The effects of magnetization on the phase composition,microstructure and thermoelectric transport properties of CoSb_(3)were studied systematically.The magnetic properties of CoSb_(3)material were also measured at roo...The effects of magnetization on the phase composition,microstructure and thermoelectric transport properties of CoSb_(3)were studied systematically.The magnetic properties of CoSb_(3)material were also measured at room temperature in order to confirm its magnetic category.The results of XRD and FESEM analysis indicated that the phase composition and microstructure of the CoSb_(3)were not affected by magnetization.The results of thermoelectric transport measurement showed that the electrical and thermal transport properties of materials were also not affected by magnetization.These results were mainly attributed to the diamagnetism of the CoSb_(3)material,which were consistent with the results of the magnetic properties measurement.This study is expected to provide a special research perspective for studying the effects of the external conditions on the structure and properties of thermoelectric materials.展开更多
The great pressure of energy shortage has made CoSb_(3) materials with excellent mechanical stability in the mid-temperature region favored for the integration of thermoelectric devices.However,their ex-cessive lattic...The great pressure of energy shortage has made CoSb_(3) materials with excellent mechanical stability in the mid-temperature region favored for the integration of thermoelectric devices.However,their ex-cessive lattice thermal conductivity and poor Seebeck coefficient lead to low energy conversion effi-ciency.Filling Yb into the lattice void to optimize the band structure and regulate the chemical po-tential is an indispensable means for improving the thermoelectric properties of CoSb_(3)-based materials,while the phase structure and thermoelectric properties vary with the preparation process.This motivates the current work to focus on the influence of annealing temperature on the microstructure and thermoelectric properties of Yb-filled CoSb_(3).Experimental analysis and theoretical model eluci-dated that an increase in annealing temperature can optimize the Yb filling fraction,which simulta-neously manipulates the band structure as well as chemical potential,resulting in an excellent electrical property.Furthermore,the phase and microstructure characterization clarify that the annealing temperature can effectively affect the grain size.The complex grain boundary induced by grain refinement,more filled Yb atoms and precipitates strongly scatter wide-frequency phonons,significantly suppressing the lattice thermal conductivity.As a result,a superior dimensionless figure of merit(ZT)value of~1.33 at 823 K and an average ZTave of~0.9(323-823 K)were achieved in the Ybo.4Co4Sb12 sample annealed at 923 K,and the calculated conversion efficiency could reach~13%.This work pro-vides a unique paradigm to improve thermoelectrics in the filled CoSb_(3)-based skutterudites by annealing engineering.展开更多
Molecular dynamics simulations are implemented to study the mechanical fracture of CoSb_(3) with penetrated nanocracks under the mode-Ⅰ stress.The crack surface and crack front direction are(100)and[001],respectively...Molecular dynamics simulations are implemented to study the mechanical fracture of CoSb_(3) with penetrated nanocracks under the mode-Ⅰ stress.The crack surface and crack front direction are(100)and[001],respectively.It is found that,at a fixed initial crack length,the fracture strength varies with the sample size,but the calculated value of fracture toughness KIC,by employing the classical formula of linear elastic fracture mechanics,maintains constant.When the crack is short in length relative to the sample,the variation of the fracture strength with the initial crack length is well fitted mathematically,and the extrapolation shows rationality even up to the macroscale.More general analyses reveal that,the fracture toughness increases monotonically with increasing the initial crack length until reaching the limit,and the increment is particularly noticeable below 36 nm.Furthermore,different atomic configurations at the crack tip are considered,which show an evident influence on the strength of nano-cracked CoSb_(3).展开更多
The binary skutterudite CoSb_(3) is a narrow bandgap semiconductor thermoelectric(TE)material with a relatively flat band structure and excellent electrical performance.However,thermal conductivity is very high becaus...The binary skutterudite CoSb_(3) is a narrow bandgap semiconductor thermoelectric(TE)material with a relatively flat band structure and excellent electrical performance.However,thermal conductivity is very high because of the covalent bond between Co and Sb,resulting in a very low ZT value.Therefore,researchers have been trying to reduce its thermal conductivity by the different optimization methods.In addition,the synergistic optimization of the electrical and thermal transport parameters is also a key to improve the ZT value of CoSb_(3) material because the electrical and thermal transport parameters of TE materials are closely related to each other by the band structure and scattering mechanism.This review summarizes the main research progress in recent years to reduce the thermal conductivity of CoSb_(3)-based materials at atomic-molecular scale and nano-mesoscopic scale.We also provide a simple summary of achievements made in recent studies on the non-equilibrium preparation technologies of CoSb_(3)-based materials and synergistic optimization of the electrical and thermal transport parameters.In addition,the research progress of CoSb_(3)-based TE devices in recent years is also briefly discussed.展开更多
Owing to the unique features,such as mechanically robust,low-toxic,high stability,and high thermoelectric performance,CoSb_(3)-based skutterudite materials are among art-of-the state thermoelectric candidates.In this ...Owing to the unique features,such as mechanically robust,low-toxic,high stability,and high thermoelectric performance,CoSb_(3)-based skutterudite materials are among art-of-the state thermoelectric candidates.In this work,we develop a facile in-situ method for the growth of well-crystallinity(Ag,Sn)co-doped CoSb_(3)thin films.This preparation method can efficiently control the dopant concentration and distribution in the thin films.Both the density functional theory calculation and the experimental results suggest that Sn and Ag dopants trend to enter the lattice and preferentially fill interstitial sites.Additionally,band structure calculation results suggest that the Fermi level moves into the conduction bands due to co-doping and eventually induces the increased electrical conductivity,which agrees with the optimization of carrier concentration.Moreover,an increase in the density of state after co-doping is responsible for the increased Seebeck coefficient.As a result,the power factors of(Ag,Sn)co-doped CoSb_(3)thin films are greatly enhanced,and the maximum power factor achieves over 0.3 m W m^(-1)K^(-2)at 623 K,which is almost two times than that of the un-doped CoSb_(3)film.Multiple microstructures,including Sb vacancies and Ag/Sn interstitial atoms as point defects,and a high density of lattice distortions coupled with nano-sized Ag-rich grains,lead to all scale phonon scatterings.As a result,a reduced thermal conductivity of~0.28 W m^(-1)K^(-1)and a maximum ZT of~0.52 at 623 K are obtained from(Ag,Sn)co-doped CoSb_(3)thin films.This study indicates our facile in-situ growth can be used to develop high-performance dual doped CoSb_(3)thins.展开更多
The binary CoSb_(3) skutterudite thermoelectric material has high thermal conductivity due to the covalent bond between Co and Sb, and the thermoelectric figure of merit, ZT, is very low. The thermal conductivity of C...The binary CoSb_(3) skutterudite thermoelectric material has high thermal conductivity due to the covalent bond between Co and Sb, and the thermoelectric figure of merit, ZT, is very low. The thermal conductivity of CoSb_(3) materials can be significantly reduced through phonon engineering, such as low-dimensional structure, the introduction of nano second phases,nanointerfaces or nanopores, which greatly improves their ZT values. The phonon engineering can optimize significantly the thermal transport properties of CoSb_(3)-based materials. However, the improvement of the electronic transport properties is not obvious, or even worse. Energy band and charge-carrier engineering can significantly improve the electronic transport properties of CoSb_(3)-based materials while optimizing the thermal transport properties. Therefore, the decoupling of thermal and electronic transport properties of CoSb_(3)-based materials can be realized by energy band and charge-carrier engineering. This review summarizes some methods of optimizing synergistically the electronic and thermal transport properties of CoSb_(3) materials through the energy band and charge-carrier engineering strategies. Energy band engineering strategies include band convergence or resonant energy levels caused by doping/filling. The charge-carrier engineering strategy includes the optimization of carrier concentration and mobility caused by doping/filling, forming modulation doped structures or introducing nano second phase. These strategies are effective means to improve performance of thermoelectric materials and provide new research ideas of development of high-efficiency thermoelectric materials.展开更多
Upon uniaxial compressive loading at 500℃(T/Tm=0.67,where Tm is the absolute melting point),the n-type Skutterudite alloy Yb03Co4Sb12 deforms plastically by creep via a power-law,with a stress exponent~3 consistent w...Upon uniaxial compressive loading at 500℃(T/Tm=0.67,where Tm is the absolute melting point),the n-type Skutterudite alloy Yb03Co4Sb12 deforms plastically by creep via a power-law,with a stress exponent~3 consistent with dislocation viscous glide.An activation energy of 171 kJ/mol is measured over the temperature range of 500-587℃(T/Tm=0.67-0.75)at a stress of 30 MPa.Yb_(0.3)Co_(4)Sb_(12)is ductile at 500℃,exhibiting a compressive strain of 25%when subjected to stresses ranging from 22 to 90 MPa for up to 28 days.Among the thermoelectric materials tested so far for creep,Yb_(0.3)Co_(4)Sb_(12)exhibits a creep resistance intermediate between low-melting(Bi2Te3,TAGS-85)and high-melting thermoelectrics(Mg2Si and ZrNiSn).A relatively modest drop in the figure of merit zT,from 0.67 to 0.52,is displayed by Yb_(0.3)Co_(4)Sb_(12)after accumulating 3.7%compressive creep strain at 500℃,mostly due to a drop in electrical conductivity.展开更多
基金Funded by National Natural Science Foundation of China(No.51872006)High Level Doctoral Talent Program of Anhui University of Technology(No.DT17200008)。
文摘The effects of magnetization on the phase composition,microstructure and thermoelectric transport properties of CoSb_(3)were studied systematically.The magnetic properties of CoSb_(3)material were also measured at room temperature in order to confirm its magnetic category.The results of XRD and FESEM analysis indicated that the phase composition and microstructure of the CoSb_(3)were not affected by magnetization.The results of thermoelectric transport measurement showed that the electrical and thermal transport properties of materials were also not affected by magnetization.These results were mainly attributed to the diamagnetism of the CoSb_(3)material,which were consistent with the results of the magnetic properties measurement.This study is expected to provide a special research perspective for studying the effects of the external conditions on the structure and properties of thermoelectric materials.
基金supported by the National Key Research and Development Program of China (Grant Nos.2018YFA0702100 and 2022YFB3803900)the Joint Funds of the National Natural Science Foundation of China and the Chinese Academy of Sciences (CAS)’Large-Scale Scientific Facility (Grant No.U1932106)the Sichuan University Innovation Research Pro-gram of China (Grant No.2020SCUNL112).
文摘The great pressure of energy shortage has made CoSb_(3) materials with excellent mechanical stability in the mid-temperature region favored for the integration of thermoelectric devices.However,their ex-cessive lattice thermal conductivity and poor Seebeck coefficient lead to low energy conversion effi-ciency.Filling Yb into the lattice void to optimize the band structure and regulate the chemical po-tential is an indispensable means for improving the thermoelectric properties of CoSb_(3)-based materials,while the phase structure and thermoelectric properties vary with the preparation process.This motivates the current work to focus on the influence of annealing temperature on the microstructure and thermoelectric properties of Yb-filled CoSb_(3).Experimental analysis and theoretical model eluci-dated that an increase in annealing temperature can optimize the Yb filling fraction,which simulta-neously manipulates the band structure as well as chemical potential,resulting in an excellent electrical property.Furthermore,the phase and microstructure characterization clarify that the annealing temperature can effectively affect the grain size.The complex grain boundary induced by grain refinement,more filled Yb atoms and precipitates strongly scatter wide-frequency phonons,significantly suppressing the lattice thermal conductivity.As a result,a superior dimensionless figure of merit(ZT)value of~1.33 at 823 K and an average ZTave of~0.9(323-823 K)were achieved in the Ybo.4Co4Sb12 sample annealed at 923 K,and the calculated conversion efficiency could reach~13%.This work pro-vides a unique paradigm to improve thermoelectrics in the filled CoSb_(3)-based skutterudites by annealing engineering.
基金funding was provided by the National Natural Science Foundation of China(No.51972253).
文摘Molecular dynamics simulations are implemented to study the mechanical fracture of CoSb_(3) with penetrated nanocracks under the mode-Ⅰ stress.The crack surface and crack front direction are(100)and[001],respectively.It is found that,at a fixed initial crack length,the fracture strength varies with the sample size,but the calculated value of fracture toughness KIC,by employing the classical formula of linear elastic fracture mechanics,maintains constant.When the crack is short in length relative to the sample,the variation of the fracture strength with the initial crack length is well fitted mathematically,and the extrapolation shows rationality even up to the macroscale.More general analyses reveal that,the fracture toughness increases monotonically with increasing the initial crack length until reaching the limit,and the increment is particularly noticeable below 36 nm.Furthermore,different atomic configurations at the crack tip are considered,which show an evident influence on the strength of nano-cracked CoSb_(3).
基金supported by the National Natural Science Foundation of China(Grant No.51872006)High Level Doctoral Talent Program of Anhui University of Technology(DT17200008)National Undergraduate Training Programs for Innovation and Entrepreneurship(No.S201910360186).
文摘The binary skutterudite CoSb_(3) is a narrow bandgap semiconductor thermoelectric(TE)material with a relatively flat band structure and excellent electrical performance.However,thermal conductivity is very high because of the covalent bond between Co and Sb,resulting in a very low ZT value.Therefore,researchers have been trying to reduce its thermal conductivity by the different optimization methods.In addition,the synergistic optimization of the electrical and thermal transport parameters is also a key to improve the ZT value of CoSb_(3) material because the electrical and thermal transport parameters of TE materials are closely related to each other by the band structure and scattering mechanism.This review summarizes the main research progress in recent years to reduce the thermal conductivity of CoSb_(3)-based materials at atomic-molecular scale and nano-mesoscopic scale.We also provide a simple summary of achievements made in recent studies on the non-equilibrium preparation technologies of CoSb_(3)-based materials and synergistic optimization of the electrical and thermal transport parameters.In addition,the research progress of CoSb_(3)-based TE devices in recent years is also briefly discussed.
基金supported by Guangdong Basic and Applied Basic Research Foundation(2020A1515010515 and 2019A1515110107)National Natural Science Foundation of China(11604212)Australian Research Council。
文摘Owing to the unique features,such as mechanically robust,low-toxic,high stability,and high thermoelectric performance,CoSb_(3)-based skutterudite materials are among art-of-the state thermoelectric candidates.In this work,we develop a facile in-situ method for the growth of well-crystallinity(Ag,Sn)co-doped CoSb_(3)thin films.This preparation method can efficiently control the dopant concentration and distribution in the thin films.Both the density functional theory calculation and the experimental results suggest that Sn and Ag dopants trend to enter the lattice and preferentially fill interstitial sites.Additionally,band structure calculation results suggest that the Fermi level moves into the conduction bands due to co-doping and eventually induces the increased electrical conductivity,which agrees with the optimization of carrier concentration.Moreover,an increase in the density of state after co-doping is responsible for the increased Seebeck coefficient.As a result,the power factors of(Ag,Sn)co-doped CoSb_(3)thin films are greatly enhanced,and the maximum power factor achieves over 0.3 m W m^(-1)K^(-2)at 623 K,which is almost two times than that of the un-doped CoSb_(3)film.Multiple microstructures,including Sb vacancies and Ag/Sn interstitial atoms as point defects,and a high density of lattice distortions coupled with nano-sized Ag-rich grains,lead to all scale phonon scatterings.As a result,a reduced thermal conductivity of~0.28 W m^(-1)K^(-1)and a maximum ZT of~0.52 at 623 K are obtained from(Ag,Sn)co-doped CoSb_(3)thin films.This study indicates our facile in-situ growth can be used to develop high-performance dual doped CoSb_(3)thins.
基金supported by the National Natural Science Foundation of China (Grant No. 51872006)the Excellent Youth Project of Natural Science Foundation of Anhui Province of China (Grant No. 2208085Y17)。
文摘The binary CoSb_(3) skutterudite thermoelectric material has high thermal conductivity due to the covalent bond between Co and Sb, and the thermoelectric figure of merit, ZT, is very low. The thermal conductivity of CoSb_(3) materials can be significantly reduced through phonon engineering, such as low-dimensional structure, the introduction of nano second phases,nanointerfaces or nanopores, which greatly improves their ZT values. The phonon engineering can optimize significantly the thermal transport properties of CoSb_(3)-based materials. However, the improvement of the electronic transport properties is not obvious, or even worse. Energy band and charge-carrier engineering can significantly improve the electronic transport properties of CoSb_(3)-based materials while optimizing the thermal transport properties. Therefore, the decoupling of thermal and electronic transport properties of CoSb_(3)-based materials can be realized by energy band and charge-carrier engineering. This review summarizes some methods of optimizing synergistically the electronic and thermal transport properties of CoSb_(3) materials through the energy band and charge-carrier engineering strategies. Energy band engineering strategies include band convergence or resonant energy levels caused by doping/filling. The charge-carrier engineering strategy includes the optimization of carrier concentration and mobility caused by doping/filling, forming modulation doped structures or introducing nano second phase. These strategies are effective means to improve performance of thermoelectric materials and provide new research ideas of development of high-efficiency thermoelectric materials.
基金supported by the NASA Science Missions Directorate’s Radioisotope Power Systems Technology Advancement Program.This work made use of the MatCI Facility which receives support from the MRSEC Program(NSF DMR-1720139)of the Materials Research Center at Northwestern University.This work made use,as well,of the EPIC facility of Northwestern University’s NUANCE Center,which has received support from the Soft and Hybrid Nanotechnology Experimental(SHyNE)Resource(NSF ECCS-1542205)the MRSEC program(NSF DMR-1720139)at the Materials Research Center+3 种基金the International Institute for Nanotechnology(IIN)the Keck Foundationthe State of Illinois,through the IIN.This work also made use of the IMSERC at Northwestern University,which has received support from the Soft and Hybrid Nanotechnology Experimental(SHyNE)Resource(NSF ECCS-1542205)the State of Illinois and International Institute for Nanotechnology(IIN).GJS Acknowledges support from the NASA Science Mission Directorate’s Radioisotope Power Systems Thermoelectric Technology Development program.
文摘Upon uniaxial compressive loading at 500℃(T/Tm=0.67,where Tm is the absolute melting point),the n-type Skutterudite alloy Yb03Co4Sb12 deforms plastically by creep via a power-law,with a stress exponent~3 consistent with dislocation viscous glide.An activation energy of 171 kJ/mol is measured over the temperature range of 500-587℃(T/Tm=0.67-0.75)at a stress of 30 MPa.Yb_(0.3)Co_(4)Sb_(12)is ductile at 500℃,exhibiting a compressive strain of 25%when subjected to stresses ranging from 22 to 90 MPa for up to 28 days.Among the thermoelectric materials tested so far for creep,Yb_(0.3)Co_(4)Sb_(12)exhibits a creep resistance intermediate between low-melting(Bi2Te3,TAGS-85)and high-melting thermoelectrics(Mg2Si and ZrNiSn).A relatively modest drop in the figure of merit zT,from 0.67 to 0.52,is displayed by Yb_(0.3)Co_(4)Sb_(12)after accumulating 3.7%compressive creep strain at 500℃,mostly due to a drop in electrical conductivity.
