Thermal deformation effects on thermoelectric properties for Bi_0.82Sb_0.18alloys

Bi_0.82Sb_0.18alloy bulk materials have been prepared by mechanical alloying followed by a pulsed electric current sintering (PECS) technique. The sintered Bi_0.82Sb_0.18pellets were deformed in the direction perpendicular to applied pressure by a second PECS treatment. Significant decreases of both electrical resistivity and lattice part of the thermal conductivity have been obtained for the deformed alloys. Improved electrical transport properties in deformed Bi_0.82Sb_0.18alloys are attributed to the improvement of bulk density. On the other hand, the lattice part of thermal conductivity is decreased by the deforming treatment. Dislocations and twin domains are formed by the applied deformation. Furthermore the density of the defects is increased with increasing deformation temperature. The lower lattice thermal conductivity is observed in the higher density of defects, which can be one of the reasons for phonon scattering sites. The alloy prepared with deformation treatment at 493 K exhibits a thermoelectric figure of merit ZT of 0.31 at 200 K, improved by a factor about 1.5 by comparison with Bi_0.82Sb_0.18alloy prepared by a conventional single PECS heat treatment.