The effect of lanthanum(La) on nitrogen atom diffusion in ε-Fe3N phase produced during nitriding with and without rare earth addition were studied based on the density function theory of first principles and the quan...The effect of lanthanum(La) on nitrogen atom diffusion in ε-Fe3N phase produced during nitriding with and without rare earth addition were studied based on the density function theory of first principles and the quantum mechanics program CASTEP code of Material Studio software.Calculated results show that the presence of La in ε-Fe3N phase can lead to the shrinks of a and b axis and the elongation of c axis of ε-Fe3N crystal cell.The total energy and the stability of the crystal cell with La are lower and higher than that without La,respectively.Diffusion activation energy of nitrogen atom in ε-Fe3N phase with La is 1.01 eV smaller than that in ε-Fe3N phase without La.This is the main reason why rare earth elements diffusing into compound layer produced during nitriding can accelerate the nitriding process or shorten the nitriding duration.展开更多
Planar films of pure and Ti^(4+)-dopedβ-Fe_(2)O_(3)were prepared by a spray pyrolysis method.X-ray diffraction patterns and Raman spectra of the metastableβ-Fe_(2)O_(3)film showed that its thermal stability was sign...Planar films of pure and Ti^(4+)-dopedβ-Fe_(2)O_(3)were prepared by a spray pyrolysis method.X-ray diffraction patterns and Raman spectra of the metastableβ-Fe_(2)O_(3)film showed that its thermal stability was significantly improved because of covalent bonds in the interfaces between the film and substrate,while only weak Van der Waals bonds existed at the interfaces within the particle-assembledβ-Fe_(2)O_(3)film prepared by electrophoretic deposition.The as-prepared planar films were thus able to withstand higher annealing temperature and stronger laser irradiation power in comparison with theβ-Fe_(2)O_(3)particle-assembly.Ti^(4+)doping was used to increase the concentration of carriers in the metastableβ-Fe_(2)O_(3)film.Compared with pureβ-Fe_(2)O_(3)photoanodes,the highest saturated photocurrent for water splitting over the Ti^(4+)-dopedβ-Fe_(2)O_(3)photoanode was increased by a factor of approximately three.Theβ-Fe_(2)O_(3)photoanode exhibited photochemical stability for water splitting for a duration exceeding 100 h,which indicates its important potential application in solar energy conversion.展开更多
The compressibility and pressure-induced phase transition of β-Si3N4 were investigated by using an angle dispersive x-ray diffraction technique in a diamond anvil cell at room temperature. Rietveld refinements of the...The compressibility and pressure-induced phase transition of β-Si3N4 were investigated by using an angle dispersive x-ray diffraction technique in a diamond anvil cell at room temperature. Rietveld refinements of the x-ray powder diffraction data verified that the hexagonal structure（with space group P63/m, Z = 2 formulas per unit cell） β-Si3N4 remained stable under high pressure up to 37 GPa. Upon increasing pressure, β-Si3 N4 transformed to δ-Si3N4 at about 41 GPa. The initial β-Si3N4 was recovered as the pressure was released to ambient pressure, implying that the observed pressureinduced phase transformation was reversible. The pressure–volume data of β-Si3N4 was fitted by the third-order Birch–Murnaghan equation of state, which yielded a bulk modulus K0= 273（2） GPa with its pressure derivative K0= 4（fixed）and K0= 278（2） GPa with K 0= 5. Furthermore, the compressibility of the unit cell axes（a and c-axes） for the β-Si3N4 demonstrated an anisotropic property with increasing pressure.展开更多
We theoretically provide a magnetic phase diagram for the single-layer(SL)CrBr_(3),which could be effectively tuned by both strain engineering and charge doping in SL-CrBr_(3).Through systematical first-principles cal...We theoretically provide a magnetic phase diagram for the single-layer(SL)CrBr_(3),which could be effectively tuned by both strain engineering and charge doping in SL-CrBr_(3).Through systematical first-principles calculations and Heisenberg model Hamiltonian simulations,three different magnetic phases in SL-CrBr_(3),which are off-plane ferromagnetic,in-plane ferromagnetic and in-plane Neél-antiferromagnetic phases,are found in the strain and charge doping regimes we studied.Furthermore,our results show that higher order Heisenberg exchange parameters and anisotropy exchange parameters should be taken into account for accurately illustrating the magnetic phase transition in SL-CrBr_(3).As a result,we find from the SpinW simulation that the Curie temperature is about T_(c)=38.4 K,which is well consistent with the experimental result 34 K[Nano Lett.193138(2019)].The findings here may be confirmed in future experiments,and may be useful for the potential applications of SL-CrBr_(3)in spintronics field.展开更多
SisN4 and SiC phase stability via gas phase reactions among SiO, CO/CO2 and N2 has been calculated based on thermochemical equilibrium. The influences of carbon activity (αC), and the partial pressure of SiO (PSiO), ...SisN4 and SiC phase stability via gas phase reactions among SiO, CO/CO2 and N2 has been calculated based on thermochemical equilibrium. The influences of carbon activity (αC), and the partial pressure of SiO (PSiO), CO (PCO) and N2 (PN2) on the Si3N4-SiC stability have been studied and the related phase diagrams have been constructed. Result shows that the lowering αC and PCO/PSiO ratio and the increasing PN2 greatly elevate the Si3N4-SiC equilibrium temperature. Some previously observed experimental results related to Si3N4 and SiC formation at different temperature from the gas phase reactions have been discussed and some guides for sintering and synthesis Of the Si3N4 materials have been proposed展开更多
Single‐atom catalysts(SACs)have demonstrated excellent performances in chemoselective hydrogenation reactions.However,the employment of precious metals and/or organic solvents compromises their sustainability.Herein,...Single‐atom catalysts(SACs)have demonstrated excellent performances in chemoselective hydrogenation reactions.However,the employment of precious metals and/or organic solvents compromises their sustainability.Herein,we for the first time report the chemoselective hydrogenation of 3‐nitrostyrene over noble‐metal‐free Co‐N‐C SAC in green solvent—compressed CO2.An interesting inverted V‐curve relation is observed between the catalytic activity and CO2 pressure,where the conversion of 3‐nitrostyrene reaches the maximum of 100%at 5.0 MPa CO2(total pressure of 8.1 MPa).Meanwhile,the selectivities to 3‐vinylaniline at all pressures remain high(>99%).Phase behavior studies reveal that,in sharp contrast with the single phase which is formed at total pressure above 10.8 MPa,bi‐phase composed of CO2/H_(2)gas‐rich phase and CO2‐expanded substrate liquid phase forms at total pressure of 8.1 MPa,which dramatically changes the reaction kinetics of the catalytic system.The reaction order with respect to H_(2)pressure decreases from~0.5 to zero at total pressure of 8.1 MPa,suggesting the dissolved CO2 in 3‐nitrostyrene greatly promotes the dissolution of H_(2)in the substrate,which is responsible for the high catalytic activity at the peak of the inverted V‐curve.展开更多
N-(4-hydroxy-3-methoxyphenylmethylene)-p-methoxyaniline(C15H15NO3) was synthesized by the one step solid phase reactions of p-methoxyaniline with vanillin at room temperature without solvent.The reaction was completed...N-(4-hydroxy-3-methoxyphenylmethylene)-p-methoxyaniline(C15H15NO3) was synthesized by the one step solid phase reactions of p-methoxyaniline with vanillin at room temperature without solvent.The reaction was completed in 15 min and the yield was 93%.The product was characterized by elemental analysis,X-ray powder diffraction,IR and 1H NMR.展开更多
By employing sintering additives of Li2CO3 and Y2O3,porous Si3N4 ceramics are prepared after experiencing the processes of sintering and post-vacuum heat treatment at 1680 and 1550°C,respectively.The experimental...By employing sintering additives of Li2CO3 and Y2O3,porous Si3N4 ceramics are prepared after experiencing the processes of sintering and post-vacuum heat treatment at 1680 and 1550°C,respectively.The experimental results demonstrate the completed phase transformation fromαtoβ-Si3N4 in Si3N4 ceramic samples with a amount of 1.60 wt%Li2CO3(0.65 wt%Li2O)and 0.33 wt%Y2O3 additives.The as-synthesized porous Si3N4 ceramics exhibit high flexural strength((126.7±2.7)MPa)and high open porosity of 50.4%at elevated temperature(1200°C).These results are attributed to the significant role of added Li2CO3 as sintering additive,where the volatilization of intergranular glassy phase occurs during sintering process.Therefore,porous Si3N4 ceramics with desired mechanical property prepared by altering the addition of sintering additives demonstrate their great potential as a promising candidate for high temperature applications.展开更多
基金The work is financially supported by the National Natural Science Foundation of China(No 50471019)the PhD Program Foundation of Ministry of Education of China ( No 20060213017)National Defence Key Laboratory Foundation ( No 9140C500404070C5007)
文摘The effect of lanthanum(La) on nitrogen atom diffusion in ε-Fe3N phase produced during nitriding with and without rare earth addition were studied based on the density function theory of first principles and the quantum mechanics program CASTEP code of Material Studio software.Calculated results show that the presence of La in ε-Fe3N phase can lead to the shrinks of a and b axis and the elongation of c axis of ε-Fe3N crystal cell.The total energy and the stability of the crystal cell with La are lower and higher than that without La,respectively.Diffusion activation energy of nitrogen atom in ε-Fe3N phase with La is 1.01 eV smaller than that in ε-Fe3N phase without La.This is the main reason why rare earth elements diffusing into compound layer produced during nitriding can accelerate the nitriding process or shorten the nitriding duration.
文摘Planar films of pure and Ti^(4+)-dopedβ-Fe_(2)O_(3)were prepared by a spray pyrolysis method.X-ray diffraction patterns and Raman spectra of the metastableβ-Fe_(2)O_(3)film showed that its thermal stability was significantly improved because of covalent bonds in the interfaces between the film and substrate,while only weak Van der Waals bonds existed at the interfaces within the particle-assembledβ-Fe_(2)O_(3)film prepared by electrophoretic deposition.The as-prepared planar films were thus able to withstand higher annealing temperature and stronger laser irradiation power in comparison with theβ-Fe_(2)O_(3)particle-assembly.Ti^(4+)doping was used to increase the concentration of carriers in the metastableβ-Fe_(2)O_(3)film.Compared with pureβ-Fe_(2)O_(3)photoanodes,the highest saturated photocurrent for water splitting over the Ti^(4+)-dopedβ-Fe_(2)O_(3)photoanode was increased by a factor of approximately three.Theβ-Fe_(2)O_(3)photoanode exhibited photochemical stability for water splitting for a duration exceeding 100 h,which indicates its important potential application in solar energy conversion.
基金supported by Chinese Academy of Sciences(Grant Nos.KJCX2-SW-N03 and KJCX2-SW-N20)
文摘The compressibility and pressure-induced phase transition of β-Si3N4 were investigated by using an angle dispersive x-ray diffraction technique in a diamond anvil cell at room temperature. Rietveld refinements of the x-ray powder diffraction data verified that the hexagonal structure（with space group P63/m, Z = 2 formulas per unit cell） β-Si3N4 remained stable under high pressure up to 37 GPa. Upon increasing pressure, β-Si3 N4 transformed to δ-Si3N4 at about 41 GPa. The initial β-Si3N4 was recovered as the pressure was released to ambient pressure, implying that the observed pressureinduced phase transformation was reversible. The pressure–volume data of β-Si3N4 was fitted by the third-order Birch–Murnaghan equation of state, which yielded a bulk modulus K0= 273（2） GPa with its pressure derivative K0= 4（fixed）and K0= 278（2） GPa with K 0= 5. Furthermore, the compressibility of the unit cell axes（a and c-axes） for the β-Si3N4 demonstrated an anisotropic property with increasing pressure.
基金Project supported by the National Natural Science Foundation of China(Grant No.11625415)the Innovation Development Foundation of China Academy of Engineering Physics(Grant No.ZYCX1921-02)。
文摘We theoretically provide a magnetic phase diagram for the single-layer(SL)CrBr_(3),which could be effectively tuned by both strain engineering and charge doping in SL-CrBr_(3).Through systematical first-principles calculations and Heisenberg model Hamiltonian simulations,three different magnetic phases in SL-CrBr_(3),which are off-plane ferromagnetic,in-plane ferromagnetic and in-plane Neél-antiferromagnetic phases,are found in the strain and charge doping regimes we studied.Furthermore,our results show that higher order Heisenberg exchange parameters and anisotropy exchange parameters should be taken into account for accurately illustrating the magnetic phase transition in SL-CrBr_(3).As a result,we find from the SpinW simulation that the Curie temperature is about T_(c)=38.4 K,which is well consistent with the experimental result 34 K[Nano Lett.193138(2019)].The findings here may be confirmed in future experiments,and may be useful for the potential applications of SL-CrBr_(3)in spintronics field.
文摘SisN4 and SiC phase stability via gas phase reactions among SiO, CO/CO2 and N2 has been calculated based on thermochemical equilibrium. The influences of carbon activity (αC), and the partial pressure of SiO (PSiO), CO (PCO) and N2 (PN2) on the Si3N4-SiC stability have been studied and the related phase diagrams have been constructed. Result shows that the lowering αC and PCO/PSiO ratio and the increasing PN2 greatly elevate the Si3N4-SiC equilibrium temperature. Some previously observed experimental results related to Si3N4 and SiC formation at different temperature from the gas phase reactions have been discussed and some guides for sintering and synthesis Of the Si3N4 materials have been proposed
文摘Single‐atom catalysts(SACs)have demonstrated excellent performances in chemoselective hydrogenation reactions.However,the employment of precious metals and/or organic solvents compromises their sustainability.Herein,we for the first time report the chemoselective hydrogenation of 3‐nitrostyrene over noble‐metal‐free Co‐N‐C SAC in green solvent—compressed CO2.An interesting inverted V‐curve relation is observed between the catalytic activity and CO2 pressure,where the conversion of 3‐nitrostyrene reaches the maximum of 100%at 5.0 MPa CO2(total pressure of 8.1 MPa).Meanwhile,the selectivities to 3‐vinylaniline at all pressures remain high(>99%).Phase behavior studies reveal that,in sharp contrast with the single phase which is formed at total pressure above 10.8 MPa,bi‐phase composed of CO2/H_(2)gas‐rich phase and CO2‐expanded substrate liquid phase forms at total pressure of 8.1 MPa,which dramatically changes the reaction kinetics of the catalytic system.The reaction order with respect to H_(2)pressure decreases from~0.5 to zero at total pressure of 8.1 MPa,suggesting the dissolved CO2 in 3‐nitrostyrene greatly promotes the dissolution of H_(2)in the substrate,which is responsible for the high catalytic activity at the peak of the inverted V‐curve.
文摘N-(4-hydroxy-3-methoxyphenylmethylene)-p-methoxyaniline(C15H15NO3) was synthesized by the one step solid phase reactions of p-methoxyaniline with vanillin at room temperature without solvent.The reaction was completed in 15 min and the yield was 93%.The product was characterized by elemental analysis,X-ray powder diffraction,IR and 1H NMR.
基金Project(202045007)supported by the Start-up Funds for Outstanding Talents in Central South University,China。
文摘By employing sintering additives of Li2CO3 and Y2O3,porous Si3N4 ceramics are prepared after experiencing the processes of sintering and post-vacuum heat treatment at 1680 and 1550°C,respectively.The experimental results demonstrate the completed phase transformation fromαtoβ-Si3N4 in Si3N4 ceramic samples with a amount of 1.60 wt%Li2CO3(0.65 wt%Li2O)and 0.33 wt%Y2O3 additives.The as-synthesized porous Si3N4 ceramics exhibit high flexural strength((126.7±2.7)MPa)and high open porosity of 50.4%at elevated temperature(1200°C).These results are attributed to the significant role of added Li2CO3 as sintering additive,where the volatilization of intergranular glassy phase occurs during sintering process.Therefore,porous Si3N4 ceramics with desired mechanical property prepared by altering the addition of sintering additives demonstrate their great potential as a promising candidate for high temperature applications.
