Sophora leaves from several areas in Beijing are analysed by femtosecond laser-induced breakdown spectroscopy （femto-LIBS）. Although the used spectral detection system is not time-resolved, the spectral lines of tra...Sophora leaves from several areas in Beijing are analysed by femtosecond laser-induced breakdown spectroscopy （femto-LIBS）. Although the used spectral detection system is not time-resolved, the spectral lines of trace mineral elements are detected and analysed. It is proven that the femto-LIBS can be an efficient method to detect mineral trace elements contained in tree leaves which is a biomonitor for atmospheric pollution assessment or botanic studies. An interesting case of correlation between trace elements detected in tree leaves and the pollution of the concerned area is presented, for the first time to our knowledge.展开更多
An improved two-dimensional space-time conservation element and solution element （CE/SE） method with second-order accuracy is proposed, examined and extended to simulate the detonation propagations using detailed ch...An improved two-dimensional space-time conservation element and solution element （CE/SE） method with second-order accuracy is proposed, examined and extended to simulate the detonation propagations using detailed chemical reaction models. The numerical results of planar and cellular detonation are compared with corresponding results by the Chapman-Jouguet theory and experiments, and prove that the method is a new reliable way for numerical simulations of detonation propagation.展开更多
The one-to-multiparty quantum secret sharing scheme [Phys. Rev. A 71 （2005） 044301] proposed recently is extended to a multiparty-to-multiparty case. Furthermore, the continuous variable operations are employed in t...The one-to-multiparty quantum secret sharing scheme [Phys. Rev. A 71 （2005） 044301] proposed recently is extended to a multiparty-to-multiparty case. Furthermore, the continuous variable operations are employed in the extended scheme to replace the specific discrete unitary operations used in the original scheme. The complete randomicity of the continuous variable characterizing the unitary operations can ensure the security of secret sharing. Moreover, the present scheme is compared with the recent similar scheme [Phys. Rev. A 72 （2005） 012304]. It is found that the efficiency of the present scheme is n times of that of the previous one.展开更多
A method for obtaining small bottle light beams, e.g. 0.92λ×0.4λ, in a high numerical-aperture lens system is proposed and numerically demonstrated. This can be achieved by changing the radius of each zone of t...A method for obtaining small bottle light beams, e.g. 0.92λ×0.4λ, in a high numerical-aperture lens system is proposed and numerically demonstrated. This can be achieved by changing the radius of each zone of the binary element and polarization rotation angle of the cylindrically polarized vectorial vortex beam. It is found that the transversal and axial sizes of this bottle beam are equal to about 0.92λ and 0.4λ, respectively. In addition, the connection between angular momentum and topological Pancharatnam charge is also shown.展开更多
We propose a lattice Boltzmann scheme for two-dimensional complex boundaries moving in fluid flow. The hydrodynamic forces exerting on the moving boundaries are calculated based on a stress-integration method proposed...We propose a lattice Boltzmann scheme for two-dimensional complex boundaries moving in fluid flow. The hydrodynamic forces exerting on the moving boundaries are calculated based on a stress-integration method proposed before, but the extrapolation procedure is avoided, and the stability of this model is improved. The accuracy and robustness are demonstrated by numerical simulations of a circular particle settling in a twodimensional vertical channel. The numerical convergence is studied by varying the time-step and the dimensionless particle sizes.展开更多
We obtained TiNiSn-based half-Heusler Hf_(x)Ti_(1-x)NiSn_(0.97)Sb_(0.03)bulks with 85%-96%relative densities via 5-min microwave synthesis and 20-min microwave sintering in sealed vacuum.The phase composition and micr...We obtained TiNiSn-based half-Heusler Hf_(x)Ti_(1-x)NiSn_(0.97)Sb_(0.03)bulks with 85%-96%relative densities via 5-min microwave synthesis and 20-min microwave sintering in sealed vacuum.The phase composition and microstructure of samples were characterized by X-ray diffractometer(XRD)and scanning electron microscopy(SEM).Thermoelectric(TE)properties were measured,i.e.,Seebeck coefficient(S),electrical resistivity(ρ),and thermal conductivity(κ)through Seebeck coefficient/resistance analysis system(S/RAs)and laser flash thermal analyzer(LFT).The results show that the nearly single phase exists after microwave sintering.The grain sizes and the number of grain boundaries decrease with increase in Hf-doping amount due to an increase in point defects.The matrix grains for Hf_(0.1)Ti_(0.9)NiSn_(0.97)Sb_(0.03)are~10μm.The nanoscle pores and precipitates are present as second phases in matrix grain.The real composition for Hf_(0.1)Ti_(0.9)NiSn_(0.97)Sb_(0.03)matrix grain is Hf_(3.51)Ti_(28.76)-Ni_(34.76)Sn_(31.55)Sb_(1.43).The variation trends of electrical resistivity,Seebeck coefficient,power factor,and thermal conductivity were analyzed in detail.The maximum figure of merit(ZT)of 0.46 is obtained for Hf_(0.1)Ti_(0.9-)NiSnSn_(0.97)Sb_(0.03)at 723 K.The innovation route exhibits advantages for predation of TE bulks when compared to the conventional methods,especially in terms of efficiency while it still maintains TE performance.展开更多
We study the inclusive production of doubly heavy baryon Ξcc at polarized photon collider. Our results show that proper choice of the initial beam polarizations may increase the production rate of Ξcc approximately ...We study the inclusive production of doubly heavy baryon Ξcc at polarized photon collider. Our results show that proper choice of the initial beam polarizations may increase the production rate of Ξcc approximately 10%.展开更多
Pure liquid-liquid diffusion driven by concentration gradients is hard to study in a normal gravity environment since convection and sedimentation also contribute to the mass transfer process. We employ a Math Zehnder...Pure liquid-liquid diffusion driven by concentration gradients is hard to study in a normal gravity environment since convection and sedimentation also contribute to the mass transfer process. We employ a Math Zehnder interferometer to monitor the mass transfer process of a water droplet in EAFP protein solution under micro- gravity condition provided by the Satellite Shi Jian No 8, A series of the evolution charts of mass distribution during the diffusion process of the liquid droplet are presented and the relevant diffusion coefficient is determined.展开更多
We present a new substrate-free bimaterial cantilever array made of SiNx and Au for an uncooled microoptomechanical infrared imaging device. Each cantilever element has an optimized deformation magnification structure...We present a new substrate-free bimaterial cantilever array made of SiNx and Au for an uncooled microoptomechanical infrared imaging device. Each cantilever element has an optimized deformation magnification structure. A 160×160 array with a 120 μm×120μm pitch is fabricated and an optical readout is used to collectively measure deflections of all microcantilevers in the array. Thermal images of room-temperature objects with higher spatial resolution have been obtained and the noise-equivalent temperature difference of the fabricated focal plane arrays is given statistically and is measured to be about 270mK.展开更多
The electronic structures, magnetic properties, half-metallicity, and mechanical properties of half-Heulser compounds CoCrZ （Z = S, Se, and Te） were investigated using first-principles calculations within generalize...The electronic structures, magnetic properties, half-metallicity, and mechanical properties of half-Heulser compounds CoCrZ （Z = S, Se, and Te） were investigated using first-principles calculations within generalized gradient approximation based on the density function theory. The half-Heusler compounds show half-metallic properties with a half-metallic gap of 0.15 eV for CoCrS, 0.10 eV for CoCrSe, and 0.31 eV for CoCrTe at equilibrium lattice constant, respectively. The total magnetic moments are 3.00/-tB per formula unit, which agrees well with the Slater-Pauling rule. The half-metallicity, elastic constants, bulk modulus, shear modulus, Pough＇s ratio, Frantesvich ratio, Young＇s modulus, Poisson＇s ratio, and Debye temperature at equilibrium lattice constant and versus lattice constants are reported for the first time. The results indicate that the half-Heulser compounds CoCrZ （Z = S, Se, and Te） maintain the perfect half-metallic and mechanical stability within the lattice constants range of 5.18-5.43 A for CoCrS, 5.09-5.61 A for CoCrSe, and 5.17-6.42 A for CoCrTe, respectively.展开更多
The p-type TiCoSb-based half-Heuslers are widely studied due to the good electrical transport properties after hole doping,while the pristine TiCoSb is intrinsically n-type.It is thus desired to obtain a comparable n-...The p-type TiCoSb-based half-Heuslers are widely studied due to the good electrical transport properties after hole doping,while the pristine TiCoSb is intrinsically n-type.It is thus desired to obtain a comparable n-type counterpart through optimization of electron concentration.In this work,n-type Ti_(0.9-x)HfxTa_(0.1)CoSb half-Heuslers were fabricated by arc melting,ball milling,and spark plasma sintering.An optimized carrier concentration,together with a decreased lattice thermal conductivity,was obtained by Ta doping at the Ti site,leading to a peak figure of merit(ZT)of 0.7 at 973 K in Ti_(0.9)Ta_(0.1)-CoSb.By further alloying Hf at the Ti site,the lattice thermal conductivity was significantly reduced without deteriorating the power factor.As a result,a peak ZT of 0.9 at 973 K and an average ZT of 0.54 in the temperature range of 300-973 K were achieved in Ti_(0.6)Hf_(0.3)Ti_(0.1)CoSb.This work demonstrates that n-type TiCoSb-based halfHeuslers are promising thermoelectric materials.展开更多
Tailoring nanostructures is a general approach used to obtain enhanced thermoelectric properties for halfHeusler compounds because the wide areas of grain and phase boundaries could be scattering centers that lower la...Tailoring nanostructures is a general approach used to obtain enhanced thermoelectric properties for halfHeusler compounds because the wide areas of grain and phase boundaries could be scattering centers that lower lattice thermal conductivity.However,a common fabrication method based on the sintering of crystalline precursors crushed from as-cast alloy ingots has limitations in obtaining a homogeneous microstructure without microsized impurity phases,owing to residual elemental segregation from casting.In this study,we used amorphous NbCoSn alloys as a precursor for the sintered specimen to obtain a homogeneous NbCoSn bulk specimen without microsized impurity phases and segregation,which led to the enhanced Seebeck coefficient due to the high purity of the half-Heusler phase after crystallization.Moreover,superplasticity originating from amorphous features enabled the powders to be largely deformed during the sintering process,even at a low sintering temperature(953 K).This resulted in less oxidation at both,the grain boundary and the interior,as the O diffusion pathway was blocked during the sintering process.As a result,the NbCoSn0.95Sb0.05 specimen using an amorphous precursor exhibited an enhanced zT of 0.7,due to the increase in the power factor and a decrease in lattice thermal conductivity compared to the specimen using a crystalline precursor.展开更多
The thermoelectric transport properties of Zr0.43Hf0.57 NiSn half-Heusler compounds were investigated for samples sintered with different spark plasma sintering(SPS)periods:8,32 and 72 min.By means of scanning transmi...The thermoelectric transport properties of Zr0.43Hf0.57 NiSn half-Heusler compounds were investigated for samples sintered with different spark plasma sintering(SPS)periods:8,32 and 72 min.By means of scanning transmission electron microscopy with a highangular annular dark-field detector(STEM-HAADF),it was found that sintering time affected the defect concentration,namely the amount of Ni interstitial atoms,and created locally ordered inclusions of full-Heusler phase.The structural information,phase composition and electrical transport properties could be consistently explained by the assumption that Ni interstitials give rise to an impurity band situated about 100 meV below the bottom of the conduction band via a self-doping behavior.The impurity band was found to merge with the conduction band for the sample with intermediate SPS time.The effect was ascribed to the gradual dissolution of full-Heusler phase inclusions and production of interstitial Ni defects,which eventually vanished for the sample with the longest sintering time.It was demonstrated that the modification of the density of states near the edge of the conduction band and enhanced overall charge carrier concentration provided by defect engineering led to overall 26%increase in the thermoelectric figure of merit(ZT)with respect to the other samples.展开更多
ZrCoSb-based half-Heusler(HH)compounds are among the most promising thermoelectric(TE)materials for high-temperature power generation.Oxidation resistance is one of the key issues for realizing the practical applicati...ZrCoSb-based half-Heusler(HH)compounds are among the most promising thermoelectric(TE)materials for high-temperature power generation.Oxidation resistance is one of the key issues for realizing the practical application of TE materials for long-term service in the ambient working environment.In this work,the oxidation behavior of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)(ZHCSS)half-Heusler is systematically studied in the service temperature range from 873 to 1073 K.It is revealed that three typical layers of oxidation products tend to form on the surface of HH sample,namely,the dense oxide layer(DOL)composed of(Zr,Hf)O_(2) and CoSb,the alternate oxide layer(AOL)composed of repeated(Zr,Hf)O_(2) and CoSb_(2)O_(6)/Co_(3)O_(4),and the CoSb layer between the DOL and AOL.The mass gain during oxidation is mainly caused by the rapid growth of AOL,which is controlled by the outward diffusion of Zr/Hf and the inward diffusion of oxygen.The formation of a continuous CoSb layer and DOL is found beneficial to block the outward diffusion of Zr/Hf.Based on the analysis of the dominant factors on the outward and inward diffusions as well as the reaction activation energy,a simple approach is proposed to improve the oxidation resistance of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)by pre-oxidizing the sample in low oxygen pressure to form the dense(Zr,Hf)O_(2) and CoSb layers as oxidation protecting and/or diffusion blocking layers.The oxidation test shows the effectiveness of such pre-oxidation on the formation and growth of the AOL and therefore on improving the service stability of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)at high temperatures in the air.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 10634020, 10390161, 60621063, and 60478047, the National Basic Research Programme of China Grant No 2007CB815101, the National Hi-Tech ICF Project, and the Internship Scholarship from French Rahone-Alps Region.
文摘Sophora leaves from several areas in Beijing are analysed by femtosecond laser-induced breakdown spectroscopy （femto-LIBS）. Although the used spectral detection system is not time-resolved, the spectral lines of trace mineral elements are detected and analysed. It is proven that the femto-LIBS can be an efficient method to detect mineral trace elements contained in tree leaves which is a biomonitor for atmospheric pollution assessment or botanic studies. An interesting case of correlation between trace elements detected in tree leaves and the pollution of the concerned area is presented, for the first time to our knowledge.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10572002 and 10732010.
文摘An improved two-dimensional space-time conservation element and solution element （CE/SE） method with second-order accuracy is proposed, examined and extended to simulate the detonation propagations using detailed chemical reaction models. The numerical results of planar and cellular detonation are compared with corresponding results by the Chapman-Jouguet theory and experiments, and prove that the method is a new reliable way for numerical simulations of detonation propagation.
基金Supported by the programme for New Century Excellent Talents at the University of China under Grant No NCET-06-0554, the National Natural Science Foundation of China under Grant No 60677001, the Science-Technology Fund of Anhui Province for 0utstanding Youth under Grant No 06042087, the Key Fund of the Ministry of Education of China under Grant No 206063, the Postgraduate Innovation Research Plan from Anhui University under Grant No 20073039, the Natural Science Foundation of Guangdong Province under Grant Nos 06300345 and 7007806, and Natural Science Foundation of Hubei Province under Grant No 2006ABA354.
文摘The one-to-multiparty quantum secret sharing scheme [Phys. Rev. A 71 （2005） 044301] proposed recently is extended to a multiparty-to-multiparty case. Furthermore, the continuous variable operations are employed in the extended scheme to replace the specific discrete unitary operations used in the original scheme. The complete randomicity of the continuous variable characterizing the unitary operations can ensure the security of secret sharing. Moreover, the present scheme is compared with the recent similar scheme [Phys. Rev. A 72 （2005） 012304]. It is found that the efficiency of the present scheme is n times of that of the previous one.
基金Supported by the National Natural Science Foundation of China under Grant No 60477041, the Natural Science Project of the Education Bureau of Fujian Province under Grant No JA06048, and the Natural Science Project of Sanming University under Grant No B0603/G.
文摘A method for obtaining small bottle light beams, e.g. 0.92λ×0.4λ, in a high numerical-aperture lens system is proposed and numerically demonstrated. This can be achieved by changing the radius of each zone of the binary element and polarization rotation angle of the cylindrically polarized vectorial vortex beam. It is found that the transversal and axial sizes of this bottle beam are equal to about 0.92λ and 0.4λ, respectively. In addition, the connection between angular momentum and topological Pancharatnam charge is also shown.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10447001 and 10474109, the Foundation of the Ministry of Personnel of China, Shanghai Supercomputer Center of China, and the Natural Science Foundation of Guangxi Province under Grant No 0640064..The authors thank Professor H. H. Hu for provid- ing the data.
文摘We propose a lattice Boltzmann scheme for two-dimensional complex boundaries moving in fluid flow. The hydrodynamic forces exerting on the moving boundaries are calculated based on a stress-integration method proposed before, but the extrapolation procedure is avoided, and the stability of this model is improved. The accuracy and robustness are demonstrated by numerical simulations of a circular particle settling in a twodimensional vertical channel. The numerical convergence is studied by varying the time-step and the dimensionless particle sizes.
基金financially supported by the National Natural Science Foundation of China (Nos.51574134 and 51574042)the Joint Fund between Shenyang National Laboratory for Materials Science and State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals (No.18LHPY016)Anhui University Outstanding Young Talent Support Program (Key Project) (No.gxyq ZD2017039)。
文摘We obtained TiNiSn-based half-Heusler Hf_(x)Ti_(1-x)NiSn_(0.97)Sb_(0.03)bulks with 85%-96%relative densities via 5-min microwave synthesis and 20-min microwave sintering in sealed vacuum.The phase composition and microstructure of samples were characterized by X-ray diffractometer(XRD)and scanning electron microscopy(SEM).Thermoelectric(TE)properties were measured,i.e.,Seebeck coefficient(S),electrical resistivity(ρ),and thermal conductivity(κ)through Seebeck coefficient/resistance analysis system(S/RAs)and laser flash thermal analyzer(LFT).The results show that the nearly single phase exists after microwave sintering.The grain sizes and the number of grain boundaries decrease with increase in Hf-doping amount due to an increase in point defects.The matrix grains for Hf_(0.1)Ti_(0.9)NiSn_(0.97)Sb_(0.03)are~10μm.The nanoscle pores and precipitates are present as second phases in matrix grain.The real composition for Hf_(0.1)Ti_(0.9)NiSn_(0.97)Sb_(0.03)matrix grain is Hf_(3.51)Ti_(28.76)-Ni_(34.76)Sn_(31.55)Sb_(1.43).The variation trends of electrical resistivity,Seebeck coefficient,power factor,and thermal conductivity were analyzed in detail.The maximum figure of merit(ZT)of 0.46 is obtained for Hf_(0.1)Ti_(0.9-)NiSnSn_(0.97)Sb_(0.03)at 723 K.The innovation route exhibits advantages for predation of TE bulks when compared to the conventional methods,especially in terms of efficiency while it still maintains TE performance.
基金Supported by the National Natural Science Foundation of China, the New Century Excellent Talent Project （NCET） of the Ministry of Education of China, and HuoYingDong Foundation of China.
文摘We study the inclusive production of doubly heavy baryon Ξcc at polarized photon collider. Our results show that proper choice of the initial beam polarizations may increase the production rate of Ξcc approximately 10%.
文摘Pure liquid-liquid diffusion driven by concentration gradients is hard to study in a normal gravity environment since convection and sedimentation also contribute to the mass transfer process. We employ a Math Zehnder interferometer to monitor the mass transfer process of a water droplet in EAFP protein solution under micro- gravity condition provided by the Satellite Shi Jian No 8, A series of the evolution charts of mass distribution during the diffusion process of the liquid droplet are presented and the relevant diffusion coefficient is determined.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10472111, 10732080 and 10627201, and the National Basic Research Programme of China under Grant No 2006CB300404.
文摘We present a new substrate-free bimaterial cantilever array made of SiNx and Au for an uncooled microoptomechanical infrared imaging device. Each cantilever element has an optimized deformation magnification structure. A 160×160 array with a 120 μm×120μm pitch is fabricated and an optical readout is used to collectively measure deflections of all microcantilevers in the array. Thermal images of room-temperature objects with higher spatial resolution have been obtained and the noise-equivalent temperature difference of the fabricated focal plane arrays is given statistically and is measured to be about 270mK.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11647133 and 11674113)the Natural Science Foundation of Hubei Province,China(Grant Nos.2017CFB740 and 2014CFB631)+1 种基金the Scientific Research Items Foundation of Hubei Educational Committee,China(Grant Nos.Q20141802,Q20161803,B2016091,and D20171803)Hubei Provincial Collaborative Innovation Center for Optoelectronics,China
文摘The electronic structures, magnetic properties, half-metallicity, and mechanical properties of half-Heulser compounds CoCrZ （Z = S, Se, and Te） were investigated using first-principles calculations within generalized gradient approximation based on the density function theory. The half-Heusler compounds show half-metallic properties with a half-metallic gap of 0.15 eV for CoCrS, 0.10 eV for CoCrSe, and 0.31 eV for CoCrTe at equilibrium lattice constant, respectively. The total magnetic moments are 3.00/-tB per formula unit, which agrees well with the Slater-Pauling rule. The half-metallicity, elastic constants, bulk modulus, shear modulus, Pough＇s ratio, Frantesvich ratio, Young＇s modulus, Poisson＇s ratio, and Debye temperature at equilibrium lattice constant and versus lattice constants are reported for the first time. The results indicate that the half-Heulser compounds CoCrZ （Z = S, Se, and Te） maintain the perfect half-metallic and mechanical stability within the lattice constants range of 5.18-5.43 A for CoCrS, 5.09-5.61 A for CoCrSe, and 5.17-6.42 A for CoCrTe, respectively.
基金financially supported by the National Natural Science Foundation of China(Nos.51971081 and 11674078)the Natural Science Foundation for Distinguished Young Scholars of Guangdong Province of China(No.202031515020023)Shenzhen Science and Technology Innovation Plan(No.KQJSCX20180328165435202)。
文摘The p-type TiCoSb-based half-Heuslers are widely studied due to the good electrical transport properties after hole doping,while the pristine TiCoSb is intrinsically n-type.It is thus desired to obtain a comparable n-type counterpart through optimization of electron concentration.In this work,n-type Ti_(0.9-x)HfxTa_(0.1)CoSb half-Heuslers were fabricated by arc melting,ball milling,and spark plasma sintering.An optimized carrier concentration,together with a decreased lattice thermal conductivity,was obtained by Ta doping at the Ti site,leading to a peak figure of merit(ZT)of 0.7 at 973 K in Ti_(0.9)Ta_(0.1)-CoSb.By further alloying Hf at the Ti site,the lattice thermal conductivity was significantly reduced without deteriorating the power factor.As a result,a peak ZT of 0.9 at 973 K and an average ZT of 0.54 in the temperature range of 300-973 K were achieved in Ti_(0.6)Hf_(0.3)Ti_(0.1)CoSb.This work demonstrates that n-type TiCoSb-based halfHeuslers are promising thermoelectric materials.
基金the Basic Science Research Program of the National Research Foundation of Korea(NRF)(Nos.2021R1A4A2001658 and 2021R1A6A3A03045488).
文摘Tailoring nanostructures is a general approach used to obtain enhanced thermoelectric properties for halfHeusler compounds because the wide areas of grain and phase boundaries could be scattering centers that lower lattice thermal conductivity.However,a common fabrication method based on the sintering of crystalline precursors crushed from as-cast alloy ingots has limitations in obtaining a homogeneous microstructure without microsized impurity phases,owing to residual elemental segregation from casting.In this study,we used amorphous NbCoSn alloys as a precursor for the sintered specimen to obtain a homogeneous NbCoSn bulk specimen without microsized impurity phases and segregation,which led to the enhanced Seebeck coefficient due to the high purity of the half-Heusler phase after crystallization.Moreover,superplasticity originating from amorphous features enabled the powders to be largely deformed during the sintering process,even at a low sintering temperature(953 K).This resulted in less oxidation at both,the grain boundary and the interior,as the O diffusion pathway was blocked during the sintering process.As a result,the NbCoSn0.95Sb0.05 specimen using an amorphous precursor exhibited an enhanced zT of 0.7,due to the increase in the power factor and a decrease in lattice thermal conductivity compared to the specimen using a crystalline precursor.
基金financially supported by German Research Foundation Priority Programme 1386(No.WE 2803/2-2)the European Union under Marie Sklodowska-Curie Program(W.J.X.)。
文摘The thermoelectric transport properties of Zr0.43Hf0.57 NiSn half-Heusler compounds were investigated for samples sintered with different spark plasma sintering(SPS)periods:8,32 and 72 min.By means of scanning transmission electron microscopy with a highangular annular dark-field detector(STEM-HAADF),it was found that sintering time affected the defect concentration,namely the amount of Ni interstitial atoms,and created locally ordered inclusions of full-Heusler phase.The structural information,phase composition and electrical transport properties could be consistently explained by the assumption that Ni interstitials give rise to an impurity band situated about 100 meV below the bottom of the conduction band via a self-doping behavior.The impurity band was found to merge with the conduction band for the sample with intermediate SPS time.The effect was ascribed to the gradual dissolution of full-Heusler phase inclusions and production of interstitial Ni defects,which eventually vanished for the sample with the longest sintering time.It was demonstrated that the modification of the density of states near the edge of the conduction band and enhanced overall charge carrier concentration provided by defect engineering led to overall 26%increase in the thermoelectric figure of merit(ZT)with respect to the other samples.
基金financially supported by the National Key Research and Development Program of China(Grant No.2019YFE0103500)the National Nature Science Foundation of China(NSFC)(Grant Nos.U2141208 and 52102330)+1 种基金and the In-ternational Partnership Program of Chinese Academy of Sciences(Grant No.121631KYSB20200012)the support from CAS Key Technology Talent Program.
文摘ZrCoSb-based half-Heusler(HH)compounds are among the most promising thermoelectric(TE)materials for high-temperature power generation.Oxidation resistance is one of the key issues for realizing the practical application of TE materials for long-term service in the ambient working environment.In this work,the oxidation behavior of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)(ZHCSS)half-Heusler is systematically studied in the service temperature range from 873 to 1073 K.It is revealed that three typical layers of oxidation products tend to form on the surface of HH sample,namely,the dense oxide layer(DOL)composed of(Zr,Hf)O_(2) and CoSb,the alternate oxide layer(AOL)composed of repeated(Zr,Hf)O_(2) and CoSb_(2)O_(6)/Co_(3)O_(4),and the CoSb layer between the DOL and AOL.The mass gain during oxidation is mainly caused by the rapid growth of AOL,which is controlled by the outward diffusion of Zr/Hf and the inward diffusion of oxygen.The formation of a continuous CoSb layer and DOL is found beneficial to block the outward diffusion of Zr/Hf.Based on the analysis of the dominant factors on the outward and inward diffusions as well as the reaction activation energy,a simple approach is proposed to improve the oxidation resistance of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)by pre-oxidizing the sample in low oxygen pressure to form the dense(Zr,Hf)O_(2) and CoSb layers as oxidation protecting and/or diffusion blocking layers.The oxidation test shows the effectiveness of such pre-oxidation on the formation and growth of the AOL and therefore on improving the service stability of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)at high temperatures in the air.
