Solubility of YbTe in Sb2Te3 and thermodynamic properties of the solid solution

The solubility of YbTe in Sb2Te3 is investigated by a combination of DTA, XRD, SEM, and EMF methods. The fragment of the T–x phase diagram of the YbTe–Sb2Te3 system is constructed for 0–25 mol.% YbTe. It is shown that the solubility limit for YbTe in Sb2Te3 is achieved at 15 mol.% YbTe at 300 K and at 17.5 mol.% YbTe at 855 K. From the EMF measurements with an YbTe electrode the partial thermodynamic functions of the YbTe pseudo-component are calculated for the alloys of different compositions. Also, the standard integral thermodynamic functions of the YbTe dissolution in Sb2Te3 as well as the standard thermodynamic functions of formation and the standard entropy of the solid solution are calculated from the experimental data.

► Up to 15 mol.% YbTe is soluble in Sb2Te3 forming the β-phase, which retains the structure of Sb2Te3.
► Partial relative thermodynamic functions of YbTe in the β-phase and thermodynamic functions of dissolution of YbTe in Sb2Te3 are obtained from the EMF measurements.
► The standard Gibbs free energy and enthalpy of formation of the β-phase are negative and show an increase of the absolute value with increasing the YbTe content, whereas the standard entropy shows an opposite trend.