For many decades the lead chalcogenides PbTe, PbSe, and PbS (and their solid solutions) have been preferred high-performance thermoelectric materials due to their exceptional electronic and thermal properties as well as great stability during operation. However, there is a lack of understanding about the fundamental relation between the reported high-defect crystal structure containing cation disorder and vacancies and the observed transport properties, which follow expectations for an ideal rock salt crystal structure. Here we have studied a series of undoped lead sulfide samples (Pb 1−x S) with presumed small chemical variations. Crystallographic refinements of high-resolution synchrotron powder X-ray diffraction data give unphysically low lead occupancies (0.75−0.98), in contradiction with the measured charge carrier concentration, resistivity, mobility, and Seebeck coefficient, which show no signs of lead vacancies. A new Rietveld refinement model including preferred orientation parameters and anisotropic strain gives almost full lead occupancy and improved agreement factors. However, transmission electron microscopy analysis reveals that there is no preferred orientation in this system. Instead it is the diffuse scattering due to directional correlated disorder in the structure that necessitates the additional parameters when modeling Bragg intensities. The present approach is a general method for absorbing effects of direction-dependent correlations in advanced materials.

The mixed ionic–electronic conductor β-Zn4Sb3 is a cheap and high-performing thermoelectric material, but under operating conditions with a temperature gradient and a running current, the material decomposes as Zn readily migrates in the structure. Here, we report an improved stability of β-Zn4Sb3 by introducing ion-blocking interfaces of stainless steel to segment the sample, produced by a rapid one-step spark plasma sintering synthesis. The stability of the samples is tested under temperature gradients and electric currents, which reveals significantly improved stability of the segmented samples compared to unsegmented samples. The segmented samples are stable under a temperature gradient from 250 °C to room temperature with no external current, whereas the unsegmented sample decomposes into ZnSb and Zn under the same conditions. The thermoelectric figure of merit, zT, of the segmented sample is slightly reduced, mainly due to the increased thermal conductivity. In conclusion, a rapid one-step synthesis of segmented β-Zn4Sb3 is developed, which successfully improves the long-term operational stability by blocking the Zn ion migration.

The inexpensive and high-performing thermoelectric material β-Zn4Sb3 is a mixed ionic-electronic conductor, which suffers from stability issues due to Zn migration in the structure under thermoelectric operating conditions. Previous ex...

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