Solid-phase equilibria in the GeBi2Te4-Bi2Te3-Te system and thermodynamic properties of compounds of the GeTe·mBi2Te3 homologous series

The GeBi2Te4-Bi2Te3-Te system was investigated by XRD and EMF measurements of the reversible concentration cell of the type (-) GeTe (solid) │glycerol +KCl │ Ge-Bi-Тe (solid) (+) in the 300-450K temperature range. It was shown that, in the indicated temperature range, elementary tellurium forms tie lines with all telluride phases of the system. Equations for the temperature dependencies of EMF in all phase regions have been obtained from the data of EMF measurements, from which the partial thermodynamic functions of GeTe in alloys have been calculated. The partial molar functions of germanium in alloys were determined by combining obtained data with the thermodynamic functions of GeTe. Standard Gibbs free energy and enthalpy of formation, as well as the standard entropy of the GeBi2Te4, GeBi4Te7, GeBi6Te10 compounds and solid solutions based on Bi2Te3 have been calculated using these data, solid-phase equilibrium diagram of the GeBi2Te4-Bi2Te3-Te system, and corresponding thermodynamic functions of Bi2Te3.