Preparation And Thermoelectric Properties Of Single Element Doped Bismuth Telluride Based Aiioy

Bismuth telluride-based alloys are the most widely used TE materials near room temperature for many years.The maximum ZT value of commercial Bi₂Te₃-based alloys is about 1.0 at nearly room temperature,and Bi₂Te₃-based alloys are widely used in room temperature thermoelectric cooling.In recent years,with the increasing demand for low-quality waste heat recovery in the medium-low temperature region?400K⁶00K?,the research of Bi₂Te₃-based alloys have once again become a hot spot in the field of thermoelectricity.However,the traditional commercial Bi₂Te₃-based alloys can not be used for heat recovery in the low-temperature range because the value of ZT decreases greatly when the temperature is above 400K.In this paper,the p-type Bi_0.5Sb_1.5Te₃Pb_X and n-type Bi₂Se_0.3Te_2.7In_X alloys were prepared by melting method combined with Spark Plasma Sintering technology by doping Pb and In elements in Bi₂Te₃-based alloys.By optimizing the chemical composition of the alloy and adjusting the carrier concentration and microstructure,the power factor can be effectively increased,the lattice thermal conductivity can be reduced,and the bipolar effect can be suppressed.As a result,the ZT value of Bi₂Te₃-based alloy can be increased and the temperature range of high ZT can be widened.The main work and results are as follows:?1?The phonon scattering and thermal conductivity of Bi_0.5Sb_1.5Te₃Pb_X alloy prepared by melting were enhanced by introducingbP _S?_b andbS _T?_e point defect,dislocations,nano Te and PbTe phases.Pb doping effectively increases carrier concentration,increases power factor and strongly inhibits bipolar effect.As a result,not only the ZT value of the material is increased,but also the temperature range of high ZT value is widened.At 423K,Bi_0.5Sb_1.5Te₃Pb_0.008 obtains the highest ZT value of 1.34.In the test temperature range of323K⁵23K,the total value of ZT remains above 0.8,and the average ZT value is 1.1.The ZT is above 1 in the wide temperature range of 180K from 343K to 523K.?2?Bi_0.5Sb_1.5Te₃Pb_X alloys with dense grains were prepared by melting,grinding and SPS sintering.Compared with smelting samples,the carrier concentration of SPS sintered samples decreases,carrier mobility increases and power factor increases slightly,while the lattice thermal conductivity and bipolar thermal conductivity increase slightly with the disappearance of Te phase.The ZT value of Bi_0.5Sb_1.5Te₃Pb_0.008 sintered by SPS is 1.2 at403K,and the average ZT is 1.01 at 300K-523K.?3?After ball milling and SPS sintering,the grain size and thermal conductivity of the melted Bi_0.5Sb_1.5Te₃Pb_0.008 samples decreased.The maximum ZT value of the sample is 1.32at 363K after 20 hours ball milling,which is 10%higher than that of the sample sintered directly by SPS without ball milling.?4?In was successfully doped into Bi₂Se_0.3Te_2.7 matrix to form solid solution alloy,which increased carrier concentration,increased power factor,enhanced phonon scattering and decreased lattice thermal conductivity.At 443 K,the highest value of ZT of Bi₂Se_0.3Te_2.7In_0.034 is 0.74,which is 27%higher than that of undoped Bi₂Se_0.3Te_2.7.