Phonon scattering by dislocations at grain boundaries in polycrystalline Bi0.5Sb1.5Te3

Reducing lattice thermal conductivity ((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 (l) by dislocation scattering at room temperature and above. In order to closely examine the effect of the dislocation scattering, the (l) of polycrystalline Bi0.5Sb1.5Te3 samples with and without dislocations were measured at low temperature (T<200K). 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 (l) with a theoretical model.