WILEY Its latest open access (OA) Flagship magazine Small Science Recently published from Dresden University of Technology Vladimir Lesnyak Professor of the latest work of the research group , Reported that the Bi-Te-Se Compound heterostructure nanosheets enhance Bi2Te3 Thermoelectric properties of base materials . As the only thermoelectric material in commercial application at present , The one-step synthesis method proposed in this paper can realize nanostructure and solve the problem of multi-step synthesis in this system , So as to further promote its large-scale production and industrial application . In order to facilitate readers to understand the paper , We have a special invitation Thermoelectric materials team of Shanghai Institute of silicate, Chinese Academy of Sciences Wrote us detailed research news . At the same time, it is aimed at the problems concerned by the field , We also invite Researcher Shi Xun The answer is : The future of academia and industry is aimed at Bi2Te3 Research interests in basic materials ? What's the next new thermoelectric system to be used ?

Thermoelectric conversion technology is a kind of new energy technology based on zebeck effect and Peltier effect of materials to realize the direct conversion of thermal energy and electric energy , It has no transmission components , Noiseless , High reliability , Long life and other advantages . In industrial waste heat recovery and utilization 、 Space special power supply 、 Microchip refrigeration and other fields have a wide range of application prospects . The energy conversion efficiency of thermoelectric technology is mainly determined by the dimensionless optimal thermoelectric value , The definition for zT=S 2 σΤ/κ, among S Is the zebeck coefficient ,σ Is electrical conductivity ,T Is the absolute temperature ,κ Is the thermal conductivity .κ From the lattice thermal conductivity κ ι And carrier thermal conductivity κ θ Two parts make up . Because of the zebeck coefficient 、 Conductivity and thermal conductivity are coupled , Therefore, it is very challenging to adjust these parameters to improve the optimal value of thermoelectricity . Using carrier concentration optimization 、 Energy filtering effect 、 Energy band engineering and other methods can effectively improve the power factor of materials S2σ; Using nanostructures , Introducing nanoscale particles or grain boundaries into thermoelectric materials , It can effectively scatter phonons with the same wavelength scale , And then the lattice thermal conductivity of the material is significantly reduced . The development of new fabrication methods and techniques to achieve controllable fabrication of nanoscale microstructures will accelerate the design and optimization of new high-performance thermoelectric materials , It is an important embodiment of nanostructured thermoelectric materials . Bi 2 Te 3 The base materials have excellent thermoelectric properties near room temperature , It is the only thermoelectric material system to realize commercial application at present . Bi 2 Te 3 It can be done with Bi 2 Te 3 Forming a continuous solid solution . because Bi Atoms and Se The atomic size and electronegativity are quite different , And Se The vapor pressure of elements is high , Bi 2 Te 3-x Se x It is easy to form a large amount of Se Vacancy leads to n Type I conduction behavior . In recent years , in the light of Bi 2 Te 3-x Se x Many achievements have been made in the study of nanostructured solid solutions , As prepared by solvothermal method Bi 2 Te 3-x Se x The nanosheets are 480 K Next zT achieve 1.23, Prepared by the solution method Bi 2 Te 2.7 Se 0.3 Nanosheets and Te Nanorod composite materials zT stay 438 K Down to 1.31. However , At present, these nanostructured methods need many steps to complete , It is difficult to realize large-scale production and industrial application . therefore , There is an urgent need to develop and Bi 2 Te 3-x Se x Nanostructure is realized by one-step synthesis , To promote its large-scale production and industrial application . picture


lately , From Dresden University of technology Bauer And so on BiTe 2 Se/Bi 2 Te 3 nucleus / One step synthesis of nanosheets with shell structure . The author passes through the NaOH/ Add... To the glycol solvent Bi(NO 3 ) 3 ∙5H 2 O,Na 2 TeO 3 ,Na 2 SeO 3 As a reactant , With a certain amount of PVP As organic ligands , stay 190℃ Next reaction , You can get it in one step Bi 2 Te 3-x Se x Nanosheets . The authors first reveal the structure of the nuclear system prepared by this method / The morphology of nanosheets with shell structure 、 structure 、 Component , And the formation mechanism is analyzed . The microstructure characterization showed that the prepared nanosheets were hexagonal , The thickness is 50 nm about , The transverse dimension is in 1-3 mm( chart 1(a)). Transmission electron microscopy (TEM) showed that all the hexagonal nanosheets had heterogeneous nuclei / Shell structure , The hexagonal nuclei are rich Se compound , The hexagonal shell is rich Te compound ( chart 2(a)). In the thickness direction, the hexagonal nanosheets have a typical layered structure ( chart 2(b)).ICP-OES and EDS The test results show that , Its precursor is Te/Se The ratio and the quality of the prepared nanosheets Te/Se Scale close , Therefore, the one-step synthesis method proposed in this study can accurately control the composition of the product ( chart 1(b),(c)). At the same time, the author uses XPS The chemical compositions of different components were studied , I found that I was using Ar It can't be observed before ion sputtering Se The peak of the mountain , But in the sputter removal surface rich Te After the shell of the compound, it can be observed that Se The peak of the mountain , It is further confirmed that the nanosheets are rich in Te shell / rich Se The core-shell structure of the core ( chart 2(c)-(e)). Further analysis shows that there is heterogeneity Core shell structure Bi 2 Te 2 Se/Bi 2 Te 3 It's formed by the inclusion of Se and Te The activity of precursor decomposition Se- and Te- Timely separation of reactants . Combined with heat treatment process (350 ℃ Anneal ) And spark plasma sintering , The effects of different treatment processes on the thermoelectric properties of the materials are systematically studied . The microstructure characterization shows that the nanocrystalline and hexagonal structure remain in the sintered products , But because of Se The spread of , After annealing and sintering, the initial core-shell nanosheets are transformed into nanosheets with continuous composition distribution . Based on the experience of annealing and sintering Bi2Te3-xSex The thermoelectric properties of the samples show that ,Bi 2 Te 2.55 Se 0.45 The component has the highest zebeck coefficient , also , Because it retains nanostructures such as grain boundaries and nanopores , It can effectively scatter phonons with the same wavelength scale , So it shows a significant decrease in thermal conductivity .Bi2Te2.55Se0.45 The thermal conductivity of the crystal lattice is only 0.15-0.25 W m -1 K -1 . Final , Of materials zT It's worth a significant improvement , stay 400K Next ,Bi2Te2.55Se0.45 In the in-plane direction zT Its value 1.34, yes n type Bi2Te3-xSex One of the highest reported values of the system , It has an important application prospect in the fields of low-grade waste heat recovery and special refrigeration . Related papers are published online in Small Science On .(DOI: 10.1002/smsc.202000021).

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chart 1 (a)Bi 2 Te 3 Bi 2 Te 3 Bi 2 Te 3-x Se x   SEM Topography ;(b) Bi 2 Te 3-x Se x In the product Te/(Te+Se) In proportion to the precursor Te/(Te+Se) The relationship of proportion ;(c) With Te:Se by 9:1 Synthesis of component nanosheets EDS Line spectrum . picture


chart 2. (a) Single Bi 2 Te 2.55 Se 0.45 In the transverse direction of the nanosheets HAADF-STEM-EELS Spectrogram ;(b) Focus on the ion beam (FIB) A thin layer cut from the thickness of the nanosheet EDS Spectrogram ;(c-e) Bi 2 Te 3 Bi 2 Te 3 Bi 2 Te 3-x Se x Before and after sputtering Se 3d Electronics XPS Analyze the structure ;(f) Three yuan Bi 2 Te 2.55 Se 0.45 Schematic diagram of the heterostructure ;(g) Raman spectroscopic analysis of binary and ternary nanosheets .

team introduction


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Shi Xun , Researcher, Shanghai Institute of silicate, Chinese Academy of Sciences , Doctoral supervisor .2000 Graduated from Tsinghua University in ,2005 He graduated from Shanghai Silicate Research Institute with a doctor's degree ,2005 year 11 In May, he was engaged in postdoctoral research in the Department of physics, University of Michigan ;2007 year 10 In June, he entered general motors R&D Research on thermoelectric materials ;2010 He was selected into the outstanding talents program of Chinese Academy of Sciences and worked in Shanghai Silicate Research Institute . stay Science、Nat. Mater.、Adv. Mater.、J. Am. Chem. Soc.、Nat. Commun.、Energy Environ. Sci. Wait for the journal to publish the paper 200 Yu Wen , quote 9000 Remaining times ; stay Nat. Mater. And so on 9 piece ; Apply for Chinese patent 16 Pieces of 、 International patent 5 Pieces of . At the international thermoelectric Congress 、 The United States MRS And other international conferences 39 Time ; He won the second prize of National Natural Science Award ( Ranking the first 3)、 International Cooperation Award for young scientists of the Chinese Academy of Sciences 、 First prize of Shanghai Natural Science Award ( Ranking the first 3)、 International thermoelectric society Young Investigator Award、 Young Scientist Award of Chinese Academy of Sciences . Undertake and preside over the national key R & D plan 、 National Science Foundation for Distinguished Young Scholars 、 Excellent Youth Science Foundation and other projects . 


SMSC: As the only commercial application Bi2Te3 Base materials , What do you think the future academic and industrial research will focus on ?

SX: Currently commercial Bi2Te3 Based thermoelectric materials are mostly prepared by zone melting method . because Bi2Te3 The chemical bonds between the layers of the compound are very weak , As a result, the mechanical properties of zone melting samples are poor , In the process of machining and device integration, materials are prone to cleavage and cracking . especially , The miniaturization and miniaturization of thermoelectric devices are very important for Bi2Te3 Higher requirements are put forward for the mechanical properties of thermoelectric materials . When Bi2Te3 The particle size in the base thermoelectric device is 0.3 Mm or less , It's very difficult to process , The yield is very low , It's severely limiting the micro Bi2Te3 Based thermoelectric devices . therefore , Through fiber reinforcement , Grain refinement and other strengthening methods Bi2Te3 The mechanical properties of the base material , Improve the processing technology of small micro devices , Improve its yield , yes Bi2Te3 One of the key directions in the future research of matrix materials . 

SMSC: In the new thermoelectric material system , What kind of materials do you think are expected to be used most quickly ? 

SX: The past two decades have been a period of rapid development of thermoelectric technology , Many new thermoelectric materials with high performance have emerged . Classified by application temperature range , These new thermoelectric materials can be roughly divided into room temperature thermoelectric materials 、 Thermoelectric materials in middle temperature zone and thermoelectric materials in high temperature zone . among ,Mg3(Sb,Bi)2 and Ag2(S,Se) The thermoelectric properties of thermoelectric materials at room temperature are close to or even better than that at some temperatures Bi2Te3 Base materials . especially , The constituent elements of these compounds are abundant in the crust , Environmentally friendly , And the machinability is better than Bi2Te3 Base materials . combination 5G Communications 、 The Internet of things and other emerging industries have an urgent demand for new high-performance room temperature thermoelectric materials , I think these Mg Kei and Ag Based thermoelectric materials are expected to be used as soon as possible . 

SMSC: What are your interests in the future of basic research on thermoelectric materials ?

SX: With more and more countries in the world advocating green environmental protection 、 Energy saving and emission reduction production and lifestyle , And the rise of some new industries , Thermoelectric energy conversion technology will be widely used in aerospace as one of the high and new technologies 、 military 、 energy 、 Environmental Science 、 Electronics 、 Communication and other fields , It has more positive effects on our quality of life and living environment . Judging from the current development trend , In my opinion, the focus of basic research on thermoelectric materials in the future should include the following three aspects : One is to develop new concepts 、 The new method cooperatively regulates the transport properties of electrons and phonons , To further improve the thermoelectric performance ; The second is to explore and discover new materials and new systems , Focus on elements with high abundance to replace precious metals ; The third is the discovery of a new phenomenon of electrothermal transport 、 New mechanism , Expand the research field and scope of thermoelectric materials .

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