Phonon scattering by dislocations at grain boundaries in polycrystalline Bi_0.5Sb_1.5Te₃

Reducing lattice thermal conductivity (κ_l) of a thermoelectric material is one of the most popular strategies to improve its thermoelectric performance. Particularly, many efforts have been focused on decreasing grain size to effectively scatter low-frequency phonons by boundary scattering. In addition to the boundary scattering, we have recently demonstrated that dense arrays of dislocations formed in grain boundaries can further reduce the κ_l by dislocation scattering at room temperature and above. In order to closely examine the effect of the dislocation scattering, the κ_l of polycrystalline Bi_0.5Sb_1.5Te₃ samples with and without dislocations were measured at low temperature (T < 200 K). Because other phonon scattering mechanisms like Umklapp and point-defect scatterings are not dominant at low temperature, we clearly show the presence of the dislocation scattering in the sample with the dislocations by successfully describing its low temperature experimental κ_l with a theoretical model.