LiFePO_(4)has normal olivine-structured(a-LFP)and high pressure(b-LFP)phases,with the former being one of the cathode materials for commercial Li-ion batteries.Despite extensive focus on the respective electrochemical...LiFePO_(4)has normal olivine-structured(a-LFP)and high pressure(b-LFP)phases,with the former being one of the cathode materials for commercial Li-ion batteries.Despite extensive focus on the respective electrochemical properties of the two phases,there is a lack of comparative studies on their electronic and magnetic properties,and the origin of the structural phase transition remains unclear.By combining first-principles calculations with molecular dynamics simulations,we find that the anisotropic compression of Li-O bonds drives the structural phase transition from a-LFP to b-LFP at a critical pressure of 20 GPa,while b-LFP undergoes a transition from semiconductor to metal due to Fe^(3+)generated during delithiation.Their antiferromagnetic(AFM)ground states are predicted to arise from the negative magnetic exchange interactions between nearest and next-nearest neighbor sites,with the corresponding N'eel temperature showing significant enhancement under pressure.Furthermore,compared with a-LFP,b-LFP shows increases in bulk,shear,and Young’s moduli of 8%,13%,and 12%,respectively.These findings enrich the physical property data of LiFePO_(4)phase compounds,providing knowledge for expanding the application scenarios of the a-LFP phase under special operating conditions such as high pressure.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
We investigate the electronic structures of FeSe in the presence of different possible orders and spin-orbit coupling （SOC）. It is found that only the ferro-orbital order （FO） and the collinear antiferro-magnetism...We investigate the electronic structures of FeSe in the presence of different possible orders and spin-orbit coupling （SOC）. It is found that only the ferro-orbital order （FO） and the collinear antiferro-magnetism （C-AFM） can simultaneously induce splittings at F and M. Bicollinear antiferro-magnetism （B-AFM） and SOC have very similar band structures on F-M near the Fermi level. The temperature T insensitive splitting at F and the T-dependent splitting at M observed in recent experiments can be explained by the d-wave bond nematic （dBN） order together with SOC. The recent observed Dirac cones and their T-dependence in FeSe thin films can also be well explained by the dBN order together with the band renormMization. Their thickness- and cobalt-doping- dependent behaviors are the consequences of electron doping and reduction of Se height. All these suggest that the nematic order in the FeSe system is the dBN order.展开更多
Sodium-ion batteries are the prominent device for stationary energy storage system and low-speed electric vehicles.However,the practical application is still limited by the unsatisfied performance and high cost of the...Sodium-ion batteries are the prominent device for stationary energy storage system and low-speed electric vehicles.However,the practical application is still limited by the unsatisfied performance and high cost of the cathode side,which strictly requires the development of high voltage,high capacity,and earth-abundant cathode material.Ni-Fe-Mn ternary layered oxide has been recognized as one of the most promising standard type of cathodes.However,the composition and phase structure on high-voltage characteristics have not been well investigated.Herein,selecting the typically high-voltage cathode of P2-Na_(0.67)Ni_(0.33)Mn_(0.67)O_(2)as a parent material,we fabricate ten Ni-Fe-Mn ternary layered oxides through replacing the Ni,Mn,or both Ni and Mn by Fe.The thermodynamically stable phase diagram for those materials is presented.The electrochemical properties for all the samples are investigated in detail.Three potential Ni-Fe-Mn ternary layered oxides are picked up considering the energy density,cycle stability,kinetics,cost price,and working voltage,which demonstrate great potential for surpassing the performance of lithium iron phosphate.The related electrochemical reaction and fading mechanism are well revealed.This work provides some new foundational Ni-Fe-Mn ternary layered materials for high-voltage sodium-ion batteries.展开更多
The mechanical,thermodynamic properties and electrical conductivities of L1_(2)-Al_(3)X(X=Zr,Sc,Er,Yb,Hf)structural phases in aluminum conductors were investigated through a first-principles study.The results demonstr...The mechanical,thermodynamic properties and electrical conductivities of L1_(2)-Al_(3)X(X=Zr,Sc,Er,Yb,Hf)structural phases in aluminum conductors were investigated through a first-principles study.The results demonstrate that all structural phases have good alloy-forming ability and structural stability,where Al_(3)Zr is the most superior.Al_(3)Zr,Al_(3)Hf and Al_(3)Sc have enhanced shear and deformation resistance in comparison to other phases.Within the temperature range of 200−600 K,Al_(3)Er and Al_(3)Yb possess the greatest thermodynamic stability,followed by Al_(3)Hf,Al_(3)Zr and Al_(3)Sc.Al_(3)Er and Al_(3)Yb have higher thermodynamic stability than Al_(3)Hf,Al_(3)Zr and Al_(3)Sc.All structural phases exhibit substantial metallic properties,indicating their good electrical conductivity.The electrical conductivities of Al_(3)Hf and Al_(3)Zr are higher than those of Al_(3)Er,Al_(3)Yb and Al_(3)Sc.The covalent bond properties in Al_(3)Sc,Al_(3)Er and Al_(3)Yb enhance the hardness,brittleness and thermodynamic stability of the structural phase.The thermodynamic stability of Al_(3)Sc is significantly reduced by ionic bonds.展开更多
La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75-xFex （x=0-0.20） hydrogen storage alloys were synthesized by induction melting and subsequent annealing treatment, and phase structure and electrochemical characteristics were inves...La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75-xFex （x=0-0.20） hydrogen storage alloys were synthesized by induction melting and subsequent annealing treatment, and phase structure and electrochemical characteristics were investigated. All alloys consist of a single LaNi5 phase with CaCu5 structure, and the lattice constant a and the cell volume （V） of the LaNi5 phase increase with increasing x value. The maximum discharge capacity gradually decreases from 319.0 mA？h/g （x=0） to 291.9 mA？h/g （x=0.20） with the increase in x value. The high-rate dischargeability at the discharge current density of 1200 mA/g decreases monotonically from 53.1% （x=0） to 44.2% （x=0.20）. The cycling stability increases with increasing x from 0 to 0.20, which is mainly ascribed to the improvement of the pulverization resistance.展开更多
The microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr （x=1, 2, 3, 4; normal mass fraction in %） alloys were investigated. In low Zn content, aside from the major second phase of Mg24（Er, Y, Zn）5,...The microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr （x=1, 2, 3, 4; normal mass fraction in %） alloys were investigated. In low Zn content, aside from the major second phase of Mg24（Er, Y, Zn）5, there are a few lamellar phases that grow parallel with each other from the grain boundaries to the grain interior. With Zn content increasing, the Mg24（Er, Y, Zn）5 phase decreases, but the Mg12Zn（Y, Er） phase and lamellar phases continuously increase. When Zn content reaches 4% （normal mass fraction）, the Mg12Zn（Y, Er） phase mainly exists as large bulks, and some a-Mg grains are thoroughly penetrated by the lamellar phases. Moreover, the crystallography structures of the Mgl2Zn（Y, Er） and Mg24（Er, Y, Zn）5 phases are confirmed as 18R-type long-period stacking ordered structure and body-centred cubic structure, respectively.展开更多
The effects of annealing treatment on the microstructure and electrochemical properties of low-Co LaNi 3.55 Mn 0.35 Co 0.20 Al 0.20 Cu 0.75 Fe 0.10 hydrogen storage alloys were investigated. X-ray diffraction （XRD） ...The effects of annealing treatment on the microstructure and electrochemical properties of low-Co LaNi 3.55 Mn 0.35 Co 0.20 Al 0.20 Cu 0.75 Fe 0.10 hydrogen storage alloys were investigated. X-ray diffraction （XRD） analysis indicated that annealing treatment remarkably reduced the lattice strain and defects, and increased the unit-cell volume. The optical microscope analysis showed that the as-cast alloy had a crass dendrite microstructure with noticeable composition segregation, which gradually disappeared with increasing annealing temperature, and the micro-structure changed to an equiaxed structure after annealing the alloy at 1233 K. The electrochemical tests indicated that the annealed alloys demonstrated much better cycling stability compared with the as-cast one. The capacity retention at the 100th cycle increased from 90.0% （as-cast） to 94.7% （1273 K）. The annealing treatment also improved the discharge capacity. However, the high rate dischargeability （HRD） value of the annealed alloy slightly dropped, which was believed to be ascribed to the decreased exchange current density and the hydrogen diffusion coefficient in alloy bulk.展开更多
To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were stud...To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were studied. Nonsubstituted Ml0.80Mg0.20（Ni2.90Co0.50-Mn0.30Al0.30）x （x=0.68, 0.70, 0.72, 0.74, 0.76） alloys and Cu-substituted Ml0.80Mg0.20（Ni2.90Co0.50-yCuyMn0.30Al0.30）0.70 （y=0, 0.10, 0.30, 0.50） alloys were prepared by induction melting. Phase structure analysis shows that the nonsubstituted alloys consist of a LaNi5 phase, a LaNi3 phase, and a minor La2Ni7 phase;in addition, in the case of Cu-substitution, the Nd2Ni7 phase appears and the LaNi3 phase vanishes. Ther-modynamic tests show that the enthalpy change in the dehydriding process decreases, indicating that hydride stability decreases with in-creasing stoichiometry and increasing Cu content. The maximum discharge capacity, kinetic properties, and cycling stability of the alloy electrodes all increase and then decrease with increasing stoichiometry or increasing Cu content. Furthermore, Cu substitution for Co ame-liorates the discharge capacity, kinetics, and cycling stability of the alloy electrodes.展开更多
The effects of the partial replacement of Co with Mo on the phase structure and electrochemical kinetic properties of La0.35Ce0.65Ni3.54Co0.80-xMn0.35Al0.32Mox （x=0.00, 0.10, 0.15, 0.20, 0.25） hydrogen storage alloy...The effects of the partial replacement of Co with Mo on the phase structure and electrochemical kinetic properties of La0.35Ce0.65Ni3.54Co0.80-xMn0.35Al0.32Mox （x=0.00, 0.10, 0.15, 0.20, 0.25） hydrogen storage alloys prepared by arc-melting method were sys-tematically studied in this paper. The X-ray diffraction （XRD） showed that after partial substitution of Mo for Co, the alloys remained a single LaNi5 phase with a hexagonal CaCu5-type structure. The P-C isotherms indicated that the equilibrium pressure gradually decreased with in-creasing of Mo content. Electrochemical studies showed that the substitution of Mo for Co could greatly increase discharge capacity, improve activation ability and reduce self-discharge of alloy electrodes. The alloy with x=0.25 exhibited a higher rate dischargeability （HRD1200= 50.9%）. Moreover, Mo is a vital element in favor of kinetic properties of AB5-type hydrogen storage alloys. As Mo content increased, the ex-change current density I0, the hydrogen diffusion rate gradually increased.展开更多
La（1-x）MgxNi（1.75）Co（2.05）（x=0.07, 0.08, 0.10, 0.13, 0.15） alloys were prepared by high-frequency inductive method, and then their structure and electrochemical properties were investigated systematically. The...La（1-x）MgxNi（1.75）Co（2.05）（x=0.07, 0.08, 0.10, 0.13, 0.15） alloys were prepared by high-frequency inductive method, and then their structure and electrochemical properties were investigated systematically. The XRD analysis revealed that the alloys consisted of LaNi5 phase and La4MgNi（19）（Ce5Co（19） ＋ Pr5Co（19）） phase, and the introduction of Mg could promote the formation of La4MgNi（19） phase. The observation of microstructure showed that all the alloys processed dendritic structure, which was refined with the increase of x value. The electrochemical measurements showed that all the alloys could be activated within 2 cycles, and with increasing x, the maximum discharge capacity obviously increased from 254.00 m Ah/g（x=0.07） to 351.51 mAh/g（x=0.15）, but the cycling stability（S（80）） decreased somehow from 78.4% to 73.9%. Meanwhile, the appropriate addition of Mg could improve the high-rate discharge capacity（HRD） of the alloy electrodes, which was mainly controlled by the electrochemical reaction rate on the surface of the alloys.展开更多
The double hard magnetic phase magnets with nominal compositions of Nd30–xDyxFe69B1（x=2, and 4）（wt.%） were prepared. The magnetic properties of the magnets were measured with a NIM-2000H hysteresigraph. The cryst...The double hard magnetic phase magnets with nominal compositions of Nd30–xDyxFe69B1（x=2, and 4）（wt.%） were prepared. The magnetic properties of the magnets were measured with a NIM-2000H hysteresigraph. The crystalline structures of the magnets were identified by X-ray diffraction（XRD）. The Rietveld refinement was carried out using the FULLPROF software. The scanning electron microscopy（SEM） and transmission electron microscopy（TEM） analyses were carried out in order to investigate the microstructure of the magnets. It showed that the magnets consisted mainly of Nd2Fe14 B phase, and some Nd-rich phase. Two types of matrix-phase grains in dark grey and light grey were found in the magnets with x=2 and 4. The Dy content was obviously different in the two types of grains, which proved that the double hard magnetic phases（Dy-rich and Dy-lean phases） coexisted in the magnet. It revealed that the Nd-rich phases in junction regions had fcc structure, with the unit cell parameter of about 0.52–0.56 nm. The weak superlattice spots were found in the SAD patterns of the junction Nd-rich phases with large scale. The double hard magnetic phase structure seemed to improve the magnetic properties of NdFeB magnets with high coercivity, while decrease the consumption of Dy element, compared with the single alloy magnet.展开更多
In the face of the requirement that nuclear fusion reactor materials exhibit more excellent thermal,mechanical and physical properties,a novel refractory highentropy alloy,WTaHfTiZr was proposed.The constituent elemen...In the face of the requirement that nuclear fusion reactor materials exhibit more excellent thermal,mechanical and physical properties,a novel refractory highentropy alloy,WTaHfTiZr was proposed.The constituent elements were selected in consideration of low activation,high melting point and high thermostability.The alloys were prepared by arc melting.The as-cast alloy shows a dendrite microstructure with two disordered BCC phases,which caused by the preferential nucleation of W and Ta with much higher melting points during solidification.It exhibits a high compressive yield strength of 1,900 MPa and fracture strain of 8.1% at room temperature,and its yield strengths are up to 612 MPa at 700 ℃ and 203 MPa at 1,000 ℃,respectively.The high strengths are attributed mainly to solid solution strengthening and second phase strengthening.This alloy shows great promise as one of the next-generation nuclear fusion reactor materials.展开更多
REMg8.35Ni2.18Al0.21 （RE=La, Ce, Pr, and Nd） alloys were prepared by induction melting and following annealing. X-ray diffraction （XRD） and scanning electron microscopy （SEM） results showed that the alloys were ...REMg8.35Ni2.18Al0.21 （RE=La, Ce, Pr, and Nd） alloys were prepared by induction melting and following annealing. X-ray diffraction （XRD） and scanning electron microscopy （SEM） results showed that the alloys were composed of Mg2Ni, （La, Pr, Nd）MgzNi, （La, Ce）2MgxT, （Ce, Pr, Nd）Mg12 and Ce2Ni7 phases. The above phases were disproportioned into Mg2NiH4, MgH2 and REHx （x=2.5 1 or 3） phases in hydriding. CEH2.51 phase transformed into CEH2.29 phase in dehydriding, whereas LaH3, PrH3 and NdH3 phases re- mained unchanged. The PrMg8.41Ni2.14Al0.20 alloy had the fastest hydriding kinetics and the highest dehydriding plateau pressure while the CeMg8.35Ni2.18Al0.21 alloy presented the best hydriding/dehydriding reversibility. The onset hydrogen desorption tempera- ture of the CeMg8.35Ni2.18Al0.21 hydride decreased remarkably owing to the phase transformation between the Cell2.51 and the CEH2.29.展开更多
New refractory high-entropy alloys,CrHfNbTaTi and CrHfMoTaTi,derived from the well-known HfNbTaTiZr alloy through principal element substitution were prepared using vacuum arc melting.The phase components,microstructu...New refractory high-entropy alloys,CrHfNbTaTi and CrHfMoTaTi,derived from the well-known HfNbTaTiZr alloy through principal element substitution were prepared using vacuum arc melting.The phase components,microstructures,and compressive properties of the alloys in the as-cast state were investigated.Results showed that both alloys were composed of BCC and cubic Laves phases.In terms of mechanical properties,the yield strength increased remarkably from 926 MPa for HfNbTaTiZr to 1258 MPa for CrHfNbTaTi,whereas a promising plastic strain of around 15.0%was retained in CrHfNbTaTi.The morphology and composition of the network-shaped interdendritic regions were closely related to the improved mechanical properties due to elemental substitution.Dendrites were surrounded by an incompact interdendritic shell after Mo incorporation,which deteriorated yield strength and accelerated brittleness.展开更多
Phase structure of sputtered Ta coating in the negative glow space and LPH effect were explored.The whole coating/substrate system is substrate→physically gas-absorbed Fe surface→oxygen-enriched TaOx layer→amorphou...Phase structure of sputtered Ta coating in the negative glow space and LPH effect were explored.The whole coating/substrate system is substrate→physically gas-absorbed Fe surface→oxygen-enriched TaOx layer→amorphous Ta→αandβdual phase→singleαphase.After LPH course,micro structure of Ta coating shows intact,only a few cracks emerge after 100 laser pulses,exhibiting thin HAZ but thick Fe/Ta ICZ,without martensitic transformation.For the electrodeposited Cr coating,continuous thermal stresses produce many extra micro-crack,substrate oxidation and martensitic transformation,leading to crack propagations and final bulk delamination,without any ICZ.展开更多
Phase structure and electrochemical properties of laser sintered La2MgNi9 alloys were studied. The sintered alloys contained a main phase, LaNi5, and a ternary La-Mg-Ni phase, with a PuNi3 structure and a small amount...Phase structure and electrochemical properties of laser sintered La2MgNi9 alloys were studied. The sintered alloys contained a main phase, LaNi5, and a ternary La-Mg-Ni phase, with a PuNi3 structure and a small amount of LaMgNi4. The ternary La-Mg-Ni phase with a PuNi3 structure had the composition of La1.8Mg1.2Ni9 and La2MgNi9, for alloys laser sintered at 1000 and 1400 W, respectively. Owing to further reactions between LaNi5 and LaMgNi4, the amount of the PuNi3 phase increased for alloys sintered at 1400 W. Both alloys had good activation property （three charge/discharge cycles）. The discharge capacities of the sintered alloys were 321.8 and 344.8 mAh/g, respectively. Compared with the alloy laser sintered at 1000 W, the poor cyclic stability of the alloy sintered at 1400 W was mainly attributed to the lower corrosion resistance of the La2MgNi9 phase.展开更多
The Mg-Ni hydrogen storage alloys were prepared using the laser sintering technology. The effects of laser sintering power on the phase component and the weight loss of Mg element for the Mg-Ni alloys were investigate...The Mg-Ni hydrogen storage alloys were prepared using the laser sintering technology. The effects of laser sintering power on the phase component and the weight loss of Mg element for the Mg-Ni alloys were investigated. The samples P1, P2 and P3 consisted of five phases： Mg2Ni, MgNi2, Mg, Ni and MgO. The weight loss of Mg element remarkably increased at 1200 W. The addition of extra Mg significantly promoted the reaction between Mg and Ni. Mg2Ni, MgNi2, and a small amount of Ni and MgO phases were present in the samples PM （pestie milling） and BM （ball milling）. The sample PM has a homogeneous microstructure, and the contents of Mg2Ni and MgNi2 were approximately consistent with those of the Mg-Ni alloy under the equilibrium conditions. The maximum hydrogen storage capacity of the sample BM was 1.72 wt.% and the sample can be activated easily at 573 K （only 3 activation cycles）.展开更多
Taking the hot working die steel （HWDS） 4Cr3Mo2NbVNi as an example, the phase electron structures （PES） and the biphase interface electron structures （BIES） of Mo2C and V4 C3 , which are two kinds of important c...Taking the hot working die steel （HWDS） 4Cr3Mo2NbVNi as an example, the phase electron structures （PES） and the biphase interface electron structures （BIES） of Mo2C and V4 C3 , which are two kinds of important carbides precipitated during tempering in steel were calculated, on the basis of the empirical electron theory of solids and molecules and the improved TFD theory. The influence of Mo2 C and V4 C3 on the mechanical properties of HWDS has been analyzed at electron structure level, and the fundamental reason that the characteristic of the PES and the BIES of carbides decides the behavior of them has been revealed.展开更多
The reconstructed structures of Cu（100） surface induced by O2 dissociative adsorption were investigated by low energy electron diffraction and scanning tunneling microscopy. At lower oxygen coverage, it was found th...The reconstructed structures of Cu（100） surface induced by O2 dissociative adsorption were investigated by low energy electron diffraction and scanning tunneling microscopy. At lower oxygen coverage, it was found that two reconstructed structures, i.e. c（2×2）-O and （√2×2√2）R45°-O are coexistent. The domain size of the c（2×2）-O structure decreased with the increasing of O2 exposure. The reconstructed structure at very small coverage was also investigated and a “zigzag” structure was observed at this stage. The “zigzag” structure was identified as boundaries of local c（2×2） domains. It was found that the strip region shows much stronger molecule-substrate interaction than that of oxygen covered regions, making it a proper template for patterned organic films. The sequence of the thermal stability was found as zigzag structure〉c（2×2）〉（√2×2√2）R45°-O.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.12304089)the start-up foundation from Shanghai University。
文摘LiFePO_(4)has normal olivine-structured(a-LFP)and high pressure(b-LFP)phases,with the former being one of the cathode materials for commercial Li-ion batteries.Despite extensive focus on the respective electrochemical properties of the two phases,there is a lack of comparative studies on their electronic and magnetic properties,and the origin of the structural phase transition remains unclear.By combining first-principles calculations with molecular dynamics simulations,we find that the anisotropic compression of Li-O bonds drives the structural phase transition from a-LFP to b-LFP at a critical pressure of 20 GPa,while b-LFP undergoes a transition from semiconductor to metal due to Fe^(3+)generated during delithiation.Their antiferromagnetic(AFM)ground states are predicted to arise from the negative magnetic exchange interactions between nearest and next-nearest neighbor sites,with the corresponding N'eel temperature showing significant enhancement under pressure.Furthermore,compared with a-LFP,b-LFP shows increases in bulk,shear,and Young’s moduli of 8%,13%,and 12%,respectively.These findings enrich the physical property data of LiFePO_(4)phase compounds,providing knowledge for expanding the application scenarios of the a-LFP phase under special operating conditions such as high pressure.
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.
基金Supported by the National Basic Research Program of China under Grant Nos 2012CV821400 and 2010CB922904the National Science Foundation of China under Grant Nos NSFC-1190024,11175248 and 11104339the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDB07000000
文摘We investigate the electronic structures of FeSe in the presence of different possible orders and spin-orbit coupling （SOC）. It is found that only the ferro-orbital order （FO） and the collinear antiferro-magnetism （C-AFM） can simultaneously induce splittings at F and M. Bicollinear antiferro-magnetism （B-AFM） and SOC have very similar band structures on F-M near the Fermi level. The temperature T insensitive splitting at F and the T-dependent splitting at M observed in recent experiments can be explained by the d-wave bond nematic （dBN） order together with SOC. The recent observed Dirac cones and their T-dependence in FeSe thin films can also be well explained by the dBN order together with the band renormMization. Their thickness- and cobalt-doping- dependent behaviors are the consequences of electron doping and reduction of Se height. All these suggest that the nematic order in the FeSe system is the dBN order.
基金financially supported by the National Natural Science Foundation of China(Grant No.52402215)the Anhui Provincial Natural Science Foundation(2408085QB036)+1 种基金the Natural Science Research Project of Anhui Province Education Department(Grant Nos.2022AH050334,2022AH030046,2023AH051119)the Scientific Research Foundation of Anhui University of Technology for Talent Introduction(DT2200001211)。
文摘Sodium-ion batteries are the prominent device for stationary energy storage system and low-speed electric vehicles.However,the practical application is still limited by the unsatisfied performance and high cost of the cathode side,which strictly requires the development of high voltage,high capacity,and earth-abundant cathode material.Ni-Fe-Mn ternary layered oxide has been recognized as one of the most promising standard type of cathodes.However,the composition and phase structure on high-voltage characteristics have not been well investigated.Herein,selecting the typically high-voltage cathode of P2-Na_(0.67)Ni_(0.33)Mn_(0.67)O_(2)as a parent material,we fabricate ten Ni-Fe-Mn ternary layered oxides through replacing the Ni,Mn,or both Ni and Mn by Fe.The thermodynamically stable phase diagram for those materials is presented.The electrochemical properties for all the samples are investigated in detail.Three potential Ni-Fe-Mn ternary layered oxides are picked up considering the energy density,cycle stability,kinetics,cost price,and working voltage,which demonstrate great potential for surpassing the performance of lithium iron phosphate.The related electrochemical reaction and fading mechanism are well revealed.This work provides some new foundational Ni-Fe-Mn ternary layered materials for high-voltage sodium-ion batteries.
基金National Natural Science Foundation of China (No. 52274403)。
文摘The mechanical,thermodynamic properties and electrical conductivities of L1_(2)-Al_(3)X(X=Zr,Sc,Er,Yb,Hf)structural phases in aluminum conductors were investigated through a first-principles study.The results demonstrate that all structural phases have good alloy-forming ability and structural stability,where Al_(3)Zr is the most superior.Al_(3)Zr,Al_(3)Hf and Al_(3)Sc have enhanced shear and deformation resistance in comparison to other phases.Within the temperature range of 200−600 K,Al_(3)Er and Al_(3)Yb possess the greatest thermodynamic stability,followed by Al_(3)Hf,Al_(3)Zr and Al_(3)Sc.Al_(3)Er and Al_(3)Yb have higher thermodynamic stability than Al_(3)Hf,Al_(3)Zr and Al_(3)Sc.All structural phases exhibit substantial metallic properties,indicating their good electrical conductivity.The electrical conductivities of Al_(3)Hf and Al_(3)Zr are higher than those of Al_(3)Er,Al_(3)Yb and Al_(3)Sc.The covalent bond properties in Al_(3)Sc,Al_(3)Er and Al_(3)Yb enhance the hardness,brittleness and thermodynamic stability of the structural phase.The thermodynamic stability of Al_(3)Sc is significantly reduced by ionic bonds.
基金Project (51001043) supported by the National Natural Science Foundation of ChinaProject (NCET2011) supported by Program for New Century Excellent Talents in University, China+4 种基金Project (201104390) supported by China Postdoctoral Science Special FoundationProject (20100470990) supported by China Postdoctoral Science FoundationProject (2012IRTSTHN007) supported by Program for Innovative Research Team (in Science and Technology) in the University of Henan Province, ChinaProject (2011J1003) supported by Baotou Science and Technology Project, ChinaProject (B2010-13) supported by the Doctoral Foundation of Henan Polytechnic University, China
文摘La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75-xFex （x=0-0.20） hydrogen storage alloys were synthesized by induction melting and subsequent annealing treatment, and phase structure and electrochemical characteristics were investigated. All alloys consist of a single LaNi5 phase with CaCu5 structure, and the lattice constant a and the cell volume （V） of the LaNi5 phase increase with increasing x value. The maximum discharge capacity gradually decreases from 319.0 mA？h/g （x=0） to 291.9 mA？h/g （x=0.20） with the increase in x value. The high-rate dischargeability at the discharge current density of 1200 mA/g decreases monotonically from 53.1% （x=0） to 44.2% （x=0.20）. The cycling stability increases with increasing x from 0 to 0.20, which is mainly ascribed to the improvement of the pulverization resistance.
基金Project(NCET-11-0554) supported by the Program for New Century Excellent Talents in University,ChinaProject(2011BAE22B04) supported by the National Key Technology R&D Program,ChinaProject(51271206) supported by the National Natural Science Foundation of China
文摘The microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr （x=1, 2, 3, 4; normal mass fraction in %） alloys were investigated. In low Zn content, aside from the major second phase of Mg24（Er, Y, Zn）5, there are a few lamellar phases that grow parallel with each other from the grain boundaries to the grain interior. With Zn content increasing, the Mg24（Er, Y, Zn）5 phase decreases, but the Mg12Zn（Y, Er） phase and lamellar phases continuously increase. When Zn content reaches 4% （normal mass fraction）, the Mg12Zn（Y, Er） phase mainly exists as large bulks, and some a-Mg grains are thoroughly penetrated by the lamellar phases. Moreover, the crystallography structures of the Mgl2Zn（Y, Er） and Mg24（Er, Y, Zn）5 phases are confirmed as 18R-type long-period stacking ordered structure and body-centred cubic structure, respectively.
基金supported by the National Natural Science Foundation of China (No. 20673093)the Natural Science Foundation of Hebei Province, China (No. B2007000303)
文摘The effects of annealing treatment on the microstructure and electrochemical properties of low-Co LaNi 3.55 Mn 0.35 Co 0.20 Al 0.20 Cu 0.75 Fe 0.10 hydrogen storage alloys were investigated. X-ray diffraction （XRD） analysis indicated that annealing treatment remarkably reduced the lattice strain and defects, and increased the unit-cell volume. The optical microscope analysis showed that the as-cast alloy had a crass dendrite microstructure with noticeable composition segregation, which gradually disappeared with increasing annealing temperature, and the micro-structure changed to an equiaxed structure after annealing the alloy at 1233 K. The electrochemical tests indicated that the annealed alloys demonstrated much better cycling stability compared with the as-cast one. The capacity retention at the 100th cycle increased from 90.0% （as-cast） to 94.7% （1273 K）. The annealing treatment also improved the discharge capacity. However, the high rate dischargeability （HRD） value of the annealed alloy slightly dropped, which was believed to be ascribed to the decreased exchange current density and the hydrogen diffusion coefficient in alloy bulk.
基金supported by the National Natural Science Foundation of China(Nos.21303157 and 21106123)the Natural Science Foundation of Hebei Province,China(No.B2012203104)+1 种基金the China Postdoctoral Science Foundation Project(2013M541201)the Research Fund for the Doctoral Program of Higher Education of China(20131333120008)
文摘To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were studied. Nonsubstituted Ml0.80Mg0.20（Ni2.90Co0.50-Mn0.30Al0.30）x （x=0.68, 0.70, 0.72, 0.74, 0.76） alloys and Cu-substituted Ml0.80Mg0.20（Ni2.90Co0.50-yCuyMn0.30Al0.30）0.70 （y=0, 0.10, 0.30, 0.50） alloys were prepared by induction melting. Phase structure analysis shows that the nonsubstituted alloys consist of a LaNi5 phase, a LaNi3 phase, and a minor La2Ni7 phase;in addition, in the case of Cu-substitution, the Nd2Ni7 phase appears and the LaNi3 phase vanishes. Ther-modynamic tests show that the enthalpy change in the dehydriding process decreases, indicating that hydride stability decreases with in-creasing stoichiometry and increasing Cu content. The maximum discharge capacity, kinetic properties, and cycling stability of the alloy electrodes all increase and then decrease with increasing stoichiometry or increasing Cu content. Furthermore, Cu substitution for Co ame-liorates the discharge capacity, kinetics, and cycling stability of the alloy electrodes.
基金supported by the National Natural Science Foundation of China (20673093)
文摘The effects of the partial replacement of Co with Mo on the phase structure and electrochemical kinetic properties of La0.35Ce0.65Ni3.54Co0.80-xMn0.35Al0.32Mox （x=0.00, 0.10, 0.15, 0.20, 0.25） hydrogen storage alloys prepared by arc-melting method were sys-tematically studied in this paper. The X-ray diffraction （XRD） showed that after partial substitution of Mo for Co, the alloys remained a single LaNi5 phase with a hexagonal CaCu5-type structure. The P-C isotherms indicated that the equilibrium pressure gradually decreased with in-creasing of Mo content. Electrochemical studies showed that the substitution of Mo for Co could greatly increase discharge capacity, improve activation ability and reduce self-discharge of alloy electrodes. The alloy with x=0.25 exhibited a higher rate dischargeability （HRD1200= 50.9%）. Moreover, Mo is a vital element in favor of kinetic properties of AB5-type hydrogen storage alloys. As Mo content increased, the ex-change current density I0, the hydrogen diffusion rate gradually increased.
基金Project supported by the National Natural Science Foundation of China(50901036)the Graduate Science and Technology Innovation Project of Jiangsu University of Science and Technology(YCX15S-18)Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘La（1-x）MgxNi（1.75）Co（2.05）（x=0.07, 0.08, 0.10, 0.13, 0.15） alloys were prepared by high-frequency inductive method, and then their structure and electrochemical properties were investigated systematically. The XRD analysis revealed that the alloys consisted of LaNi5 phase and La4MgNi（19）（Ce5Co（19） ＋ Pr5Co（19）） phase, and the introduction of Mg could promote the formation of La4MgNi（19） phase. The observation of microstructure showed that all the alloys processed dendritic structure, which was refined with the increase of x value. The electrochemical measurements showed that all the alloys could be activated within 2 cycles, and with increasing x, the maximum discharge capacity obviously increased from 254.00 m Ah/g（x=0.07） to 351.51 mAh/g（x=0.15）, but the cycling stability（S（80）） decreased somehow from 78.4% to 73.9%. Meanwhile, the appropriate addition of Mg could improve the high-rate discharge capacity（HRD） of the alloy electrodes, which was mainly controlled by the electrochemical reaction rate on the surface of the alloys.
基金Project supported by the National Basic Research Program of China(2014CB643701,2010CB934601)the National Science and Technology Support Program of China(2012BAE02B01)+1 种基金the National Natural Science Foundation of China(51331003,51271060,51171049)the National Key Technology R&D Program(2012BAE02B01)
文摘The double hard magnetic phase magnets with nominal compositions of Nd30–xDyxFe69B1（x=2, and 4）（wt.%） were prepared. The magnetic properties of the magnets were measured with a NIM-2000H hysteresigraph. The crystalline structures of the magnets were identified by X-ray diffraction（XRD）. The Rietveld refinement was carried out using the FULLPROF software. The scanning electron microscopy（SEM） and transmission electron microscopy（TEM） analyses were carried out in order to investigate the microstructure of the magnets. It showed that the magnets consisted mainly of Nd2Fe14 B phase, and some Nd-rich phase. Two types of matrix-phase grains in dark grey and light grey were found in the magnets with x=2 and 4. The Dy content was obviously different in the two types of grains, which proved that the double hard magnetic phases（Dy-rich and Dy-lean phases） coexisted in the magnet. It revealed that the Nd-rich phases in junction regions had fcc structure, with the unit cell parameter of about 0.52–0.56 nm. The weak superlattice spots were found in the SAD patterns of the junction Nd-rich phases with large scale. The double hard magnetic phase structure seemed to improve the magnetic properties of NdFeB magnets with high coercivity, while decrease the consumption of Dy element, compared with the single alloy magnet.
基金financially supported by the National Natural Science Foundation of China (Grant Nos.51971099 and 52071088)
文摘In the face of the requirement that nuclear fusion reactor materials exhibit more excellent thermal,mechanical and physical properties,a novel refractory highentropy alloy,WTaHfTiZr was proposed.The constituent elements were selected in consideration of low activation,high melting point and high thermostability.The alloys were prepared by arc melting.The as-cast alloy shows a dendrite microstructure with two disordered BCC phases,which caused by the preferential nucleation of W and Ta with much higher melting points during solidification.It exhibits a high compressive yield strength of 1,900 MPa and fracture strain of 8.1% at room temperature,and its yield strengths are up to 612 MPa at 700 ℃ and 203 MPa at 1,000 ℃,respectively.The high strengths are attributed mainly to solid solution strengthening and second phase strengthening.This alloy shows great promise as one of the next-generation nuclear fusion reactor materials.
基金Foundation item： Project supported by National High-Tech Research and Development Program of China （2007AA05Z 117）, National Natural Science Foundation of China （50971112, 51171165）, China Postdoctoral Science Foundation （20100470990） and Natural Science Founda- tion of Hebei Province （E2010001170）
文摘REMg8.35Ni2.18Al0.21 （RE=La, Ce, Pr, and Nd） alloys were prepared by induction melting and following annealing. X-ray diffraction （XRD） and scanning electron microscopy （SEM） results showed that the alloys were composed of Mg2Ni, （La, Pr, Nd）MgzNi, （La, Ce）2MgxT, （Ce, Pr, Nd）Mg12 and Ce2Ni7 phases. The above phases were disproportioned into Mg2NiH4, MgH2 and REHx （x=2.5 1 or 3） phases in hydriding. CEH2.51 phase transformed into CEH2.29 phase in dehydriding, whereas LaH3, PrH3 and NdH3 phases re- mained unchanged. The PrMg8.41Ni2.14Al0.20 alloy had the fastest hydriding kinetics and the highest dehydriding plateau pressure while the CeMg8.35Ni2.18Al0.21 alloy presented the best hydriding/dehydriding reversibility. The onset hydrogen desorption tempera- ture of the CeMg8.35Ni2.18Al0.21 hydride decreased remarkably owing to the phase transformation between the Cell2.51 and the CEH2.29.
基金supported by the National Natural Science Foundation of China(No.51604173)the Natural Science Foundation of Jiangsu Higher Education Institution of China(No.18KJB430012)。
文摘New refractory high-entropy alloys,CrHfNbTaTi and CrHfMoTaTi,derived from the well-known HfNbTaTiZr alloy through principal element substitution were prepared using vacuum arc melting.The phase components,microstructures,and compressive properties of the alloys in the as-cast state were investigated.Results showed that both alloys were composed of BCC and cubic Laves phases.In terms of mechanical properties,the yield strength increased remarkably from 926 MPa for HfNbTaTiZr to 1258 MPa for CrHfNbTaTi,whereas a promising plastic strain of around 15.0%was retained in CrHfNbTaTi.The morphology and composition of the network-shaped interdendritic regions were closely related to the improved mechanical properties due to elemental substitution.Dendrites were surrounded by an incompact interdendritic shell after Mo incorporation,which deteriorated yield strength and accelerated brittleness.
基金financial support of the project from the National Natural Science Foundation of China(No.51701223)。
文摘Phase structure of sputtered Ta coating in the negative glow space and LPH effect were explored.The whole coating/substrate system is substrate→physically gas-absorbed Fe surface→oxygen-enriched TaOx layer→amorphous Ta→αandβdual phase→singleαphase.After LPH course,micro structure of Ta coating shows intact,only a few cracks emerge after 100 laser pulses,exhibiting thin HAZ but thick Fe/Ta ICZ,without martensitic transformation.For the electrodeposited Cr coating,continuous thermal stresses produce many extra micro-crack,substrate oxidation and martensitic transformation,leading to crack propagations and final bulk delamination,without any ICZ.
基金the Natural Science Foundation of Anhui Province (070414159)the Science Research Foundation for the Candidates of Academic Leaders of Anhui Proince
文摘Phase structure and electrochemical properties of laser sintered La2MgNi9 alloys were studied. The sintered alloys contained a main phase, LaNi5, and a ternary La-Mg-Ni phase, with a PuNi3 structure and a small amount of LaMgNi4. The ternary La-Mg-Ni phase with a PuNi3 structure had the composition of La1.8Mg1.2Ni9 and La2MgNi9, for alloys laser sintered at 1000 and 1400 W, respectively. Owing to further reactions between LaNi5 and LaMgNi4, the amount of the PuNi3 phase increased for alloys sintered at 1400 W. Both alloys had good activation property （three charge/discharge cycles）. The discharge capacities of the sintered alloys were 321.8 and 344.8 mAh/g, respectively. Compared with the alloy laser sintered at 1000 W, the poor cyclic stability of the alloy sintered at 1400 W was mainly attributed to the lower corrosion resistance of the La2MgNi9 phase.
基金the Natural Science Foundation of Anhui Province, China (No. 070414159)
文摘The Mg-Ni hydrogen storage alloys were prepared using the laser sintering technology. The effects of laser sintering power on the phase component and the weight loss of Mg element for the Mg-Ni alloys were investigated. The samples P1, P2 and P3 consisted of five phases： Mg2Ni, MgNi2, Mg, Ni and MgO. The weight loss of Mg element remarkably increased at 1200 W. The addition of extra Mg significantly promoted the reaction between Mg and Ni. Mg2Ni, MgNi2, and a small amount of Ni and MgO phases were present in the samples PM （pestie milling） and BM （ball milling）. The sample PM has a homogeneous microstructure, and the contents of Mg2Ni and MgNi2 were approximately consistent with those of the Mg-Ni alloy under the equilibrium conditions. The maximum hydrogen storage capacity of the sample BM was 1.72 wt.% and the sample can be activated easily at 573 K （only 3 activation cycles）.
基金ItemSponsored by National Natural Science Foundation of China (50271030) Provincial Natural Science Foundation ofLiaoning Province of China (972072)
文摘Taking the hot working die steel （HWDS） 4Cr3Mo2NbVNi as an example, the phase electron structures （PES） and the biphase interface electron structures （BIES） of Mo2C and V4 C3 , which are two kinds of important carbides precipitated during tempering in steel were calculated, on the basis of the empirical electron theory of solids and molecules and the improved TFD theory. The influence of Mo2 C and V4 C3 on the mechanical properties of HWDS has been analyzed at electron structure level, and the fundamental reason that the characteristic of the PES and the BIES of carbides decides the behavior of them has been revealed.
基金ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China （No.60506019）.
文摘The reconstructed structures of Cu（100） surface induced by O2 dissociative adsorption were investigated by low energy electron diffraction and scanning tunneling microscopy. At lower oxygen coverage, it was found that two reconstructed structures, i.e. c（2×2）-O and （√2×2√2）R45°-O are coexistent. The domain size of the c（2×2）-O structure decreased with the increasing of O2 exposure. The reconstructed structure at very small coverage was also investigated and a “zigzag” structure was observed at this stage. The “zigzag” structure was identified as boundaries of local c（2×2） domains. It was found that the strip region shows much stronger molecule-substrate interaction than that of oxygen covered regions, making it a proper template for patterned organic films. The sequence of the thermal stability was found as zigzag structure〉c（2×2）〉（√2×2√2）R45°-O.
