Study On Microstructure And Thermoelectric Properties Of Sn Doped Bi_0.5Sb_1.5Te₃ Alloy

Bi₂Te₃-based materials are mature thermoelectric materials for commercial application at room temperature,but their application fields are limited by the relatively low thermoelectric conversion efficiency of their thermoelectric devices.Therefore,further improve the thermoelectric performance of Bi₂Te₃-based thermoelectric materials and increase their application value to expand the application field are very significance.The thermoelectric performance of Bi₂Te₃-based thermoelectric materials can be improved obviously through the method of element doping and preparation process optimization,which can introduce the impurity level,increase the density of states near Fermi level and the band gap,increase the point defects,grain boundary and dislocations.Therefore,in this article,the optimized Bi_0.5Sb_1.5Te₃ in Bi₂Te₃ base material is taken as the research object,and the following work is done on how to effectively improve its thermoelectric performance:?1?The effects of element doping and intrinsic point defects on the electronic structure of Bi₂Te₃ crystals were studied by first principles calculation.The results show that the impurity level is introduced by Sn atom doping,and the band gap width increased when one Sn atom is added to the cell.The Bi_Te1 inverse defect causes the Fermi energy level to move towards the valence band,and the defect forms energy is lower than V_Te1vacancy defect.The V_Te1 vacancy defect can obviously change the band structure near the Fermi energy level,and increase the band gap,which is beneficial to suppress the intrinsic excitation.?2?Sn element doped Bi_0.5Sb_1.5Te₃ was produced by vacuum smelting method,the experimental results show that Sn element doping formed Sn'_Sb and Sn'_Bi non-equivalent substitution in the material,which increased carrier concentration and inhibited intrinsic excitation.At the same time,dislocation,point defect and lattice distortion were formed in the material,which greatly reduced the lattice thermal conductivity.When the doping amount of Sn element is 0.008(Bi_0.5Sb_1.5Te₃Sn_0.008),the highest ZT value is 1.46,and the average ZT value is up to 1.29.?3?Sn doped Bi_0.5Sb_1.5Te₃ alloy obtained by vacuum smelting process was sintered to SPS,and finally high density block was obtained.The mechanical properties of the samples were improved,and which electrical properties were kept at the same level as those samples produced by vacuum smelting method.However,a large number of dislocations formed in the vacuum smelting process were reduced,which made the scattering phonon ability reduced,so the lattice thermal conductivity was increased.When the Sn doping amount is 0.014(Bi_0.5Sb_1.5Te₃Sn_0.014),the highest ZT is 1.12.?4?Before SPS sintering,a second term was formed in the material through SnTe/PbTe solid solution Bi_0.5Sb_1.5Te₃ alloy,which introduced non-equivalent substitution,increased carrier concentration,effectively improved the electrical and thermal properties,and improved the average ZT value of the whole test temperature region.When the solid solution concentrations of SnTe and PbTe were 0.2wt.%and 0.4wt.%,the average ZT values were 0.88 and 0.95,respectively.