Optimal Composition Design And Device Assembly Of The Thermoelectric?Bi,Sb?₂?Te,Se?₃ Zone-Melted Inaots For Commercial Applications

(Bi,Sb)2(Te,Se)3 alloys are the best thermoelectric(TE)materials near room temperature and the unique commercially available TE materials up to now.At present,zone-melted(ZM)(Bi,Sb)2(Te,Se)3 oriented polycrystals with better TE properties along in-plane direction are mainly applied for commercial TE devices.The room temperature zTs of p-type and n-type(Bi,Sb)2(Te,Se)3 ZM ingots for solid-state refrigeration are both around 1.0.However,the composition of(Bi,Sb)2(Te,Se)3 ZM ingots for low-temperature power generation has not been optimized yet,resulting in the poor performance of commercial TE devices for power generation.We designed the compositions of(Bi,Sb)2(Te,Se)3 ZM ingots for solid-state refrigeration via point defects manipulation,designed the ZM ingot composition for power generation based on the transition of phase structure,selected ZM ingots with optimized compositions and assembled TE devices for cooling and power generation with commercial processing flow.The main results are as follows:1.Room temperature zT of p-type ingots was improved.Se doping was applied to induce extra point defects and hence the scattering of high-frequency phonons was enhanced.The lattice thermal conductivity of traditional p-type Bio.5Sb1.5Te3+3 wt%Te for refrigeration was effectively decreased and a peak zT?1.2 at 350 K was obtained.Subsequently,decreasing Sb content was adopted to optimize the carrier concentration further and the room temperature zT of the matrix was enhanced to 1.1.In addition,Se/Te alloying is adopted to manipulate the transport of phonons,enhancing the average zT during 300-500 K of p-type Bio.3Sb1.7Te3 ZM ingot for power generation from waste and excess heat.However,Sb doping is not favorable for TE properties of n-type Bi2Te2.7Se0.3 ZM ingot.The dominant role of lost carrier mobility caused by Sb doping deteriorated the TE performance during 300-500 K of n-type Bi2Te2.7Se0.3 ZM ingot.2.The cost of p-type ZM ingot for refrigeration was reduced.Sb alloying was applied to optimize carrier concentration and decrease the lattice thermal conductivity of weak p-type Bi2Te2.7Seo.3 ZM ingot synergistically and a zT?1.0 at room temperature was obtained in Bi0.5Sbi.5Te2.7Se0.3 ZM ingot,which is comparable to that of traditional p-type composition for refrigeration.Meanwhile,the cost of the former is reduced by?20%due to the less content of expensive Sb and Te;The synergistic role of increased carrier concentration and density-of-state effective mass via Sn doping in weak p-type Bi1.8Sb0.2Te2.7Se0.3,contributed to the optimization of room temperature zT and average zT during 300-500 K.3.TE properties of the compositions around phase transition point of Sb2Te3-Sb2Se3 quasi-binary solid solutions were investigated systematically.The lattice thermal conductivity 0.8?1.0 Wm-1K-1 at room temperature of Sb2Te3-xSex(1.5? x ? 2.4)ZM ingots is relatively low.Furthermore,the band degeneracy Nv of Sb2TeSe2 increased possibly according to the calculation of band structure.Through Ag-Sn co-doping,a zT?0.52 at 700 K was obtained in p-type Sb2TeSe2 ZM ingot.4.The on-axis taper of quartz tube is favorable for TE properties of(Bi,Sb)2(Te,Se)3 ZM ingots.The purities of 5N and 4N make no significant effect on TE performance of ingots.The slower the growth rate is,the more time-consuming the ZM process is and the more enhanced the off-stoichiometry is.The large temperature gradient is favorable to prepare high-quality ZM crystals.For p-type Bi0.5Sb1.5Te2.91Se0.09+ 3 wt%Te ZM ingot,the combination of growth condition 25 mm/h+40 K/cm with 4N elements can contribute to excellent TE performance.5.The compositions of(Bi,Sb)2(Te,Se)3 ZM ingots were optimized through adjusting carrier concentration and the zTs at room temperature of both n-type and p-type ZM ingots were enhanced to 1.2.Simultaneously,the average zT during 300-500 K was improved.The TE devices assembled with commercial processing flow,based on the ZM ingots with optimized compositions:the maximum temperature difference is as large as 79 K(hot side temperature is 323 K),which is higher than the like products on the market by 3-5 K;the outpower is 3.75 W when the temperature difference is 160 K with a 5 ? load,which is doubled compared with like products on the market.