Fabrication and thermoelectric properties of c-axis-aligned Bi0.5Sb1.5Te3 with a high magnetic field

We simultaneously investigated the effects of nanostructure and crystal alignment on the thermoelectric performance of polycrystalline Bi0.5Sb1.5Te3. An appropriate experimental procedure was devised for a sequential process of slip-casting under a 6 T magnetic field for c-axis alignment and the use of a spark plasma sinter machine for sintering. Flake-shaped powders with particles less than 36 μm in diameter stacked up with c-axis alignment under a 6 T rotating magnetic field, while the same powders with particles less than 5 μm in diameter showed a random orientation with no magnetic field. The c-axis-aligned material under the magnetic field showed an increase in hole mobility along the direction perpendicular to the c-axis that resulted in a 15% decrease in the electric resistivity, while the Seebeck coefficient and thermal conductivity remained unchanged; thus the figure of merit was improved by 15%. Theoretical evaluation of the electrical resistivity according to the c-axis alignment showed good agreement with the experimental results.