Preparetion And Thermoelectric Property Study Of Bi₂Te₃-based Alloys Composited Different Second Phases

Bi₂Te₃-based alloys have been the only thermoelectric materials for large-scale commercial applications so far owing to the excellent thermoelectric properties near room temperature.The zT values of both n-type and p-type Bi₂Te₃-based alloys have reached 1.0 at 320 K.The excellent thermoelectric properties have laid a good foundation for its wide application in the field of solid state refrigeration.With the improvement of thermoelectric theory and the development of preparation technology,many methods are proposed to improve the performance of thermoelectric materials.Composition is an execellent method among them.On the one hand it can enhance the scattering of phonons and reduce the lattice thermal conductivity.And on the other hand,it can affect the electrical properties by selecting the appropriate second phase and process.Therefore,it is of great value to do the research on Bi₂Te₃-based alloys composited different second phases.This paper explores the changes in thermoelectric properties of Bi₂?Te,Se?₃-based alloys composited with differnet metal oxides as second phases.We composited Bi₂?Te,Se?₃-based alloys with ZnO,TiO₂,and CeO₂ to improve the thermoelectric performance.In the meantime,we study the electric and thermal transportation differences ofn-type Bi₂?Te,Se?₃-based alloys with different second phases.The main results obtained are listed as blew:1?Different contents of ZnO nanoparticles were compounded into Bi₂Te_2.71Se_0.29alloys by ball milling and hydrolysis method.The effects of different composite processes,different composite contents and different separation methods on the thermoelectric properties of the materials were investigated.Bi₂Te_2.71Se_0.29/ZnO samples were successfully prepared by ball milling and hydrolysis method.It was further found that the samples prepared by ball milling method had lower power factor and higher lattice thermal conductivity,which was due to the unsuitable process and content.Therefore,the thermoelectric performance deteriorated seriously.While as for the samples composited by the hydrolysis method,the Seebeck coefficient was greatly increased due to the energy filtering effect.At the same time,the electrical conductivity remains essentially unchanged,so the power factor was greatly improved.And the lattice thermal conductivity was decreased owing to the composition of ZnO.The sample reached a maximum zT value of 0.68 with 8 mol%ZnO nanoparticles at 450 K.Different separation methods including centrifugation and filtration had a slight impact on the thermoelectric properties,which was mainly because of different density of ZnO and Bi₂Te_2.71Se_0.29 alloys.It could result in the phenomenon of uneven layered distribution,and therefore affected thermoelectric properties.2?TiO₂ was synthesized in situ by the hydrolysis reaction of tetrabutyl titanate,and was successfully composited with Bi₂Se₃.By compositing TiO₂,the carrier concentration was optimized and the intrinsic excitation of the material was suppressed.Therefore,the electrical conductivity was greatly improved.The room temperature power factor was 46%higher than that of Bi₂Se₃ alloys when the TiO₂ content was 10mol%.At the same time,the amorphous TiO₂ enhanced the scattering of phonons,then the lattice thermal conductivity was greatly reduced.Due to the collaborative optimization of thermal and electrical properties,the thermoelectric performance has been greatly improved.When the TiO₂ content was 15 mol%,the maximum zT value reached 0.41 at 525 K,nearly 50%augment over the pristine Bi₂Se₃ binary compound.3?Bi₂Te_2.71Se_0.29/CeO₂ composites were successfully synthesized by ball milling method with different contents of magnetic nanoparticles CeO₂.As the carrier concentration and mobility decreased,the electrical transport performance deteriorated.Therefore,the addition of CeO₂ couldn't improve the electrical transport performance.As the carrier concentration decreased,the electronic thermal conductivity also decreased,which was partially offset by the increase in the lattice thermal conductivity.Finally,the sample had a maximum zT value of 0.71 with 4 vol%CeO₂ nanoparticles at 450 K.