Solubility and microstructure in the pseudo-binary PbTe–Ag2Te system

The solvus lines of the PbTe and Ag2Te phases in the pseudo-binary PbTe–Ag2Te system have been determined using diffusion couples and unidirectional solidification by the Bridgman method. The solubilities of both Ag2Te in PbTe and PbTe in Ag2Te decrease with decrease in temperature. For the former, this change is from 14.9 at% Ag (694 °C) to 0.5 at% Ag (375 °C), while for the latter it is from 12.4 at% Pb (650 °C) to 3.1 at% Pb (375 °C). The decrease in solubilities leads to the formation of precipitates of Ag2Te in PbTe and PbTe in Ag2Te. In particular, fast atomic diffusion in Ag2Te results in the precipitation of PbTe even in quenched samples. From the temperature dependence of these solubilities, heats of solution have been determined. In the diffusion couple, the phase boundary moves toward PbTe. In the region between the phase boundary and the initial interface, PbTe transforms to β-Ag2Te (cubic) retaining the cube-on-cube orientation relationship.