Search

The diffusion of Ni and Sn is undesirable in thermoelectric (TE) device. However, the quantitative effect on TE properties is unknown. In this work, the effect of Ni/Sn doping on the TE properties of p-type Bi2Te3 based alloys and the corresponding mechanism are investigated to provide beneficial reference for device designers and researchers. The results show that nickel doping in Bi0.4Sb1.6Te3 can make the intrinsic excitation temperature shift to lower temperature region due to the formation of the second phase NiTe, which greatly reduces the carrier concentration and increases the electrical resistivity. Ultimately, the thermoelectric figure of merit (ZT value) deteriorates rapidly with the increase of Ni content, and only 7 wt ‰ Ni results in a 32% drop in ZT value. Tin doping moves the intrinsic excitation temperature to higher temperature region due to the promotion of Sn’Bi to the generation of anti-sites (Bi’Te and Sb’Te), which significantly increases the carrier concentration and deteriorates the Seebeck coefficient. At last, the ZT value also declines sharply with the increase of Sn content, and just 7 wt ‰ Sn doping results in a 52% drop in ZT value.

Introduction of porous structure is a feasible and promising method for improving thermoelectric performances for thermoelectric materials. Meanwhile, the uniformity of pores distribution plays a decisive role in the objective evaluation of thermoelectric properties for porous structures. In this work, extremely uniform porous structures in p-type Bi0.4Sb1.6Te3 bulks were obtained by pre-mixing with NH4HCO3 combined with resistance pressing sintering (RPS) process. The thermoelectric performance was obviously affected by the porous structure. The increasing porosity resulted in a significant decrease in electrical and thermal conductivity. It was inspiring that the reduction of thermal conductivity could compensate for the deterioration of electrical conductivity, leading to the enhancement in ZT value. The maximum ZT value of 1.11 was obtained for the sample prepared by pre-mixing with 5 ​wt % NH4HCO3 at 343 ​K, which was 20% higher than that of the fully dense sample. Finally, the advantages on the homogeneity of pores, thermoelectric properties and mechanical properties of the sample prepared by this method are confirmed through comparing with the sample prepared without NH4HCO3, when their relative densities both are 90%.