Study Of Mid-temperature Expand And Anisotropy For Bi₂Te₃-based Thermoelectric Materials

Bismuth telluride (Bi2Te3) based bulk materials have been the best commercial TE materials with high zT values of～1 near room temperature, and are mainly used in the solid state refrigeration.Further zT valves optimization and effective adjustment of peak zT temperature, making it suitable for mid-temperature power generations, are the main objective of (Bi,Sb)2(Te,Se)3 alloys in the past few years. This work adopts powder hot pressure molding and hot deformation technique, and optimizes chemical coompositions based on band gap and carrier concentrations to optimize the zT values and peak zT temperature of (Bi,Sb)2(Te,Se)3 alloys; prepare block materials though various methods to sdudy the anisotropy of different kinds of (Bi,Sb)2(Te,Se)3 alloys. The main results are listed as below:1. We successfully shifted the maximum zT values of n-type bismuth telluride-based alloys to relatively high temperatures (approximately 600K) by Se-alloying and SbI3 doping. The detrimental effects of minority carriers on the Seebeck coefficient and thermal conductivity were suppressed as a result of increases in both the band gap and electron concentration. At last, high-performance bismuth telluride-based alloys were fabricated utilizing the repetitive HD method. As a consequence of these factors, the HD3-0.001SbI3+Bi2Tei.9Se1.1 materials, showed a maximum zT of～1.1 at approximately 600K and the largest average zTav of 0.9 in the range of 300-650K. These data indicate significant promise for these materials in mid-temperature power generation.2. We studied the effect of S alloying on Sb2Te3 based alloys’thermoelectric performance. It shows that S alloying did not improve the Seebeck as parper before reported, however, it do reduce the lattice thermal conductivity and optimize the zT valves of Sb2Te3 based alloys.3. We prepared a large bulk of n-type Bi2Te2.3Seo.7 alloy-700 g to repeat the high performance obtained from the samples with small sizes by powder hot pressure molding and hot deformation technique. The property measurement shows that the thermoelectric properties of different parts from the massive bulk show 28% differences, and the maximum valvue of zT reache 1.15. In addition, it is aslo found that the Bi2Te2.3Seo.69 alloy prepared by HP and HD can match the properties of commercial zone-melted materials, what more, the large bulk materials have better mechanical properties, which greatly improve the processing performance of the materials4. We prepared block materials though various methods to sdudy the anisotropy of different kinds of (Bi,Sb)2(Te,Se)3 alloys to sduty the influence of various molding methods on the anisotropy of materials. We apply different precess on commercial zone-melted materials and measurement the thermoelectric performance and mechanical properties of different directions of the bulk materials.