Phase separation and nanostructuring in the thermoelectric material PbTe1-x Sx studied using the atomic pair distribution function technique

The average and local structures of the ${(\text{PbTe})}_{1\ensuremath{-}x}{(\text{PbS})}_{x}$ system of thermoelectric materials has been studied using the Rietveld and atomic pair distribution function methods. Samples with $0.25\ensuremath{\le}x$ 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 confirms that, in the bulk, this sample is inhomogeneous on a nanometer length scale, which may account for its enhanced thermoelectric figure of merit.