Understanding the mechanism that connects heat transport with crystal structures and order/disorder phenomena is crucial to develop materials with ultra-low thermal conductivity (k), for thermoelectric and thermal barriers applications. Researchers from CRISMAT laboratory synthesized the n-type sulfide CuPbBi5S9 with ultra-low k of 0.6-0.4 in the temperature range 300-700 K. In contrast to prior studies, we show that this synthetic sulfide does not exhibit the ordered gladite mineral structure but instead a copper-deficient partially disordered aikinite structure with Bi replacing Pb, according to the chemical formula Cu1/3☐2/3Pb1/3Bi5/3S3. By combining experiments and lattice dynamics calculations, we elucidated that the ultra-low k of this compound is a result of combined structural disorder induced by the processing method and very low energy optical modes associated with Pb and Bi ions and, to a smaller extent, Cu. This vibrational complexity at low energy hints to substantial anharmonic effects that contributes to enhance phonon scattering. Importantly, we show that this aikinite-type series Cu1-x☐xPb1-xBi1+xS3 provide an interesting structural prototype for engineering n-type thermoelectric sulfides by controlling disorder and optimizing doping.
This work was done in collaboration with chemists, physicists and theoreticians from France (CRISMAT, ISCR, IJL), UK (University of Reading), China (Chongqing University) and USA (Central Michigan University).
Journal of the American Chemical Society, https://doi.org/10.1021/jacs.1c11998
Contact : Emmanuel Guilmeau