The InGaAs/InAIAs/InP high electron mobility transistor （HEM：F） structures with lattice-matched and pseudo- morphic channels are grown by gas source molecular beam epitaxy. Effects of Si ^-doping condition and grow...The InGaAs/InAIAs/InP high electron mobility transistor （HEM：F） structures with lattice-matched and pseudo- morphic channels are grown by gas source molecular beam epitaxy. Effects of Si ^-doping condition and growth interruption on the electrical properties are investigated by changing the Si-cell temperature, doping time and growth process. It is found that the optimal Si ^-doping concentration （Nd） is about 5.0 x 1012 cm-2 and the use of growth interruption has a dramatic effect on the improvement of electrical properties. The material structure and crystal interface are analyzed by secondary ion mass spectroscopy and high resolution transmission elec- tron microscopy. An InGaAs/InAiAs/InP HEMT device with a gate length of lOOnm is fabricated. The device presents good pinch-off characteristics and the kink-effect of the device is trifling. In addition, the device exhibits fT = 249 GHa and fmax 〉 400 GHz.展开更多
Femtosecond laser-induced periodic surface structures(LIPSS)have been extensively studied over the past few decades.In particular,the period and groove width of high-spatial-frequency LIPSS(HSFL)is much smaller than t...Femtosecond laser-induced periodic surface structures(LIPSS)have been extensively studied over the past few decades.In particular,the period and groove width of high-spatial-frequency LIPSS(HSFL)is much smaller than the diffraction limit,making it a useful method for efficient nanomanufacturing.However,compared with the low-spatial-frequency LIPSS(LSFL),the structure size of the HSFL is smaller,and it is more easily submerged.Therefore,the formation mechanism of HSFL is complex and has always been a research hotspot in this field.In this study,regular LSFL with a period of 760 nm was fabricated in advance on a silicon surface with two-beam interference using an 800 nm,50 fs femtosecond laser.The ultrafast dynamics of HSFL formation on the silicon surface of prefabricated LSFL under single femtosecond laser pulse irradiation were observed and analyzed for the first time using collinear pump-probe imaging method.In general,the evolution of the surface structure undergoes five sequential stages:the LSFL begins to split,becomes uniform HSFL,degenerates into an irregular LSFL,undergoes secondary splitting into a weakly uniform HSFL,and evolves into an irregular LSFL or is submerged.The results indicate that the local enhancement of the submerged nanocavity,or the nanoplasma,in the prefabricated LSFL ridge led to the splitting of the LSFL,and the thermodynamic effect drove the homogenization of the splitting LSFL,which evolved into HSFL.展开更多
The electronic structure of ferrite (tempered martensite phase) in high Co-Ni secondary hardened martensitic steel has been investigated. The local density of states (LOOS) of alloying elements in the steel displays t...The electronic structure of ferrite (tempered martensite phase) in high Co-Ni secondary hardened martensitic steel has been investigated. The local density of states (LOOS) of alloying elements in the steel displays the relationship between solid solubility and the shape of the LDOS. The bond order integral (BOI) between atoms in the steel shows that the directional bonding of the p orbital of Si or C leads to the brittleness of the steel. At last, ΣBOI between atoms demonstrate that C, Co, Mn, Cr, Mo, Si strengthen the alloyed steel through solid-solution effects.展开更多
Large undercoolings up to 395K (0.28TE) are obtained for 15g samples of Ni-32.5%Sn eutectic alloy by superheating the alloy melt to 108-700K above its eutectic temperature and consequently destroying most of the inher...Large undercoolings up to 395K (0.28TE) are obtained for 15g samples of Ni-32.5%Sn eutectic alloy by superheating the alloy melt to 108-700K above its eutectic temperature and consequently destroying most of the inherent heterogeneous nuclei. The recalcscence phenomenon and its dependence on undercooling and on crystal nuclcation and growth, as well as its relationship to solidification microstructures are studied. The crystalli/ation fraction during recalcsccnce is also calculated. Experiments reveal that recalcscence degree increases with undercooling when the latter is below a certain critical value∧Te, but it decreases as undercooling increases above A 7'( (under present conditions∧Te= 245K, i. c. 0.17TE). The greater the recalescencc degree, the larger the proportion of anomalous eutectic in solidified structures. It is inferred that anomalous eutectic is the product of rapid solidification while lamellar eutectic forms at much slower nuclcation rate and growth velocity.展开更多
Diamond, as the hardest known material, has been widely used in industrial applications as abrasives, coatings, and cutting and polishing tools, but it is restricted by several shortcomings, e.g., its low thermal and ...Diamond, as the hardest known material, has been widely used in industrial applications as abrasives, coatings, and cutting and polishing tools, but it is restricted by several shortcomings, e.g., its low thermal and chemical stability. Considerable efforts have been devoted to designing or synthesizing the diamond-like B-C-N-O compounds, which exhibit excellent mechanical property. In this paper, we review the recent theoretical design of diamond-like superhard structures at high pressure. In particular, the recently designed high symmetric phase of low-energy cubic BC3 meets the experimental observation, and clarifies the actual existence of cubic symmetric phase for the compounds formed by B-C-N-O system,besides the classical example of cubic boron nitride.展开更多
The high burn-up structure(HBS)is characterized by the grain size of 100-300 nm and a porosity of up to 20%,which is formed at the rim of the nuclear fuel pellet due to 2-3 times higher local burn-up during the in-pil...The high burn-up structure(HBS)is characterized by the grain size of 100-300 nm and a porosity of up to 20%,which is formed at the rim of the nuclear fuel pellet due to 2-3 times higher local burn-up during the in-pile irradiation.HBS is considered a new potential structure for high-performance fuels.However,it is difficult to prepare HBS by conventional sintering methods.In this study,flash sintering was used to prepare HBS using CeO_(2)as a surrogate for a preliminary investigation.A new experimental configuration for rapid sintering of CeO_(2)pellets was provided,in which the green body can be rapidly preheated and pressure-assisted by the induction heating electrodes.An insulated quartz tube was used as the die for the flash sintered samples,allowing the current to flow through the sample and providing a stable condition for applying an external pressure of approximately 5.3-7.0 MPa during flash sintering process.Using an initial electric field of 141 V cm-1 and holding for 1-7 min at the maximum current density of~98 mA mm^(-2),CeO_(2)ceramics with a grain size of 114-282 nm and a relative density of 75.4-99.7%were prepared.The densification and microstructure evolution behaviors during flash sintering in this new experimental configuration have been discussed in detail.This new experimental configuration may provide a promising approach for preparing UO_(2)ceramics and their HBS.展开更多
Growth of ln0.52Al0.48As epitaxial layers on lnP(100) substrates by molecular beam epitaxy at a wide range of arsenic overpressures (V/III flux ratios from 30 to 300) has been carried out. Analysis performed using low...Growth of ln0.52Al0.48As epitaxial layers on lnP(100) substrates by molecular beam epitaxy at a wide range of arsenic overpressures (V/III flux ratios from 30 to 300) has been carried out. Analysis performed using low-temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) shows a strong and prominent dependence of the PL and XRD linewidths on the V/III flux ratio. Under our growth conditions, both the PL and XRD linewidths exhibit a minimum point at a V/III flux ratio of 150 which corresponds to a maximum in the PL intensity and XRD intensity ratio. Flux ratios exceeding 150 result in an increase in both the PL and XRD linewidths corresponding to a reduction in their associated intensities. Room temperature Raman scattering measurements show a narrowing in the lnAs-like and AlAs-like longitudinal-optic (LO)phonon linewidths which broaden at high flux ratios, while the LO phonon frequencies exhibit a gradual reduction as the flux ratio is increased. PL spectra taken at increasing temperatures show a quenching of the main emission peak followed by the evolution of a broad lower energy emission which is possibly associated with deep lying centres. This effect is more prominent in samples grown at lower V/III flux ratios. Hall effect measurements show a gradual reduction in the mobility in correspondence to an increase in the electron concentration as the flux ratio is increased.展开更多
The practical application of room-temperature sodium-sulfur(RT Na-S)batteries is hindered by sluggish reaction kinetics and deleterious side reactions.To address these challenges,a defective carbon is designed as a su...The practical application of room-temperature sodium-sulfur(RT Na-S)batteries is hindered by sluggish reaction kinetics and deleterious side reactions.To address these challenges,a defective carbon is designed as a sulfur host through a simple temperature-controlled method.The abundant porosity and surface roughness enhance sulfur encapsulation and mitigate side reactions.Prominently,highly disordered structure facilitates the chemical adsorption towards NaPSs and accelerates sulfur conversion.Furthermore,electrochemical characterizations reveal that concentration polarization during the formation of long-chain NaPSs emerges as the key polarization and activation polarization dominates the nucleation of Na_(2)S during discharge,while they both significantly affect the formation of S_(8)/long-chain NaPSs during charge.Owing to the improved adsorption capability and electrocalatytic sites,S/CZ-900presents lower concentration polarization and activation polarization during both discharge and charge.Consequently,S/CZ-900 cathode achieves 1031,914,and 671 mAh g^(-1)at 1,2,and 5 C.The cathode with a high sulfur loading of 6.4 mg cm^(-2)delivers an impressive areal capacity of 14.3 mAh cm^(-2).Moreover,the S/CZ-900||Na/CZ-900(Al)full cell exhibits robust cycling stability,maintaining 1094 mAh g^(-1)after 40 cycles at 0.1 C.The insights provide a workable solution of metal-free carbonaceous host materials for the evolution of RT Na-S batteries.展开更多
The resistance to crack propagation at earlier stage for a high strength structural steel with certain ductility and its correlation to microstructures,stress states,deformation history and strain characteristics have...The resistance to crack propagation at earlier stage for a high strength structural steel with certain ductility and its correlation to microstructures,stress states,deformation history and strain characteristics have been investigated.The resistance to crack propagation is mainly de- termined by the plastic constrain ahead of the crack tip,the elastic energy and plastic work absorbed in the stress-strain field.These are connected with the state function of triaxial stress.The deformation history and strain characteristic during deformation of material are described by the flow line in which the deformation history and strain characteristic restrain the crack initiation at stage Ⅱ and the crack propagation at stage Ⅲ.The strain hardening rate may sensitively reflect the stress distribution and micro-fracture mechanism in the interi- or of material.展开更多
The development of high-sulfur-loading Li-S batteries is a key prerequisite for their commercial applications.This requires to surmount the huge polarization,severe polysulfide shuttling and drastic volume change caus...The development of high-sulfur-loading Li-S batteries is a key prerequisite for their commercial applications.This requires to surmount the huge polarization,severe polysulfide shuttling and drastic volume change caused by electrode thickening.High-strength polar binders are ideal for constructing robust and long-life high-loading sulfur cathodes but show very weak interfacial interaction with non-polar sulfur materials.To address this issue,this work devises a highly integrated sulfur@polydopamine/highstrength binder composite cathodes,targeting long-lasting and high-sulfur-loading Li-S batteries.The super-adhesion polydopamine(PD)can form a uniform nano-coating over the graphene/sulfur(G-S)surface and provide strong affinity to the cross-linked polyacrylamide(c-PAM)binder,thus tightly integrating sulfur with the binder network and greatly boosting the overall mechanical strength/conductivity of the electrode.Moreover,the PD coating and c-PAM binder rich in polar groups can form two effective blockades against the effusion of soluble polysulfides.As such,the 4.5 mg cm−2 sulfur-loaded G-S@PD-c-PAM cathode achieves a capacity of 480 mAh g−1 after 300 cycles at 1 C,while maintaining a capacity of 396 mAh g−1 after 50 cycles at 0.2 C when the sulfur loading rises to 9.1 mg cm−2.This work provides a system-wide concept for constructing high-loading sulfur cathodes through integrated structural design.展开更多
With TEM、SEM, various high temperature deformed structures in W9Mo3Cr4V steel were investigated. The sub structures,recrystallized nuclei, as well as the dynamic precipitation were also studied and analyzed. The r...With TEM、SEM, various high temperature deformed structures in W9Mo3Cr4V steel were investigated. The sub structures,recrystallized nuclei, as well as the dynamic precipitation were also studied and analyzed. The relationship between recrystallized structures and dynamic precipitation was discussed. The results showed that the deformed structures in W9Mo3Cr4V steel are more complicated than those in low alloy steels. Because W9Mo3Cr4V steel is a high speed steel, there are a large number of residual carbides on the matrix. Also, much dynamic precipitating carbides will precipitate during deformation at high temperature.展开更多
The layered semiconductor BaFZnAs with the tetragonal ZrCuSiAs-type structure has been successfully synthesized.Both the in-situ high-pressure synchrotron x-ray diffraction and the high-pressure Raman scattering measu...The layered semiconductor BaFZnAs with the tetragonal ZrCuSiAs-type structure has been successfully synthesized.Both the in-situ high-pressure synchrotron x-ray diffraction and the high-pressure Raman scattering measurements demonstrate that the structure of BaFZnAs is stable under pressure up to 17.5 GPa at room temperature. The resistivity and the magnetic susceptibility data show that BaFZnAs is a non-magnetic semiconductor. BaFZnAs is recommended as a candidate of the host material of diluted magnetic semiconductor.展开更多
Two kinds of compact electromagnetic band gap （EBG） structures are designed. A two layer compact EBG structure configured with cross spiral shape line inductors and interdigital capacitors is first presented. Becaus...Two kinds of compact electromagnetic band gap （EBG） structures are designed. A two layer compact EBG structure configured with cross spiral shape line inductors and interdigital capacitors is first presented. Because of its significantly enlarged equivalent inductor and capacitance, the period of the lattice is approximately 4.5% of the free space wavelength. By insetting several narrow slits in the ground plane, the bandwidth of the main bandgap is enhanced by nearly 19%. Further effort has been made for designing a three layer compact EBG structure. Simulation results show that its period is reduced by about 26% compared to that of proposed two layer EBG structure, and the bandwidth of the main bandgap is about 3 times as that of the proposed two layer EBG structure. The detailed designs including a two layer compact 3×7 EBG array with and without defect ground plane and the three layer EBG array are given and simulation results are presented.展开更多
The response of three-dimensional sample of Al, containing vacancy complex, under shear loading was simulated. The molecular dynamics method was used and interaction between atoms was described on the base of pseudopo...The response of three-dimensional sample of Al, containing vacancy complex, under shear loading was simulated. The molecular dynamics method was used and interaction between atoms was described on the base of pseudopotential theory Solitary waves were generated in the sample under mechanical loading. Their interaction with the vacancy complexes was shown to be able to initiate hot spot in that local region of the complexes. Some parameters of the hot spot as well as solitary waves were calculated. The initiation of the hot spot is accompanied with sufficient local structural relaxation.展开更多
In recent years, microstrip antennas have been more widely applied in satellite communications, mobile phones, unmanned aerial vehicle （UAV）, and weapons. A micro-electro-mechanical systems-based （MEMS-based） high...In recent years, microstrip antennas have been more widely applied in satellite communications, mobile phones, unmanned aerial vehicle （UAV）, and weapons. A micro-electro-mechanical systems-based （MEMS-based） high-resistance silicon C-band microstrip antenna array has been designed for the intelligent ammunition. The center frequency is 4.5 GHz. A cavity has been designed in substrate to reduce the dielectric constant of silicon and high-resistance silicon has been used as the material of substrate to improve the gain of antenna. It is very easy to be manufactured by using MEMS technology because of the improved structure of the antenna. The results show that the gain of the antenna is 8 dB and voltage standing wave ratio （VSWR） is less than 2 by the analysis and simulation in high freauencv structure simulator （HFSS）.展开更多
The effect of tempering on carbides and hydrogen embrittlement in E690 high strength marine structural steel has been investigated.The steel was tempered at 600℃ for 1–3 h.Detailed characterization was carried out t...The effect of tempering on carbides and hydrogen embrittlement in E690 high strength marine structural steel has been investigated.The steel was tempered at 600℃ for 1–3 h.Detailed characterization was carried out to characterize the microstructure,especially the dislocation density and grain size.The hydrogen permeation test and thermal desorption spectroscopy test were also implemented.The dislocation density decreases,the amount of carbide increases,and carbides(M_(23)C_(6) and MX)coarsen with the tempering time increasing.After tempered at 600℃ for 3 h,the diffusible hydrogen trapped by lattice and dislocation decreases while the non-diffusible hydrogen trapped by carbides increases,leading to the best hydrogen embrittlement resistance,although hydrogen diffuses rapidly due to the reduction of dislocation density.And the fracture mode changes from a combination of brittle cleavage and ductile dimpled fracture to fully ductile dimple fracture under hydrogen charging condition.Moreover,a phenomenon that hydrogen accelerates the dislocations movement of the steel during deformation was observed,which is related to the fact that hydrogen enhanced localized plasticity mechanism.展开更多
In Espírito Santo State,Brazil,between the municipalities of Vitória,Colatina and Ecoporanga,there is a mountainous region characterized by a shear zone which trends NNW-SSE and is filled by a diabase
Animal bone was employed as raw material to prepare hierarchical porous carbon by KOH activation. Rare metal selenium（Se） was encapsulated into hierarchical porous carbon successfully for the cathode material of Li...Animal bone was employed as raw material to prepare hierarchical porous carbon by KOH activation. Rare metal selenium（Se） was encapsulated into hierarchical porous carbon successfully for the cathode material of Li–Se battery, achieving the transformation of waste into energy,protecting environment and reducing the spread of the disease. Animal bone porous carbon（ABPC） acquires a specific surface area of 1244.7903 m^2·g^-1 and a pore volume of 0.594184 cm^3·g^-1. The composite Se/ABPC with 51 wt%Se was tested as a novel cathode for Li–Se batteries. The results show that Se/ABPC exhibits high specific capacity,good cycling stability and current-rate performance; at 0.1C,the composite Se/ABPC delivers a high reversible capacity of 705 mAh·g^-1 in the second cycle and 591 mAh·g^-1 after 98 cycles. Even at the current density of 2.0C, it can still maintain at a reversible capacity of 485 mAh·g^-1. The excellent electrochemical properties benefit from the high electron conductivity and the carbon with unique hierarchical porous structure. ABPC can be a promising carbon matrix for Li–Se batteries.展开更多
The work functions of the （110） and （10（3） surfaces of LaB6 are determined from ambient pressure to 39.1 GPa. The work function of the （110） surface slowly decreases but that of the （100） surface remains at a...The work functions of the （110） and （10（3） surfaces of LaB6 are determined from ambient pressure to 39.1 GPa. The work function of the （110） surface slowly decreases but that of the （100） surface remains at a relatively constant value. To determine the reason for this difference, the electron density distribution （EDD） is determined from high-pressure single-crystal x-ray diffraction data by the maximum entropy method. The EDD results show that the chemical bond properties in LaB6 play a key role also investigated by single-crystal x-ray diffraction. In observed from ambient pressure to 39.1 GPa. The structural stability of LaB6 under high pressure is this study, no structural or electronic phase transition is展开更多
The pressure-induced structural transitions of ZnTe are investigated at pressures up to 59.2 GPa in a diamond anvil cell by using synchrotron powder x-ray diffraction method. A phase transition from the initial zinc b...The pressure-induced structural transitions of ZnTe are investigated at pressures up to 59.2 GPa in a diamond anvil cell by using synchrotron powder x-ray diffraction method. A phase transition from the initial zinc blende （ZB, ZnTe-Ⅰ） structure to a cinnabar phase （ZnTe-Ⅱ） is observed at 9.6 GPa, followed by a high pressure orthorhombic phase （ZnTe-Ⅲ） with Cmcm symmetry at 12.1 GPa. The ZB, cinnabar （space group P3121）, Cmcm, P31 and rock salt structures of ZnTe are investigated by using density functional theory calculations. Based on the experiments and calculations, the ZnTe-Ⅱ phase is determined to have a cinnabar structure rather than a P3 1 symmetry.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 61434006
文摘The InGaAs/InAIAs/InP high electron mobility transistor （HEM：F） structures with lattice-matched and pseudo- morphic channels are grown by gas source molecular beam epitaxy. Effects of Si ^-doping condition and growth interruption on the electrical properties are investigated by changing the Si-cell temperature, doping time and growth process. It is found that the optimal Si ^-doping concentration （Nd） is about 5.0 x 1012 cm-2 and the use of growth interruption has a dramatic effect on the improvement of electrical properties. The material structure and crystal interface are analyzed by secondary ion mass spectroscopy and high resolution transmission elec- tron microscopy. An InGaAs/InAiAs/InP HEMT device with a gate length of lOOnm is fabricated. The device presents good pinch-off characteristics and the kink-effect of the device is trifling. In addition, the device exhibits fT = 249 GHa and fmax 〉 400 GHz.
基金supports from the National Natural Science Foundation of China(12074123,12174108)the Foundation of‘Manufacturing beyond limits’of Shanghai‘Talent Program'of Henan Academy of Sciences.
文摘Femtosecond laser-induced periodic surface structures(LIPSS)have been extensively studied over the past few decades.In particular,the period and groove width of high-spatial-frequency LIPSS(HSFL)is much smaller than the diffraction limit,making it a useful method for efficient nanomanufacturing.However,compared with the low-spatial-frequency LIPSS(LSFL),the structure size of the HSFL is smaller,and it is more easily submerged.Therefore,the formation mechanism of HSFL is complex and has always been a research hotspot in this field.In this study,regular LSFL with a period of 760 nm was fabricated in advance on a silicon surface with two-beam interference using an 800 nm,50 fs femtosecond laser.The ultrafast dynamics of HSFL formation on the silicon surface of prefabricated LSFL under single femtosecond laser pulse irradiation were observed and analyzed for the first time using collinear pump-probe imaging method.In general,the evolution of the surface structure undergoes five sequential stages:the LSFL begins to split,becomes uniform HSFL,degenerates into an irregular LSFL,undergoes secondary splitting into a weakly uniform HSFL,and evolves into an irregular LSFL or is submerged.The results indicate that the local enhancement of the submerged nanocavity,or the nanoplasma,in the prefabricated LSFL ridge led to the splitting of the LSFL,and the thermodynamic effect drove the homogenization of the splitting LSFL,which evolved into HSFL.
文摘The electronic structure of ferrite (tempered martensite phase) in high Co-Ni secondary hardened martensitic steel has been investigated. The local density of states (LOOS) of alloying elements in the steel displays the relationship between solid solubility and the shape of the LDOS. The bond order integral (BOI) between atoms in the steel shows that the directional bonding of the p orbital of Si or C leads to the brittleness of the steel. At last, ΣBOI between atoms demonstrate that C, Co, Mn, Cr, Mo, Si strengthen the alloyed steel through solid-solution effects.
文摘Large undercoolings up to 395K (0.28TE) are obtained for 15g samples of Ni-32.5%Sn eutectic alloy by superheating the alloy melt to 108-700K above its eutectic temperature and consequently destroying most of the inherent heterogeneous nuclei. The recalcscence phenomenon and its dependence on undercooling and on crystal nuclcation and growth, as well as its relationship to solidification microstructures are studied. The crystalli/ation fraction during recalcsccnce is also calculated. Experiments reveal that recalcscence degree increases with undercooling when the latter is below a certain critical value∧Te, but it decreases as undercooling increases above A 7'( (under present conditions∧Te= 245K, i. c. 0.17TE). The greater the recalescencc degree, the larger the proportion of anomalous eutectic in solidified structures. It is inferred that anomalous eutectic is the product of rapid solidification while lamellar eutectic forms at much slower nuclcation rate and growth velocity.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51202084,11474125,and 51372095)
文摘Diamond, as the hardest known material, has been widely used in industrial applications as abrasives, coatings, and cutting and polishing tools, but it is restricted by several shortcomings, e.g., its low thermal and chemical stability. Considerable efforts have been devoted to designing or synthesizing the diamond-like B-C-N-O compounds, which exhibit excellent mechanical property. In this paper, we review the recent theoretical design of diamond-like superhard structures at high pressure. In particular, the recently designed high symmetric phase of low-energy cubic BC3 meets the experimental observation, and clarifies the actual existence of cubic symmetric phase for the compounds formed by B-C-N-O system,besides the classical example of cubic boron nitride.
基金The work was financially supported by the National Natural Science Foundation of China(Nos.51874023,U1860206)the Fundamental Research Funds for the Central Universities(No.FRF-TP-20-02B)the Recruitment Program of Global Experts.
文摘The high burn-up structure(HBS)is characterized by the grain size of 100-300 nm and a porosity of up to 20%,which is formed at the rim of the nuclear fuel pellet due to 2-3 times higher local burn-up during the in-pile irradiation.HBS is considered a new potential structure for high-performance fuels.However,it is difficult to prepare HBS by conventional sintering methods.In this study,flash sintering was used to prepare HBS using CeO_(2)as a surrogate for a preliminary investigation.A new experimental configuration for rapid sintering of CeO_(2)pellets was provided,in which the green body can be rapidly preheated and pressure-assisted by the induction heating electrodes.An insulated quartz tube was used as the die for the flash sintered samples,allowing the current to flow through the sample and providing a stable condition for applying an external pressure of approximately 5.3-7.0 MPa during flash sintering process.Using an initial electric field of 141 V cm-1 and holding for 1-7 min at the maximum current density of~98 mA mm^(-2),CeO_(2)ceramics with a grain size of 114-282 nm and a relative density of 75.4-99.7%were prepared.The densification and microstructure evolution behaviors during flash sintering in this new experimental configuration have been discussed in detail.This new experimental configuration may provide a promising approach for preparing UO_(2)ceramics and their HBS.
文摘Growth of ln0.52Al0.48As epitaxial layers on lnP(100) substrates by molecular beam epitaxy at a wide range of arsenic overpressures (V/III flux ratios from 30 to 300) has been carried out. Analysis performed using low-temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) shows a strong and prominent dependence of the PL and XRD linewidths on the V/III flux ratio. Under our growth conditions, both the PL and XRD linewidths exhibit a minimum point at a V/III flux ratio of 150 which corresponds to a maximum in the PL intensity and XRD intensity ratio. Flux ratios exceeding 150 result in an increase in both the PL and XRD linewidths corresponding to a reduction in their associated intensities. Room temperature Raman scattering measurements show a narrowing in the lnAs-like and AlAs-like longitudinal-optic (LO)phonon linewidths which broaden at high flux ratios, while the LO phonon frequencies exhibit a gradual reduction as the flux ratio is increased. PL spectra taken at increasing temperatures show a quenching of the main emission peak followed by the evolution of a broad lower energy emission which is possibly associated with deep lying centres. This effect is more prominent in samples grown at lower V/III flux ratios. Hall effect measurements show a gradual reduction in the mobility in correspondence to an increase in the electron concentration as the flux ratio is increased.
基金financially supported by the National Natural Science Foundation of China(51977071)the Natural Science Foundation of Hunan Province(2017JJ2040)the Science and Technology Innovation Program of Hunan Province(2021RC3066)。
文摘The practical application of room-temperature sodium-sulfur(RT Na-S)batteries is hindered by sluggish reaction kinetics and deleterious side reactions.To address these challenges,a defective carbon is designed as a sulfur host through a simple temperature-controlled method.The abundant porosity and surface roughness enhance sulfur encapsulation and mitigate side reactions.Prominently,highly disordered structure facilitates the chemical adsorption towards NaPSs and accelerates sulfur conversion.Furthermore,electrochemical characterizations reveal that concentration polarization during the formation of long-chain NaPSs emerges as the key polarization and activation polarization dominates the nucleation of Na_(2)S during discharge,while they both significantly affect the formation of S_(8)/long-chain NaPSs during charge.Owing to the improved adsorption capability and electrocalatytic sites,S/CZ-900presents lower concentration polarization and activation polarization during both discharge and charge.Consequently,S/CZ-900 cathode achieves 1031,914,and 671 mAh g^(-1)at 1,2,and 5 C.The cathode with a high sulfur loading of 6.4 mg cm^(-2)delivers an impressive areal capacity of 14.3 mAh cm^(-2).Moreover,the S/CZ-900||Na/CZ-900(Al)full cell exhibits robust cycling stability,maintaining 1094 mAh g^(-1)after 40 cycles at 0.1 C.The insights provide a workable solution of metal-free carbonaceous host materials for the evolution of RT Na-S batteries.
文摘The resistance to crack propagation at earlier stage for a high strength structural steel with certain ductility and its correlation to microstructures,stress states,deformation history and strain characteristics have been investigated.The resistance to crack propagation is mainly de- termined by the plastic constrain ahead of the crack tip,the elastic energy and plastic work absorbed in the stress-strain field.These are connected with the state function of triaxial stress.The deformation history and strain characteristic during deformation of material are described by the flow line in which the deformation history and strain characteristic restrain the crack initiation at stage Ⅱ and the crack propagation at stage Ⅲ.The strain hardening rate may sensitively reflect the stress distribution and micro-fracture mechanism in the interi- or of material.
基金supported by the National Natural Science Foundation of China(21875155,51675275,21703185 and 21473119)Q.B.Z.acknowledges the Leading Project Foundation of Science Department of Fujian Province(2018H0034)Shenzhen Science and Technology Planning Project(JCYJ20170818153427106).
文摘The development of high-sulfur-loading Li-S batteries is a key prerequisite for their commercial applications.This requires to surmount the huge polarization,severe polysulfide shuttling and drastic volume change caused by electrode thickening.High-strength polar binders are ideal for constructing robust and long-life high-loading sulfur cathodes but show very weak interfacial interaction with non-polar sulfur materials.To address this issue,this work devises a highly integrated sulfur@polydopamine/highstrength binder composite cathodes,targeting long-lasting and high-sulfur-loading Li-S batteries.The super-adhesion polydopamine(PD)can form a uniform nano-coating over the graphene/sulfur(G-S)surface and provide strong affinity to the cross-linked polyacrylamide(c-PAM)binder,thus tightly integrating sulfur with the binder network and greatly boosting the overall mechanical strength/conductivity of the electrode.Moreover,the PD coating and c-PAM binder rich in polar groups can form two effective blockades against the effusion of soluble polysulfides.As such,the 4.5 mg cm−2 sulfur-loaded G-S@PD-c-PAM cathode achieves a capacity of 480 mAh g−1 after 300 cycles at 1 C,while maintaining a capacity of 396 mAh g−1 after 50 cycles at 0.2 C when the sulfur loading rises to 9.1 mg cm−2.This work provides a system-wide concept for constructing high-loading sulfur cathodes through integrated structural design.
基金Project Sponsored by Ministry of Science and Technology of China(G1998061513)
文摘With TEM、SEM, various high temperature deformed structures in W9Mo3Cr4V steel were investigated. The sub structures,recrystallized nuclei, as well as the dynamic precipitation were also studied and analyzed. The relationship between recrystallized structures and dynamic precipitation was discussed. The results showed that the deformed structures in W9Mo3Cr4V steel are more complicated than those in low alloy steels. Because W9Mo3Cr4V steel is a high speed steel, there are a large number of residual carbides on the matrix. Also, much dynamic precipitating carbides will precipitate during deformation at high temperature.
基金Project supported by the National Natural Science Foundation of ChinaProject of Ministry of Science and Technology of China
文摘The layered semiconductor BaFZnAs with the tetragonal ZrCuSiAs-type structure has been successfully synthesized.Both the in-situ high-pressure synchrotron x-ray diffraction and the high-pressure Raman scattering measurements demonstrate that the structure of BaFZnAs is stable under pressure up to 17.5 GPa at room temperature. The resistivity and the magnetic susceptibility data show that BaFZnAs is a non-magnetic semiconductor. BaFZnAs is recommended as a candidate of the host material of diluted magnetic semiconductor.
基金supported by the National Natural Science Foundation of China under Grant No. 60588502
文摘Two kinds of compact electromagnetic band gap （EBG） structures are designed. A two layer compact EBG structure configured with cross spiral shape line inductors and interdigital capacitors is first presented. Because of its significantly enlarged equivalent inductor and capacitance, the period of the lattice is approximately 4.5% of the free space wavelength. By insetting several narrow slits in the ground plane, the bandwidth of the main bandgap is enhanced by nearly 19%. Further effort has been made for designing a three layer compact EBG structure. Simulation results show that its period is reduced by about 26% compared to that of proposed two layer EBG structure, and the bandwidth of the main bandgap is about 3 times as that of the proposed two layer EBG structure. The detailed designs including a two layer compact 3×7 EBG array with and without defect ground plane and the three layer EBG array are given and simulation results are presented.
文摘The response of three-dimensional sample of Al, containing vacancy complex, under shear loading was simulated. The molecular dynamics method was used and interaction between atoms was described on the base of pseudopotential theory Solitary waves were generated in the sample under mechanical loading. Their interaction with the vacancy complexes was shown to be able to initiate hot spot in that local region of the complexes. Some parameters of the hot spot as well as solitary waves were calculated. The initiation of the hot spot is accompanied with sufficient local structural relaxation.
基金supported by the Chinese PLA General Armament Department under Grant No.51318020305
文摘In recent years, microstrip antennas have been more widely applied in satellite communications, mobile phones, unmanned aerial vehicle （UAV）, and weapons. A micro-electro-mechanical systems-based （MEMS-based） high-resistance silicon C-band microstrip antenna array has been designed for the intelligent ammunition. The center frequency is 4.5 GHz. A cavity has been designed in substrate to reduce the dielectric constant of silicon and high-resistance silicon has been used as the material of substrate to improve the gain of antenna. It is very easy to be manufactured by using MEMS technology because of the improved structure of the antenna. The results show that the gain of the antenna is 8 dB and voltage standing wave ratio （VSWR） is less than 2 by the analysis and simulation in high freauencv structure simulator （HFSS）.
基金The authors acknowledge the generous financial support from National Key R&D Program of China(No.2016YFB0300601)the National Natural Science Foundation of China(Nos.U1564203,51831002 and 51571141)+2 种基金The authors also gratefully acknowledge the support sponsored by Program of Shanghai Academic Research Leader 18XD1402200provided by Shanghai Key Laboratory of Materials Laser Processing and Modification,Shanghai Jiao Tong UniversityBesides,this research was supported by the TESCAN CHINA.
文摘The effect of tempering on carbides and hydrogen embrittlement in E690 high strength marine structural steel has been investigated.The steel was tempered at 600℃ for 1–3 h.Detailed characterization was carried out to characterize the microstructure,especially the dislocation density and grain size.The hydrogen permeation test and thermal desorption spectroscopy test were also implemented.The dislocation density decreases,the amount of carbide increases,and carbides(M_(23)C_(6) and MX)coarsen with the tempering time increasing.After tempered at 600℃ for 3 h,the diffusible hydrogen trapped by lattice and dislocation decreases while the non-diffusible hydrogen trapped by carbides increases,leading to the best hydrogen embrittlement resistance,although hydrogen diffuses rapidly due to the reduction of dislocation density.And the fracture mode changes from a combination of brittle cleavage and ductile dimpled fracture to fully ductile dimple fracture under hydrogen charging condition.Moreover,a phenomenon that hydrogen accelerates the dislocations movement of the steel during deformation was observed,which is related to the fact that hydrogen enhanced localized plasticity mechanism.
基金Repsol Sinopec Petroleum Brazil for its financial support to this interinstitutional research
文摘In Espírito Santo State,Brazil,between the municipalities of Vitória,Colatina and Ecoporanga,there is a mountainous region characterized by a shear zone which trends NNW-SSE and is filled by a diabase
基金financially supported by the National Natural Science Foundation of China(Nos.51272156,21373137 and 21333007)the City Committee of Science and Technology Project of Shanghai(No.14JC1491800)the New Century Excellent Talents in University(Nos.NCET-13-0371)
文摘Animal bone was employed as raw material to prepare hierarchical porous carbon by KOH activation. Rare metal selenium（Se） was encapsulated into hierarchical porous carbon successfully for the cathode material of Li–Se battery, achieving the transformation of waste into energy,protecting environment and reducing the spread of the disease. Animal bone porous carbon（ABPC） acquires a specific surface area of 1244.7903 m^2·g^-1 and a pore volume of 0.594184 cm^3·g^-1. The composite Se/ABPC with 51 wt%Se was tested as a novel cathode for Li–Se batteries. The results show that Se/ABPC exhibits high specific capacity,good cycling stability and current-rate performance; at 0.1C,the composite Se/ABPC delivers a high reversible capacity of 705 mAh·g^-1 in the second cycle and 591 mAh·g^-1 after 98 cycles. Even at the current density of 2.0C, it can still maintain at a reversible capacity of 485 mAh·g^-1. The excellent electrochemical properties benefit from the high electron conductivity and the carbon with unique hierarchical porous structure. ABPC can be a promising carbon matrix for Li–Se batteries.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11274030 and 11474281
文摘The work functions of the （110） and （10（3） surfaces of LaB6 are determined from ambient pressure to 39.1 GPa. The work function of the （110） surface slowly decreases but that of the （100） surface remains at a relatively constant value. To determine the reason for this difference, the electron density distribution （EDD） is determined from high-pressure single-crystal x-ray diffraction data by the maximum entropy method. The EDD results show that the chemical bond properties in LaB6 play a key role also investigated by single-crystal x-ray diffraction. In observed from ambient pressure to 39.1 GPa. The structural stability of LaB6 under high pressure is this study, no structural or electronic phase transition is
基金Supported by the National Natural Science Foundation of China under Grant No 11474280the National Basic Research Program of China under Grant No 2011CB808200the Chinese Academy of Sciences under Grant Nos KJCX2-SW-N20 and KJCX2-SW-N03
文摘The pressure-induced structural transitions of ZnTe are investigated at pressures up to 59.2 GPa in a diamond anvil cell by using synchrotron powder x-ray diffraction method. A phase transition from the initial zinc blende （ZB, ZnTe-Ⅰ） structure to a cinnabar phase （ZnTe-Ⅱ） is observed at 9.6 GPa, followed by a high pressure orthorhombic phase （ZnTe-Ⅲ） with Cmcm symmetry at 12.1 GPa. The ZB, cinnabar （space group P3121）, Cmcm, P31 and rock salt structures of ZnTe are investigated by using density functional theory calculations. Based on the experiments and calculations, the ZnTe-Ⅱ phase is determined to have a cinnabar structure rather than a P3 1 symmetry.
