We theoretically present the intrinsic limits to electron mobility in the modulation-doped AIGaN/GaN two-dimensional electron gas (2DEG) due to effects including acoustic deformation potential (DP) scattering, pie...We theoretically present the intrinsic limits to electron mobility in the modulation-doped AIGaN/GaN two-dimensional electron gas (2DEG) due to effects including acoustic deformation potential (DP) scattering, piezoelectric scattering (PE), and polar-optic phonon scattering (POP). We find that DE and PE are the more significant limiting factors at intermediate temperatures of 40 K to 250 K, while POP becomes dominant as room temperature is approached. Detailed numerical results are presented for the change of electron mobility with respect to temperature and carrier density. We conclude that these three types of phonon scattering, which are generally determined by the material properties but not the technical processing, are hard limits to the 2DEG mobility.展开更多
Known as a weak topological insulator(TI),BiSe structurally exhibits alternating stacks of quantum spin Hall bilayer("Bi_(2)")and three-dimensional TI layer("Bi_(2)Se_(3)").The low lattice thermal ...Known as a weak topological insulator(TI),BiSe structurally exhibits alternating stacks of quantum spin Hall bilayer("Bi_(2)")and three-dimensional TI layer("Bi_(2)Se_(3)").The low lattice thermal conductivity of BiSe due to the presence of Bi2 bilayers promises potentially good thermoelectric performance.Herein,the thermoelectric properties of nominal Bi_(1-x)Cu_(x)Se samples were studied as the functions of the content of Cu additive and temperature.It is found that Cu additives in BiSe(1)profoundly affect the texture of densified polycrystalline samples by inclining the crystallographic c-axis parallel toward the pressure direction in the densification process,(2)increase considerably the effective mass and thus the Seebeck coefficient,and(3)yield point defects and Cu-Se secondary phases that effectively scatter heat-carrying phonons.As a result,the optimized electrical and thermal properties yield a thermoelectric figure of merit of zT~0.29 in Bi_(1-x)Cu_(x)Se(x=0.03)sample at 467 K in parallel to the pressure direction and a zT~0.20 at 468 K in the perpendicular direction.展开更多
Two dimensional excitonic devices are of great potential to overcome the dilemma of response time and integration in current generation of electron or/and photon based systems.The ultrashort diffusion length of excito...Two dimensional excitonic devices are of great potential to overcome the dilemma of response time and integration in current generation of electron or/and photon based systems.The ultrashort diffusion length of exciton arising from ultrafast relaxation and low carrier mobility greatly discounts the performance of excitonic devices.Phonon scattering and exciton localization are crucial to understand the modulation of exciton flux in two dimensional disorder energy landscape,which still remain elusive.Here,we report an optimized scheme for exciton diffusion and relaxation dominated by phonon scattering and disorder potentials in WSe2 monolayers.The effective diffusion coefficient is enhanced by>200%at 280 K.The excitons tend to be localized by disorder potentials accompanied by the steadily weakening of phonon scattering when temperature drops to 260 K,and the onset of exciton localization brings forward as decreasing temperature.These findings identify that phonon scattering and disorder potentials are of great importance for long-range exciton diffusion and thermal management in exciton based systems,and lay a firm foundation for the development of functional excitonic devices.展开更多
The heat conduction and thermal conductivity for methane hydrate are simulated from equilibrium molecular dynamics. The thermal conductivity and temperature dependence trend agree well with the experimental results. T...The heat conduction and thermal conductivity for methane hydrate are simulated from equilibrium molecular dynamics. The thermal conductivity and temperature dependence trend agree well with the experimental results. The nonmonotonic temperature dependence is attributed to the phonon inelastic scattering at higher temperature and to the confinement of the optic phonon modes and low frequency phonons at low temperature. The thermal conductivity scales proportionally with the van der Waals interaction strength, The conversion of a crystal-like nature into an amorphous one oecurs at higher strength. Both the temperature dependence and interaction strength dependence are explained by phonon inelastic scattering.展开更多
This paper introduces a new method for a formula for electron spin relaxation time of a system of electrons interacting with phonons through phonon-modulated spin-orbit coupling using the projection-reduction method. ...This paper introduces a new method for a formula for electron spin relaxation time of a system of electrons interacting with phonons through phonon-modulated spin-orbit coupling using the projection-reduction method. The phonon absorption and emission processes as well as the photon absorption and emission processes in all electron transition processes can be explained in an organized manner, and the result can be represented in a diagram that can provide intuition for the quantum dynamics of electrons in a solid. The temperature (T) dependence of electron spin relaxation times (T1) in silicon is T1 ∝ T-1.07 at low temperatures and T1 ∝ T-3.3 at high temperatures for acoustic deformation constant Pad = 1.4 × 10^7 eV and optical deformation constant Pod = 4.0 × 10^17 eV/m. This means that electrons are scattered by the acoustic deformation phonons at low temperatures and optical deformation phonons at high temperatures, respectively. The magnetic field (B) dependence of the relaxation times is T1 ∝ B-2.7 at 100 K and T1 ∝ B-2.3 at 150 K, which nearly agree with the result of Yafet, T1 ∝ B-3.0- B -2.5.展开更多
Multiferroic materials are promising candidates for next-generation multi-functional devices, because of the coexistence of multi-orders and the coupling between the orders. FeVO4 has been confirmed to be a multiferro...Multiferroic materials are promising candidates for next-generation multi-functional devices, because of the coexistence of multi-orders and the coupling between the orders. FeVO4 has been confirmed to be a multiferroic compound,since it exhibits both ferroelectricity and antiferromagnetic ordering at low temperatures. In this paper, we have performed careful Raman scattering measurements on high-quality Fe VO4 single crystals. The compound has a very rich phonon structure due to its low crystal symmetry(P- 1) and at least 47 Raman-active phonon modes have been resolved in the low and hightemperature spectra. Most of the observed modes are well assigned with aid of first-principles calculations and symmetry analysis. The present study provides an experimental basis for exploring spin-lattice coupling and the mechanism of multiferroicity in FeVO4展开更多
Trap-assisted tunneling(TAT) has attracted more and more attention, because it seriously affects the sub-threshold characteristic of tunnel field-effect transistor(TFET). In this paper, we assess subthreshold perf...Trap-assisted tunneling(TAT) has attracted more and more attention, because it seriously affects the sub-threshold characteristic of tunnel field-effect transistor(TFET). In this paper, we assess subthreshold performance of double gate TFET(DG-TFET) through a band-to-band tunneling(BTBT) model, including phonon-assisted scattering and acoustic surface phonons scattering. Interface state density profile(D_(it)) and the trap level are included in the simulation to analyze their effects on TAT current and the mechanism of gate leakage current.展开更多
Thermoelectric materials,enabling the directing conversion between heat and electricity,are one of the promising candidates for overcoming environmental pollution and the upcoming energy shortage caused by the over-co...Thermoelectric materials,enabling the directing conversion between heat and electricity,are one of the promising candidates for overcoming environmental pollution and the upcoming energy shortage caused by the over-consumption of fossil fuels.Bi2Te3-based alloys are the classical thermoelectric materials working near room temperature.Due to the intensive theoretical investigations and experimental demonstrations,significant progress has been achieved to enhance the thermoelectric performance of Bi2Te3-based thermoelectric materials.In this review,we first explored the fundamentals of thermoelectric effect and derived the equations for thermoelectric properties.On this basis,we studied the effect of material parameters on thermoelectric properties.Then,we analyzed the features of Bi2Te3-based thermoelectric materials,including the lattice defects,anisotropic behavior and the strong bipolar conduction at relatively high temperature.Then we accordingly summarized the strategies for enhancing the thermoelectric performance,including point defect engineering,texture alignment,and band gap enlargement.Moreover,we highlighted the progress in decreasing thermal conductivity using nanostructures fabricated by solution grown method,ball milling,and melt spinning.Lastly,we employed modeling analysis to uncover the principles of anisotropy behavior and the achieved enhancement in Bi2Te3,which will enlighten the enhancement of thermoelectric performance in broader materials展开更多
The thermoelectric materials have been considered as a potential candidate for the new power generation technology based on their reversible heat and electricity conversion.Lead telluride(Pb Te) is regarded as an ex...The thermoelectric materials have been considered as a potential candidate for the new power generation technology based on their reversible heat and electricity conversion.Lead telluride(Pb Te) is regarded as an excellent mid-temperature thermoelectric material due to its suitable intrinsic thermoelectric properties.So tremendous efforts have been done to improve the thermoelectric performance of Pb Te,and figures of merit,zT 〉 2.0,have been reported.Main strategies for optimizing the thermoelectric performance have been focused as the main line of this review.The band engineering and phonon scattering engineering as two main effective strategies are systemically summarized here.The band engineering,like band convergence,resonant levels,and band flatting have been addressed in improving the power factor.Additionally,phonon scattering engineerings,such as atomic-scale,nano-scale,meso-scale,and multi-scale phonon scatterings have been applied to reduce the thermal conductivity.Besides,some successful synergistic effects based on band engineerings and phonon scatterings are illustrated as a simultaneous way to optimize both the power factor and thermal conductivity.Summarizing the above three main parts,we point out that the synergistic effects should be effectively exploited,and these may further boost the thermoelectric performance of Pb Te alloys and can be extended to other thermoelectric materials.展开更多
Strontium titanate(SrTiO3) is a promising n-type material for thermoelectric applications. However, its relatively high thermal conductivity limits its performance in efficiently converting heat into electrical powe...Strontium titanate(SrTiO3) is a promising n-type material for thermoelectric applications. However, its relatively high thermal conductivity limits its performance in efficiently converting heat into electrical power through thermoelectric effect.This work shows that the thermal conductivity of SrTiO3 can be effectively reduced by annealing treatments, through an integrated study of laser flash measurement, scanning electron microscopy, Fourier transform infrared spectroscopy, x-ray absorption fine structure, and first-principles calculations. A phonon scattering model is proposed to explain the reduction of thermal conductivity after annealing. This work suggests a promising means to characterize and optimize the material for thermoelectric applications.展开更多
Lattice thermal conductivity(LTC)of cadmium arsenide(Cd_(3)As_(2))is studied over a wide temperature range(1–400 K)by employing the Callaway model.The acoustic phonons are considered to be the major carriers of heat ...Lattice thermal conductivity(LTC)of cadmium arsenide(Cd_(3)As_(2))is studied over a wide temperature range(1–400 K)by employing the Callaway model.The acoustic phonons are considered to be the major carriers of heat and to be scattered by the sample boundaries,disorder,impurities,and other phonons via both Umklapp and normal phonon processes.Numerical calculations of LTC of Cd_(3)As_(2)bring out the relative importance of the scattering mechanisms.Our systematic analysis of recent experimental data on thermal conductivity(TC)of Cd_(3)As_(2)samples of different groups,presented in terms of LTC,κL,using a nonlinear regression method,reveals good fits to the TC data of the samples considered for T<~50 K,and suggests a value of 0.2 for the Gruneisen parameter.It is,however,found that for T>100 K the inclusion of the electronic component of TC,κe,incorporating contributions from relevant electron scattering mechanisms,is needed to obtain good agreement with the TC data over the wide temperature range.More detailed investigations of TC of Cd_(3)As_(2)are required to better understand its suitability in thermoelectric and thermal management devices.展开更多
In this work,we report that the thermoelectric properties of Bi(0.52)Sb(1.48)Te3alloy can be enhanced by being composited with Mn Te nano particles(NPs)through a combined ball milling and spark plasma sintering...In this work,we report that the thermoelectric properties of Bi(0.52)Sb(1.48)Te3alloy can be enhanced by being composited with Mn Te nano particles(NPs)through a combined ball milling and spark plasma sintering(SPS)process.The addition of Mn Te into the host can synergistically reduce the lattice thermal conductivity by increasing the interface phononscattering between Bi(0.52)Sb(1.48)Te3 and MnTe NPs,and enhance the electrical transport properties by optimizing the hole concentration through partial Mn^2+ acceptor doping on the Bi^3+ sites of the host lattice.It is observed that the lattice thermal conductivity decreases with increasing the percentage of Mn Te and milling time in a temperature range from 300 Kto 500 K,which is consistent with the increasing of interfaces.Meanwhile,the bipolar effect is constrained to high temperatures,which results in the figure of merit z T peak shifting toward higher temperature and broadening the z T curves.The engineering z T is obtained to be 20%higher than that of the pristine sample for the 2-mol%Mn Te-added composite at a temperature gradient of 200 K when the cold end temperature is set to be 300 K.This result indicates that the thermoelectric performance of Bi0.52Sb1.48Te3 can be considerably enhanced by being composited with Mn Te NPs.展开更多
Recently,off-centering behavior has been discovered in a series of thermoelectric materials.This behavior indicates that the constituent atoms of the lattice displace from their coordination centers,leading to the loc...Recently,off-centering behavior has been discovered in a series of thermoelectric materials.This behavior indicates that the constituent atoms of the lattice displace from their coordination centers,leading to the locally distorted state and local symmetry breaking,while the material still retains its original crystallographic symmetry.This effect has been proved to be the root cause of ultralow thermal conductivity in off-centering materials,and is considered as an effective tool to regulate the thermal conductivity and improve the thermoelectric performance.Herein,we present a collection of recently discovered off-centering compounds,discuss their electronic origins and local coordination structures,and illuminate the underlying mechanism of the off-centering effect on phonon transport and thermal conductivity.This paper presents a comprehensive view of our current understanding to the off-centering effect,and provides a new idea for designing high performance thermoelectrics.展开更多
We report physics based confirmation(~1% RMS deviation), by existing experimental data, of protonprohol(proton-hole) ion product(p H) and mobilities in pure liquid water(0-100℃, 1-atm pressure) anticipated fr...We report physics based confirmation(~1% RMS deviation), by existing experimental data, of protonprohol(proton-hole) ion product(p H) and mobilities in pure liquid water(0-100℃, 1-atm pressure) anticipated from our melted-ice Hexagonal-Close-Packed(H_2O)_4Lattice Model. Five phonons are identified.(1) A propagating protonic phonon(520.9 meV from lone-pair-blue-shifted stretching mode of isolated water molecule) absorbed to generate a proton-prohol pair or detrap a tightly-bound proton.(2) Two(173.4 and 196.6 meV) bending-breathing protonic-proholic or protonic phonons absorbed during de-trapping-limited proton or proton-prohol mobilities.(3)Two propagating oxygenic-wateric Debye-Dispersive phonons(30.3 and 27.5 meV) absorbed during scatteringlimited proton or proton-prohol mobilities.展开更多
SiGe is recognised as an excellent thermoelectric material with superior mechanical properties and thermal stability in regions with high temperatures.This study explores a novel strategy for coregulating thermoelectr...SiGe is recognised as an excellent thermoelectric material with superior mechanical properties and thermal stability in regions with high temperatures.This study explores a novel strategy for coregulating thermoelectric transport parameters to achieve high thermoelectric properties of p-type SiGe in the mid-temperature region by incorporating nano-TaC into SiGe combined ball milling with spark plasma sintering.By optimizing the amount of TaC in the SiGe matrix,the power factors were significantly increased due to the modulation doping effect based on the work function matching of SiGe with TaC.Simultaneously,the ensemble effect of the nanostructure leads to a significant decrease in thermal conductivity.Thus,a high ZT of 1.06 was accomplished at 873 K,which is 64%higher than that of typical radioisotope thermoelectric generator.Our research offers a novel strategy for expanding and enhancing the thermoelectric properties of SiGe materials in the medium temperature range.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
It is common sense that a phase interface(or grain boundary)could be used to scatter phonons in thermoelectric(TE)materials,resulting in low thermal conductivity(k).However,a large number of impurity phases are always...It is common sense that a phase interface(or grain boundary)could be used to scatter phonons in thermoelectric(TE)materials,resulting in low thermal conductivity(k).However,a large number of impurity phases are always so harmful to the transport of carriers that poor TE performance is obtained.Here,we demonstrate that numerous superior multiphase(AgCuTe,Ag_(−2)Te,copper telluride(Cu_(2)Te and Cu_(2−x)Te),and nickel telluride(NiTe))interfaces with simultaneous strong phonon scattering and weak electron scattering could be realized in AgCuTe-based TE materials.Owing to the similar chemical bonds in these phases,the depletion region at phase interfaces,which acts as carrier scattering centers,could be ignored.Therefore,the power factor(PF)is obviously enhanced from~609 to~832μW·m^(−1)·K^(−2),and k is simultaneously decreased from~0.52 to~0.43 W·m^(−1)·K^(−1) at 636 K.Finally,a peak figure of merit(zT)of~1.23 at 636 K and an average zT(zTavg)of~1.12 in the temperature range of 523–623 K are achieved,which are one of the best values among the AgCuTe-based TE materials.This study could provide new guidance to enhance the performance by designing superior multiphase interfaces in the TE materials.展开更多
We present the work about the initiative fabrication of multi-scale hierarchical TiO2-x by our strategy,combining high pressure and high temperature(HPHT)reactive sintering with appropriate ratio of coarse Ti to nanos...We present the work about the initiative fabrication of multi-scale hierarchical TiO2-x by our strategy,combining high pressure and high temperature(HPHT)reactive sintering with appropriate ratio of coarse Ti to nanosized TiO_(2).Ubiquitous lattice defects engineering has also been achieved in our samples by HPHT.The thermoelectric performance was significantly enhanced,and rather low thermal conductivity(1.60 W m^(-1)K^(-1))for titanium oxide was reported here for TiO1.76.Correspondingly,a high dimensionless figure of merit(zT)up to 0.33 at 700℃was realized in it.As far as we know,this value is an enhancement of 43%of the ever best result about nonstoichiometric TiO_(2)and the result is also exciting for oxide thermoelectric materials.The moderate power factor,the significantly reduced thermal conductivity and the remarkable synergy between electrical properties and thermal conductivity are responsible for the excellent thermoelectric performance.We develop a facile strategy for preparing multi-scale hierarchical TiO_(2-x)and its superior ability to optimize thermoelectric performance has been demonstrated here.展开更多
Heat transport has various applications in solid materials.In particular,the thermoelectric technology provides an alternative approach to traditional methods for waste heat recovery and solid-state refrigeration by e...Heat transport has various applications in solid materials.In particular,the thermoelectric technology provides an alternative approach to traditional methods for waste heat recovery and solid-state refrigeration by enabling direct and reversible conversion between heat and electricity.For enhancing the thermoelectric performance of the materials,attempts must be made to slow down the heat transport by minimizing their thermal conductivity(κ).In this study,a continuously developing heat transport model is reviewed first.Theoretical models for predicting the lattice thermal conductivity(κlat)of materials are summarized,which are significant for the rapid screening of thermoelectric materials with lowκlat.Moreover,typical strategies,including the introduction of extrinsic phonon scattering centers with multidimensions and internal physical mechanisms of materials with intrinsically lowκlat,for slowing down the heat transport are outlined.Extrinsic defect centers with multidimensions substantially scatter various-frequency phonons;the intrinsically lowκlat in materials with various crystal structures can be attributed to the strong anharmonicity resulting from weak chemical bonding,resonant bonding,low-lying optical modes,liquid-like sublattices,off-center atoms,and complex crystal structures.This review provides an overall understanding of heat transport in thermoelectric materials and proposes effective approaches for slowing down the heat transport to depressκlat for the enhancement of thermoelectric performance.展开更多
Secondary phase Bi_(2)O_(3),which could promote the sintering densification of ceramics,was used to prepare(Ca_(0.85)Ag_(0.1)La_(0.05))_(3)Co_(4)O_(9) thermoelectric ceramics.The mechanism of liquidphase sintering pr...Secondary phase Bi_(2)O_(3),which could promote the sintering densification of ceramics,was used to prepare(Ca_(0.85)Ag_(0.1)La_(0.05))_(3)Co_(4)O_(9) thermoelectric ceramics.The mechanism of liquidphase sintering process revealed that the diffusion rate of particles originated from the dissolvedeprecipitated processing for samples and suppressed the coarsening of grain growth.The effects of Bi_(2)O_(3) on the microstructure and thermoelectric properties were investigated.The results showed that the relative density of samples increased from 92.1% to 95.5% through the liquidphase sintering mechanism.The band gaps were tuned and it had the profound impact on the transport of charge carriers.Electrical resistivity decreased while Seebeck coefficient increased from 110 mV/K to 190 mV/K with increasing Bi_(2)O_(3).Furthermore,the peak ZT value of 0.25 for 6 wt% Bi_(2)O_(3) sample at 1073 K was obtained,resulting from low thermal conductivity of 0.92 W/(m·K).It suggests that Bi_(2)O_(3) additive can dramatically improve the thermoelectric properties of Ca_(3)Co_(4)O_(9).展开更多
基金supported in part by the Grainger Center for Electric Machinery and Electromechanics of the University of Illinois
文摘We theoretically present the intrinsic limits to electron mobility in the modulation-doped AIGaN/GaN two-dimensional electron gas (2DEG) due to effects including acoustic deformation potential (DP) scattering, piezoelectric scattering (PE), and polar-optic phonon scattering (POP). We find that DE and PE are the more significant limiting factors at intermediate temperatures of 40 K to 250 K, while POP becomes dominant as room temperature is approached. Detailed numerical results are presented for the change of electron mobility with respect to temperature and carrier density. We conclude that these three types of phonon scattering, which are generally determined by the material properties but not the technical processing, are hard limits to the 2DEG mobility.
基金the Graduate Scientific Research and Innovation Foundation of Chongqing,China(No.CYB 19064)the National Natural Science Foundation of China(Nos.51772035,11674040,51472036 and 51672270)+4 种基金the Fundamental Research Funds for the Central Universities(No.106112017CDJQJ308821)the Key Research Program of Frontier Sciences,CAS(No.QYZDB-SSW-SLH016)the CSC Scholarship(No.201806050180)2019 ITS Summer Fellowship,the Natural Science Foundation of Chongqing,China(No.cstc2019jcyj-msxmX0554)the Starting Research Fund from Chongqing University。
文摘Known as a weak topological insulator(TI),BiSe structurally exhibits alternating stacks of quantum spin Hall bilayer("Bi_(2)")and three-dimensional TI layer("Bi_(2)Se_(3)").The low lattice thermal conductivity of BiSe due to the presence of Bi2 bilayers promises potentially good thermoelectric performance.Herein,the thermoelectric properties of nominal Bi_(1-x)Cu_(x)Se samples were studied as the functions of the content of Cu additive and temperature.It is found that Cu additives in BiSe(1)profoundly affect the texture of densified polycrystalline samples by inclining the crystallographic c-axis parallel toward the pressure direction in the densification process,(2)increase considerably the effective mass and thus the Seebeck coefficient,and(3)yield point defects and Cu-Se secondary phases that effectively scatter heat-carrying phonons.As a result,the optimized electrical and thermal properties yield a thermoelectric figure of merit of zT~0.29 in Bi_(1-x)Cu_(x)Se(x=0.03)sample at 467 K in parallel to the pressure direction and a zT~0.20 at 468 K in the perpendicular direction.
基金National Key Research and Development Program of China(Grant No.2017YFA0206000)eijing Natural Science Foundation(Grant No.Z180011)+1 种基金National Science Foundation of China(Grant Nos.12027807,12104241 and 61521004)roject funded by China Postdoctoral Science Foundation(Grant No.2019M660283)。
文摘Two dimensional excitonic devices are of great potential to overcome the dilemma of response time and integration in current generation of electron or/and photon based systems.The ultrashort diffusion length of exciton arising from ultrafast relaxation and low carrier mobility greatly discounts the performance of excitonic devices.Phonon scattering and exciton localization are crucial to understand the modulation of exciton flux in two dimensional disorder energy landscape,which still remain elusive.Here,we report an optimized scheme for exciton diffusion and relaxation dominated by phonon scattering and disorder potentials in WSe2 monolayers.The effective diffusion coefficient is enhanced by>200%at 280 K.The excitons tend to be localized by disorder potentials accompanied by the steadily weakening of phonon scattering when temperature drops to 260 K,and the onset of exciton localization brings forward as decreasing temperature.These findings identify that phonon scattering and disorder potentials are of great importance for long-range exciton diffusion and thermal management in exciton based systems,and lay a firm foundation for the development of functional excitonic devices.
基金Supported by the National Natural Science Foundation of China under Grant Nos U1262112 and 51176205
文摘The heat conduction and thermal conductivity for methane hydrate are simulated from equilibrium molecular dynamics. The thermal conductivity and temperature dependence trend agree well with the experimental results. The nonmonotonic temperature dependence is attributed to the phonon inelastic scattering at higher temperature and to the confinement of the optic phonon modes and low frequency phonons at low temperature. The thermal conductivity scales proportionally with the van der Waals interaction strength, The conversion of a crystal-like nature into an amorphous one oecurs at higher strength. Both the temperature dependence and interaction strength dependence are explained by phonon inelastic scattering.
文摘This paper introduces a new method for a formula for electron spin relaxation time of a system of electrons interacting with phonons through phonon-modulated spin-orbit coupling using the projection-reduction method. The phonon absorption and emission processes as well as the photon absorption and emission processes in all electron transition processes can be explained in an organized manner, and the result can be represented in a diagram that can provide intuition for the quantum dynamics of electrons in a solid. The temperature (T) dependence of electron spin relaxation times (T1) in silicon is T1 ∝ T-1.07 at low temperatures and T1 ∝ T-3.3 at high temperatures for acoustic deformation constant Pad = 1.4 × 10^7 eV and optical deformation constant Pod = 4.0 × 10^17 eV/m. This means that electrons are scattered by the acoustic deformation phonons at low temperatures and optical deformation phonons at high temperatures, respectively. The magnetic field (B) dependence of the relaxation times is T1 ∝ B-2.7 at 100 K and T1 ∝ B-2.3 at 150 K, which nearly agree with the result of Yafet, T1 ∝ B-3.0- B -2.5.
基金Project supported by the National Basic Research Program of China(Grant No.2012CB921701)the National Natural Science Foundation of China(Grant Nos.11174367 and 11004243)+4 种基金the China Postdoctoral Science Foundationthe Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(Grant Nos.10XNI03814XNLF06and 14XNLQ03)
文摘Multiferroic materials are promising candidates for next-generation multi-functional devices, because of the coexistence of multi-orders and the coupling between the orders. FeVO4 has been confirmed to be a multiferroic compound,since it exhibits both ferroelectricity and antiferromagnetic ordering at low temperatures. In this paper, we have performed careful Raman scattering measurements on high-quality Fe VO4 single crystals. The compound has a very rich phonon structure due to its low crystal symmetry(P- 1) and at least 47 Raman-active phonon modes have been resolved in the low and hightemperature spectra. Most of the observed modes are well assigned with aid of first-principles calculations and symmetry analysis. The present study provides an experimental basis for exploring spin-lattice coupling and the mechanism of multiferroicity in FeVO4
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61574109 and 61204092)
文摘Trap-assisted tunneling(TAT) has attracted more and more attention, because it seriously affects the sub-threshold characteristic of tunnel field-effect transistor(TFET). In this paper, we assess subthreshold performance of double gate TFET(DG-TFET) through a band-to-band tunneling(BTBT) model, including phonon-assisted scattering and acoustic surface phonons scattering. Interface state density profile(D_(it)) and the trap level are included in the simulation to analyze their effects on TAT current and the mechanism of gate leakage current.
基金Project supported by the Australian Research CouncilZhi-Gang Chen thanks the USQ start-up grantstrategic research grant
文摘Thermoelectric materials,enabling the directing conversion between heat and electricity,are one of the promising candidates for overcoming environmental pollution and the upcoming energy shortage caused by the over-consumption of fossil fuels.Bi2Te3-based alloys are the classical thermoelectric materials working near room temperature.Due to the intensive theoretical investigations and experimental demonstrations,significant progress has been achieved to enhance the thermoelectric performance of Bi2Te3-based thermoelectric materials.In this review,we first explored the fundamentals of thermoelectric effect and derived the equations for thermoelectric properties.On this basis,we studied the effect of material parameters on thermoelectric properties.Then,we analyzed the features of Bi2Te3-based thermoelectric materials,including the lattice defects,anisotropic behavior and the strong bipolar conduction at relatively high temperature.Then we accordingly summarized the strategies for enhancing the thermoelectric performance,including point defect engineering,texture alignment,and band gap enlargement.Moreover,we highlighted the progress in decreasing thermal conductivity using nanostructures fabricated by solution grown method,ball milling,and melt spinning.Lastly,we employed modeling analysis to uncover the principles of anisotropy behavior and the achieved enhancement in Bi2Te3,which will enlighten the enhancement of thermoelectric performance in broader materials
基金Project supported by the National Basic Research Program of China(Grant No.2013CB632506)the National Natural Science Foundation of China(Grant Nos.51501105,51672159,and 51611540342)+4 种基金the Young Scholars Program of Shandong University(Grant No.2015WLJH21)the China Postdoctoral Science Foundation(Grant Nos.2015M580588 and 2016T90631)the Postdoctoral Innovation Foundation of Shandong Province,China(Grant No.201603027)the Fundamental Research Funds of Shandong University(Grant No.2015TB019)the Foundation of the State Key Laboratory of Metastable Materials Science and Technology(Grant No.201703)
文摘The thermoelectric materials have been considered as a potential candidate for the new power generation technology based on their reversible heat and electricity conversion.Lead telluride(Pb Te) is regarded as an excellent mid-temperature thermoelectric material due to its suitable intrinsic thermoelectric properties.So tremendous efforts have been done to improve the thermoelectric performance of Pb Te,and figures of merit,zT 〉 2.0,have been reported.Main strategies for optimizing the thermoelectric performance have been focused as the main line of this review.The band engineering and phonon scattering engineering as two main effective strategies are systemically summarized here.The band engineering,like band convergence,resonant levels,and band flatting have been addressed in improving the power factor.Additionally,phonon scattering engineerings,such as atomic-scale,nano-scale,meso-scale,and multi-scale phonon scatterings have been applied to reduce the thermal conductivity.Besides,some successful synergistic effects based on band engineerings and phonon scatterings are illustrated as a simultaneous way to optimize both the power factor and thermal conductivity.Summarizing the above three main parts,we point out that the synergistic effects should be effectively exploited,and these may further boost the thermoelectric performance of Pb Te alloys and can be extended to other thermoelectric materials.
基金supported by the National Natural Science Foundation of China(Grant Nos.U1332105,51475396,11335006,21103109,21176152,and 21373137)the Natural Science Foundation of Fujian Province of China(Grant No.2013J01026)the Fundamental Research Funds for Central Universities of China(Grant Nos.2013121012,20720140517,20720160013,and 20720160020)
文摘Strontium titanate(SrTiO3) is a promising n-type material for thermoelectric applications. However, its relatively high thermal conductivity limits its performance in efficiently converting heat into electrical power through thermoelectric effect.This work shows that the thermal conductivity of SrTiO3 can be effectively reduced by annealing treatments, through an integrated study of laser flash measurement, scanning electron microscopy, Fourier transform infrared spectroscopy, x-ray absorption fine structure, and first-principles calculations. A phonon scattering model is proposed to explain the reduction of thermal conductivity after annealing. This work suggests a promising means to characterize and optimize the material for thermoelectric applications.
基金supported by University Grants Commission(UGC),India。
文摘Lattice thermal conductivity(LTC)of cadmium arsenide(Cd_(3)As_(2))is studied over a wide temperature range(1–400 K)by employing the Callaway model.The acoustic phonons are considered to be the major carriers of heat and to be scattered by the sample boundaries,disorder,impurities,and other phonons via both Umklapp and normal phonon processes.Numerical calculations of LTC of Cd_(3)As_(2)bring out the relative importance of the scattering mechanisms.Our systematic analysis of recent experimental data on thermal conductivity(TC)of Cd_(3)As_(2)samples of different groups,presented in terms of LTC,κL,using a nonlinear regression method,reveals good fits to the TC data of the samples considered for T<~50 K,and suggests a value of 0.2 for the Gruneisen parameter.It is,however,found that for T>100 K the inclusion of the electronic component of TC,κe,incorporating contributions from relevant electron scattering mechanisms,is needed to obtain good agreement with the TC data over the wide temperature range.More detailed investigations of TC of Cd_(3)As_(2)are required to better understand its suitability in thermoelectric and thermal management devices.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.U1601213 and 51472052)the Funds from Institute of Physics,Chinese Academy of Sciences
文摘In this work,we report that the thermoelectric properties of Bi(0.52)Sb(1.48)Te3alloy can be enhanced by being composited with Mn Te nano particles(NPs)through a combined ball milling and spark plasma sintering(SPS)process.The addition of Mn Te into the host can synergistically reduce the lattice thermal conductivity by increasing the interface phononscattering between Bi(0.52)Sb(1.48)Te3 and MnTe NPs,and enhance the electrical transport properties by optimizing the hole concentration through partial Mn^2+ acceptor doping on the Bi^3+ sites of the host lattice.It is observed that the lattice thermal conductivity decreases with increasing the percentage of Mn Te and milling time in a temperature range from 300 Kto 500 K,which is consistent with the increasing of interfaces.Meanwhile,the bipolar effect is constrained to high temperatures,which results in the figure of merit z T peak shifting toward higher temperature and broadening the z T curves.The engineering z T is obtained to be 20%higher than that of the pristine sample for the 2-mol%Mn Te-added composite at a temperature gradient of 200 K when the cold end temperature is set to be 300 K.This result indicates that the thermoelectric performance of Bi0.52Sb1.48Te3 can be considerably enhanced by being composited with Mn Te NPs.
基金supported by National Natural Science Foundation of China(52250090,52371208,51571007,51772012)the Beijing Natural Science Foundation(JQ18004),111 Project(B17002)L D Z appreciates the National Science Fund for Distinguished Young Scholars(51925101).
文摘Recently,off-centering behavior has been discovered in a series of thermoelectric materials.This behavior indicates that the constituent atoms of the lattice displace from their coordination centers,leading to the locally distorted state and local symmetry breaking,while the material still retains its original crystallographic symmetry.This effect has been proved to be the root cause of ultralow thermal conductivity in off-centering materials,and is considered as an effective tool to regulate the thermal conductivity and improve the thermoelectric performance.Herein,we present a collection of recently discovered off-centering compounds,discuss their electronic origins and local coordination structures,and illuminate the underlying mechanism of the off-centering effect on phonon transport and thermal conductivity.This paper presents a comprehensive view of our current understanding to the off-centering effect,and provides a new idea for designing high performance thermoelectrics.
文摘We report physics based confirmation(~1% RMS deviation), by existing experimental data, of protonprohol(proton-hole) ion product(p H) and mobilities in pure liquid water(0-100℃, 1-atm pressure) anticipated from our melted-ice Hexagonal-Close-Packed(H_2O)_4Lattice Model. Five phonons are identified.(1) A propagating protonic phonon(520.9 meV from lone-pair-blue-shifted stretching mode of isolated water molecule) absorbed to generate a proton-prohol pair or detrap a tightly-bound proton.(2) Two(173.4 and 196.6 meV) bending-breathing protonic-proholic or protonic phonons absorbed during de-trapping-limited proton or proton-prohol mobilities.(3)Two propagating oxygenic-wateric Debye-Dispersive phonons(30.3 and 27.5 meV) absorbed during scatteringlimited proton or proton-prohol mobilities.
基金supported by National Key Research and Development Program of China(No.2017YFE0198000,2022YFE0119100).National Natural Science Foundation of China(Grant No.U21A2054,52273285,52061009,52262032).Guangxi Science and Technology Project(Grant No.AD21220056).
文摘SiGe is recognised as an excellent thermoelectric material with superior mechanical properties and thermal stability in regions with high temperatures.This study explores a novel strategy for coregulating thermoelectric transport parameters to achieve high thermoelectric properties of p-type SiGe in the mid-temperature region by incorporating nano-TaC into SiGe combined ball milling with spark plasma sintering.By optimizing the amount of TaC in the SiGe matrix,the power factors were significantly increased due to the modulation doping effect based on the work function matching of SiGe with TaC.Simultaneously,the ensemble effect of the nanostructure leads to a significant decrease in thermal conductivity.Thus,a high ZT of 1.06 was accomplished at 873 K,which is 64%higher than that of typical radioisotope thermoelectric generator.Our research offers a novel strategy for expanding and enhancing the thermoelectric properties of SiGe materials in the medium temperature range.
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This work is supported by the National Natural Science Foundation of China(Grant Nos.52262032,52273285,51961011,52061009,and U21A2054)the National Key R&D Program of China(Grant No.2022YFE0119100)。
文摘It is common sense that a phase interface(or grain boundary)could be used to scatter phonons in thermoelectric(TE)materials,resulting in low thermal conductivity(k).However,a large number of impurity phases are always so harmful to the transport of carriers that poor TE performance is obtained.Here,we demonstrate that numerous superior multiphase(AgCuTe,Ag_(−2)Te,copper telluride(Cu_(2)Te and Cu_(2−x)Te),and nickel telluride(NiTe))interfaces with simultaneous strong phonon scattering and weak electron scattering could be realized in AgCuTe-based TE materials.Owing to the similar chemical bonds in these phases,the depletion region at phase interfaces,which acts as carrier scattering centers,could be ignored.Therefore,the power factor(PF)is obviously enhanced from~609 to~832μW·m^(−1)·K^(−2),and k is simultaneously decreased from~0.52 to~0.43 W·m^(−1)·K^(−1) at 636 K.Finally,a peak figure of merit(zT)of~1.23 at 636 K and an average zT(zTavg)of~1.12 in the temperature range of 523–623 K are achieved,which are one of the best values among the AgCuTe-based TE materials.This study could provide new guidance to enhance the performance by designing superior multiphase interfaces in the TE materials.
基金This work was supported by the National Natural Science Foundation of China(Grant No.51171070)the Project of Jilin Science and Technology Development Plan(20170101045JC)Graduate Innovation Fund of Jilin University(Project No.2016065).
文摘We present the work about the initiative fabrication of multi-scale hierarchical TiO2-x by our strategy,combining high pressure and high temperature(HPHT)reactive sintering with appropriate ratio of coarse Ti to nanosized TiO_(2).Ubiquitous lattice defects engineering has also been achieved in our samples by HPHT.The thermoelectric performance was significantly enhanced,and rather low thermal conductivity(1.60 W m^(-1)K^(-1))for titanium oxide was reported here for TiO1.76.Correspondingly,a high dimensionless figure of merit(zT)up to 0.33 at 700℃was realized in it.As far as we know,this value is an enhancement of 43%of the ever best result about nonstoichiometric TiO_(2)and the result is also exciting for oxide thermoelectric materials.The moderate power factor,the significantly reduced thermal conductivity and the remarkable synergy between electrical properties and thermal conductivity are responsible for the excellent thermoelectric performance.We develop a facile strategy for preparing multi-scale hierarchical TiO_(2-x)and its superior ability to optimize thermoelectric performance has been demonstrated here.
基金Beihang University111 Project,Grant/Award Number:B17002+4 种基金National Science Fund for Distinguished Young Scholars,Grant/Award Number:51925101National Postdoctoral Program for Innovative Talents,Grant/Award Number:BX20200028National Natural Science Foundation of China,Grant/Award Number:51772012Beijing Natural Science Foundation,Grant/Award Number:JQ18004National Key Research and Development Program of China,Grant/Award Numbers:2018YFB0703600,2018YFA0702100。
文摘Heat transport has various applications in solid materials.In particular,the thermoelectric technology provides an alternative approach to traditional methods for waste heat recovery and solid-state refrigeration by enabling direct and reversible conversion between heat and electricity.For enhancing the thermoelectric performance of the materials,attempts must be made to slow down the heat transport by minimizing their thermal conductivity(κ).In this study,a continuously developing heat transport model is reviewed first.Theoretical models for predicting the lattice thermal conductivity(κlat)of materials are summarized,which are significant for the rapid screening of thermoelectric materials with lowκlat.Moreover,typical strategies,including the introduction of extrinsic phonon scattering centers with multidimensions and internal physical mechanisms of materials with intrinsically lowκlat,for slowing down the heat transport are outlined.Extrinsic defect centers with multidimensions substantially scatter various-frequency phonons;the intrinsically lowκlat in materials with various crystal structures can be attributed to the strong anharmonicity resulting from weak chemical bonding,resonant bonding,low-lying optical modes,liquid-like sublattices,off-center atoms,and complex crystal structures.This review provides an overall understanding of heat transport in thermoelectric materials and proposes effective approaches for slowing down the heat transport to depressκlat for the enhancement of thermoelectric performance.
基金supported by the National Natural Science Foundation of China(No.51672219,5171101743,51702259)Excellent Youth Fund of the National Natural Science Foundation of China(No.11722219)+3 种基金Foundation of National High Technology Research and Development Program(No.2015AA0172)Fundamental Research Fund for the Central Universities(No.G2016KY0302)the“111”Project(No.B08040)the Research Foundation of the State Key Laboratory of Solidification Processing(NWPU),China(No.137-QP-2015).
文摘Secondary phase Bi_(2)O_(3),which could promote the sintering densification of ceramics,was used to prepare(Ca_(0.85)Ag_(0.1)La_(0.05))_(3)Co_(4)O_(9) thermoelectric ceramics.The mechanism of liquidphase sintering process revealed that the diffusion rate of particles originated from the dissolvedeprecipitated processing for samples and suppressed the coarsening of grain growth.The effects of Bi_(2)O_(3) on the microstructure and thermoelectric properties were investigated.The results showed that the relative density of samples increased from 92.1% to 95.5% through the liquidphase sintering mechanism.The band gaps were tuned and it had the profound impact on the transport of charge carriers.Electrical resistivity decreased while Seebeck coefficient increased from 110 mV/K to 190 mV/K with increasing Bi_(2)O_(3).Furthermore,the peak ZT value of 0.25 for 6 wt% Bi_(2)O_(3) sample at 1073 K was obtained,resulting from low thermal conductivity of 0.92 W/(m·K).It suggests that Bi_(2)O_(3) additive can dramatically improve the thermoelectric properties of Ca_(3)Co_(4)O_(9).