Solubility of Ti in thermoelectric PbTe compound

For the first time, the temperature dependence of the solubility of Ti in PbTe is considered. The potential of Ti doping in PbTe was recently examined both theoretically and experimentally, in which a similar to 9% efficiency enhancement was observed compared to an undoped PbTe. We present an experimental study of the system for different Ti concentrations indicating the solubility limit of Ti in PbTe and the effect of temperature on the morphology of the alloy. Exceeding the solubility limit leads to phase separation accompanied by formation of the TiTe2 phase. At high temperatures, dissolution of the TiTe2 secondary phase occurs for low Ti concentration, and the system transfers to the single-phase disordered solid solution. On the contrary, for the same temperatures, in the case of higher Ti concentrations the two-phase state is preserved. Theoretical explanation of the observed results is given using ab inito calculations combined with the statistical thermodynamic approach. The quasi-binary PbTe-TiTe2 cross-section of the ternary Pb-Ti-Te phase diagram, indicating the Ti solubility in (Pb1-cTic)Te is presented.