Thermoelectric performance of graphene composited BiSbTe bulks by high pressure synthesis

Abstract

Polycrystalline Bi0.4Sb1.6Te3 bulks composited with various graphene content (x = 0, 0.02, 0.05, and 0.1 wt%) were fabricated by high-pressure-and-high-temperature (HPHT) synthesis and high pressure sintering at 4 GPa. The samples by HPHT exhibit the morphology of the large-size well-crystallized lamellar grain. After high pressure sintering, the random distributed grains with smaller size are obtained. Plenty of nanograins and lattice structural disorders are generated by quenching from melt under high pressure. The graphene dispersion reveals inverse effect on thermoelectric properties, due to the competing factors of doping effect and interface scattering. With a low content (≤0.05 wt%), graphene addition shows doping effect and phonon scattering, which results in the reduction of Seebeck coefficient, electrical resistivity, and lattice thermal conductivity. However, this trend is reversed as the graphene content continuously increases to x = 0.1 wt%. Therefore, the doping effect disappears, generating increased Seebeck coefficient and electrical resistivity. Meanwhile, the lattice thermal conductivity seems to be enhanced by volume effect, but it is still lower than that of the pristine sample. Compared to the maximum ZT of 1.09 at 423 K for the pristine sample, a maximum ZT of 1.26 at 423 K is obtained and the thermoelectric performance is enhanced in temperature range of 323–500 K for Bi0.4Sb1.6Te3 sample with 0.05 wt% graphene.