Microstructure And Thermoelectric Properties Of Sb₂Te₃-based Semiconductors

Thermoelectric efficiency is determined by the figure of merit and temperature gradient between hot and cold junctions.Hence,as the continuous development of new materials and the upsurge in ZT values provide the material support for the development of TE devices,constructing larger temperature gradient between hot and cold junctions is also indispensable.However,one sole material can hardly possess high ZT values at broad temperature ranges,therefore a segmented device consisting of one more type TE materials with high ZT values and different optimum temperature might be the possible solution to maintain a high efficiency across a large temperature gradient.In this paper,Acceptor doping and enlarging the band gap was used to enhance the figure of merit and expand the temperature range with high ZT of Bi_0.5Sb_1.5Te₃ and Sb₂Te₃.The effect of Mg acceptor doping for the microstructure and thermoelectric properties of Bi_0.5Sb_1.5Te₃ and In-Mg doping for Sb₂Te₃ was studied systematically.Finally,the performance of segmented TE power-generating device which based on Mg doping Bi_0.5Sb_1.5Te₃ and In-Mg doping Sb₂Te₃ was calculated.The main results are listed as below:Alkaline-earth metal magnesium（Mg）is chosen as acceptor dopant to tailor the thermoelectric transport parameter of Bi_0.5Sb_1.5Te₃ compounds which are fabricated by high energy ball mill and spark plasma sintering（SPS）.Mg doping could effectively increase the carrier concentration and thus enhance the electrical conductivity,in addition it also decreased the lattice and thermal conductivity,which cooperatively enhances the figure of merit.As a result,a high ZT_aveve of¹.24 from 300 to 480 K was obtained for Mg0.01Bi0.5Sb1.49Te3 sample.In Ⅴ-Ⅵ compounds,p-type Sb₂Te₃-based thermoelectric materials may behave better for mid-temperature power generation due to larger band gap（E_g=0.2 eV）,and In doping could further enlarge the bang gap to push its'optimum temperature above 300℃.Then,Mg acceptor doping was used to compromise the impaired electrical transport properties,as well as further suppress the detrimental bipolar conduction.These combined effects resulted in a peak ZT of 0.96 at 680 K for Mg_0.025In_0.1Sb_1.875Te₃materials,indicating a great potential for application in mid-temperature thermoelectric power generation.In the end,thermoelectric analysis was performed on p-type single-stage thermoelectric generator which combined with Mg_0.01Bi_0.5Sb_1.49Te₃ and Mg_0.02In_0.1Sb_1.88Te₃ by the finite element method.300 K⁶80 K is loaded as temperature difference.Simulation result shown thatη_max=12.6%and P_max=1.55 W/cm² when J=0.36A/cm² and J=0.44 A/cm² respectively.