linear equations describing the temperature dependence of the electromotive force for electrode alloys corresponding to different phase regions of the system were established. These equations were used to calculate the partial thermodynamic functions of GeTe in the alloys. By combining the obtained data with the integral thermodynamic functions of GeTe, the partial molar functions of germanium in the alloys were calculated. Based on these data and the solid-phase equilibrium diagram of the GeSb₂Te₄–Sb₂Te₃–Te system, as well as corresponding thermodynamic functions of Sb₂Te₃, the standard Gibbs free energy of formation, enthalpy of formation, and standard entropy of GeSb₂Te₄, GeSb₄Te₇, GeSb₆Te₁₀, and Sb₂Te₃-based solid solutions were calculated.