Phase separation and nanostructuring in the thermoelectric material PbTe1-xSx

The average and local structures of the (PbTe) 1 − x (PbS) x system of thermoelectric materials has been studied using the Rietveld and atomic pair distribution function (PDF) methods. Samples with 0 . 25 ≤ x are macroscopically phase separated. Phase separation was suppressed in a quenched x = 0 . 5 sample which, nonetheless, exhibited a partial spinodal decomposition. The promising thermoelectric material with x = 0 . 16 showed intermediate behavior. Combining TEM and bulk scattering data suggests that the sample is a mixture of PbTe rich material and a partially spinodally decomposed phase similar to the quenched 50% sample. This results in a nano-meter scale inhomogeneous material that accounts for its very low thermal conductivity.