Two-dimensional(2D)nanomaterials with bipolar magnetism show great promise in spintronic applications.Manipulating carriers'spin-polarized orientation in bipolar magnetic semiconductor(BMS)requires a gate voltage,...Two-dimensional(2D)nanomaterials with bipolar magnetism show great promise in spintronic applications.Manipulating carriers'spin-polarized orientation in bipolar magnetic semiconductor(BMS)requires a gate voltage,but that is volatile.Recently,a new method has been proposed to solve the problem of volatility by introducing a ferroelectric gate with proper band alignment.In this paper,we predict that the PdX_(2)(X=F,Cl,Br,I)monolayers are 2D ferromagnetic BMS with dynamic stability,thermal stability,and mechanical stability by first-principles calculations.The critical temperatures are higher than the boiling point of liquid nitrogen and the BMS characteristics are robust against external strains and electric fields for PdCl_(2) and PdBr_(2).Then,we manipulate the spin-polarization of PdCl_(2) and PdBr_(2) by introducing a ferroelectric gate to enable magnetic half-metal/semiconductor switching and spin-up/down polarization switching control.Two kinds of spin devices(multiferroic memory and spin filter)have been proposed to realize the spin-polarized directions of electrons.These results demonstrate that PdCl_(2) and PdBr_(2) with BMS characters can be widely used as a general material structure for spintronic devices.展开更多
LiMn 2O 4-x F x prepared by the sol gel method has a perfect crystal formation .The crystal particle size of the material was medium and distributed uniformly. The substitution of F for O increased the specific...LiMn 2O 4-x F x prepared by the sol gel method has a perfect crystal formation .The crystal particle size of the material was medium and distributed uniformly. The substitution of F for O increased the specific capacity of the material at the cost of the cycleability .The explanation of this results is that the F decreases the valence of Mn,that is,more Mn 3+ and less Mn 4+ exist in the material.The increase of Mn 3+ will improve the initial specific capacity and Mn 3+ is the original reason for Jahn Teller effect that caused the poor cycleability of the cathode material by the micro distortion of the crystal structure. In addition, the expanded measurement of the crystal lattice is also the reason for the poor cycleability.Therefore,the results of F substitution and cation substitution are opposite.If the two methods are combined,they can compensate the inability each other and the satisfactory results may be obtained.展开更多
C_(f)/Ta_(x)Hf_(1−x)C–SiC composites are ideal thermal structural materials for service under extreme conditions of hypersonic vehicles.However,how to synthesize TaxHf1-xC powders and efficiently fabricate C_(f)/Ta_(...C_(f)/Ta_(x)Hf_(1−x)C–SiC composites are ideal thermal structural materials for service under extreme conditions of hypersonic vehicles.However,how to synthesize TaxHf1-xC powders and efficiently fabricate C_(f)/Ta_(x)Hf_(1−x)C–SiC composites still faces some challenges.Furthermore,mechanical properties and thermophysical properties of Ta_(x)Hf_(1−x)C vary with the composition,but not monotonically.In-depth analysis of mechanical behaviors of the C_(f)/Ta_(x)Hf_(1−x)C–SiC composites is extremely important for their development and applications.In this study,the Ta_(x)Hf_(1−x)C powders(x=0.2,0.5,0.8)were successfully synthesized via solid solution of TaC and HfC at a relatively low temperature of 1800℃,with a small amount of Si as an additive.Subsequently,the efficient fabrication of 2D-C_(f)/Ta_(x)Hf_(1−x)C–SiC composites was achieved by slurry impregnation and lamination(SIL)combined with precursor infiltration and pyrolysis(PIP).In addition,the mechanical behavior of the composites was investigated systematically.It is demonstrated that the composites present remarkable non-brittle fractures,including a large number of fiber pull out and interphase debonding.Also,the fracture failure involves a complex process of microcrack generation and propagation,matrix cracking,and layer fracture.Moreover,the interfacial bonding between the fibers and the matrix is enhanced as the Ta∶Hf ratio decreases from 4∶1 to 1∶4.As a result,C_(f)/Ta_(0.2)Hf_(0.8)C–SiC composites exhibit exceptional flexural strength of 437±19 MPa,improved by 46%compared with C_(f)/Ta_(0.8)Hf_(0.2)C–SiC(299±19 MPa).This study provides a new perception of design and fabrication of ultra-high-temperature ceramic(UHTC)matrix composites with high performance.展开更多
The proton-transfer between ammonia/water and HF/HBr without and with the stimulus of external electric fields（Eext） was investigated with the ab initio calculations. When external electric field is applied, the pro...The proton-transfer between ammonia/water and HF/HBr without and with the stimulus of external electric fields（Eext） was investigated with the ab initio calculations. When external electric field is applied, the proton transfer occurs, resulting in ion-paired HaN＋X- and H30＋X-（X--Br and F） from hydrogen-bonded complexes in view of the great changes of geometrical structures, dipole moments, frontier molecular orbitals and potential energy surfaces in the critical external electric fields（Ec） of 1.131 × 107 V/cm for H3N-HBr, 1.378× 108 V/cm for H3N-HF, 9.358×107 V/cm for H2O-HBr and 2.304×108 V/cm for H2O-HF, respectively. Furthermore, one or three excess electrons can trigger the proton transfer from H3N-HBr and H3N-HF to HaN＋Br- and H4N＋F-, while two and four excess electrons can induce the proton transfer from H2O-HBr and H2O-HF to H3O＋Br- and H30＋F-, respectively. Compared with that of the analogous NH3/H2O-HC1 systems, the strength of Ec of proton transfer increases from HBr to HCL and HF for either H3N-HX or H2O-HX series, which is understandable by the fact that the acidity sequence is HBr〉HCI〉HF. And the larger of acidity of conjugated acid, the smaller of needed Ec. On the other hand, the Ec for the systems of NH3 with a stronger basicity is generally smaller than that of H2O systems for the same con- jugated acid.展开更多
基金Project supported by the Taishan Scholar Program of Shandong Province,China (Grant No.ts20190939)the Independent Cultivation Program of Innovation Team of Jinan City (Grant No.2021GXRC043)+1 种基金the National Natural Science Foundation of China (Grant No.52173283)the Natural Science Foundation of Shandong Province (Grant No.ZR2020QA052)。
文摘Two-dimensional(2D)nanomaterials with bipolar magnetism show great promise in spintronic applications.Manipulating carriers'spin-polarized orientation in bipolar magnetic semiconductor(BMS)requires a gate voltage,but that is volatile.Recently,a new method has been proposed to solve the problem of volatility by introducing a ferroelectric gate with proper band alignment.In this paper,we predict that the PdX_(2)(X=F,Cl,Br,I)monolayers are 2D ferromagnetic BMS with dynamic stability,thermal stability,and mechanical stability by first-principles calculations.The critical temperatures are higher than the boiling point of liquid nitrogen and the BMS characteristics are robust against external strains and electric fields for PdCl_(2) and PdBr_(2).Then,we manipulate the spin-polarization of PdCl_(2) and PdBr_(2) by introducing a ferroelectric gate to enable magnetic half-metal/semiconductor switching and spin-up/down polarization switching control.Two kinds of spin devices(multiferroic memory and spin filter)have been proposed to realize the spin-polarized directions of electrons.These results demonstrate that PdCl_(2) and PdBr_(2) with BMS characters can be widely used as a general material structure for spintronic devices.
文摘LiMn 2O 4-x F x prepared by the sol gel method has a perfect crystal formation .The crystal particle size of the material was medium and distributed uniformly. The substitution of F for O increased the specific capacity of the material at the cost of the cycleability .The explanation of this results is that the F decreases the valence of Mn,that is,more Mn 3+ and less Mn 4+ exist in the material.The increase of Mn 3+ will improve the initial specific capacity and Mn 3+ is the original reason for Jahn Teller effect that caused the poor cycleability of the cathode material by the micro distortion of the crystal structure. In addition, the expanded measurement of the crystal lattice is also the reason for the poor cycleability.Therefore,the results of F substitution and cation substitution are opposite.If the two methods are combined,they can compensate the inability each other and the satisfactory results may be obtained.
基金support from the National Key R&D Program of China(No.2022YFB3707700)Program of Shanghai Academic/Technology Research Leader(No.23XD1424300)the National Natural Science Foundation of China(No.52332003)are greatly acknowledged.
文摘C_(f)/Ta_(x)Hf_(1−x)C–SiC composites are ideal thermal structural materials for service under extreme conditions of hypersonic vehicles.However,how to synthesize TaxHf1-xC powders and efficiently fabricate C_(f)/Ta_(x)Hf_(1−x)C–SiC composites still faces some challenges.Furthermore,mechanical properties and thermophysical properties of Ta_(x)Hf_(1−x)C vary with the composition,but not monotonically.In-depth analysis of mechanical behaviors of the C_(f)/Ta_(x)Hf_(1−x)C–SiC composites is extremely important for their development and applications.In this study,the Ta_(x)Hf_(1−x)C powders(x=0.2,0.5,0.8)were successfully synthesized via solid solution of TaC and HfC at a relatively low temperature of 1800℃,with a small amount of Si as an additive.Subsequently,the efficient fabrication of 2D-C_(f)/Ta_(x)Hf_(1−x)C–SiC composites was achieved by slurry impregnation and lamination(SIL)combined with precursor infiltration and pyrolysis(PIP).In addition,the mechanical behavior of the composites was investigated systematically.It is demonstrated that the composites present remarkable non-brittle fractures,including a large number of fiber pull out and interphase debonding.Also,the fracture failure involves a complex process of microcrack generation and propagation,matrix cracking,and layer fracture.Moreover,the interfacial bonding between the fibers and the matrix is enhanced as the Ta∶Hf ratio decreases from 4∶1 to 1∶4.As a result,C_(f)/Ta_(0.2)Hf_(0.8)C–SiC composites exhibit exceptional flexural strength of 437±19 MPa,improved by 46%compared with C_(f)/Ta_(0.8)Hf_(0.2)C–SiC(299±19 MPa).This study provides a new perception of design and fabrication of ultra-high-temperature ceramic(UHTC)matrix composites with high performance.
基金the Natural Science Foundation of Guangdong Province of China（No.S2013010014476） and the Engagement Fund of Shantou University, China（No.NFC 13001）.
文摘The proton-transfer between ammonia/water and HF/HBr without and with the stimulus of external electric fields（Eext） was investigated with the ab initio calculations. When external electric field is applied, the proton transfer occurs, resulting in ion-paired HaN＋X- and H30＋X-（X--Br and F） from hydrogen-bonded complexes in view of the great changes of geometrical structures, dipole moments, frontier molecular orbitals and potential energy surfaces in the critical external electric fields（Ec） of 1.131 × 107 V/cm for H3N-HBr, 1.378× 108 V/cm for H3N-HF, 9.358×107 V/cm for H2O-HBr and 2.304×108 V/cm for H2O-HF, respectively. Furthermore, one or three excess electrons can trigger the proton transfer from H3N-HBr and H3N-HF to HaN＋Br- and H4N＋F-, while two and four excess electrons can induce the proton transfer from H2O-HBr and H2O-HF to H3O＋Br- and H30＋F-, respectively. Compared with that of the analogous NH3/H2O-HC1 systems, the strength of Ec of proton transfer increases from HBr to HCL and HF for either H3N-HX or H2O-HX series, which is understandable by the fact that the acidity sequence is HBr〉HCI〉HF. And the larger of acidity of conjugated acid, the smaller of needed Ec. On the other hand, the Ec for the systems of NH3 with a stronger basicity is generally smaller than that of H2O systems for the same con- jugated acid.
