Enhanced thermoelectric performance of Bi85Sb15-graphene composite by modulation carrier transport and density of state effective mass

The Bi-Sb material is regarded as a potential thermoelectric (TE) material for low temperature cooling applications and doping is a commonly used way to modulate the thermoelectric performance of this material. In the present study, graphene (Gr) dopant was introduced into the Bi85Sb15 powder by ball milling and fully densified (Bi85Sb15)1-xGrx (x = 0.0, 0.02, 0.1, 0.5, 1.0 wt%) solid composites were prepared by spark plasma sintering. The scanning electron microscopy and transmission electron microscopy reveal that the inclusion of Gr nanosheets refined the structures, and distributed throughout the grain boundaries and the matrix of the solid Bi-Sb composites, which eventually created more coherent and new interfaces and structural deformities in the matrix of the Bi-Sb alloys. The electric conductivity simultaneously enhanced with Seebeck coefficient, attributed to the increase in carrier concentration and density of state effective mass, respectively. The thermal conductivity is surprisingly increased with graphene doping, especially at high temperature. This is in turning enhanced the TE properties of the (Bi85Sb15)1-xGrx composites, the highest achieved figure of merit, 0.39 (260 K), is obtained for the sample with 0.5 wt% Gr, which is two times larger than that of the pristine sample, 0.18 (280 K). The improvement in TE properties seems to be promising strategy to be followed up for the potential TE materials with Gr doping.