The electronic structure and ionic dynamic properties of pure and Na doped （Li site） LiFePO4 have been investigated by first-principles calculations. The band gap of the Na doped material is much narrow than that of...The electronic structure and ionic dynamic properties of pure and Na doped （Li site） LiFePO4 have been investigated by first-principles calculations. The band gap of the Na doped material is much narrow than that of the undoped one, indicating of better electronic conductive properties. First-principles based molecular dynamic simulations have been performed to examine the migration energy barriers for the Li ion diffusion. The results shown that the energy barriers for Li diffusion decreased a little along the one-dimensional diffusion pathway, indicating that the ionic conductive property is also improved, as compared with the high valance doping （such as CF） cases.展开更多
By employing the first-principles pseudopotential plane-wave method, the physical properties of zincblende ZnO are investigated in comparison with those of the common wurtzite structure. Zincblende ZnO is predicted to...By employing the first-principles pseudopotential plane-wave method, the physical properties of zincblende ZnO are investigated in comparison with those of the common wurtzite structure. Zincblende ZnO is predicted to be a direct gap semiconductor. Compared to the wurtzite structure, the zincblende ZnO is characterized by smaller bandgap and pressure coefficient, larger electron effective mass, increasing static dielectric constants and more covalent bonding. Furthermore, the optical properties including dielectric function and energy loss function of zincblende ZnO were obtained and analysed with some features. These aspects reveal promising applications of zincblende ZnO in optoelectronic devices.展开更多
We report a new diamond synthesis process in which cubic boron nitride single crystals are used as seeds, FesoNi20 alloy powder is used as catalyst/solvent and natural flake-like graphite is used as the carbon source....We report a new diamond synthesis process in which cubic boron nitride single crystals are used as seeds, FesoNi20 alloy powder is used as catalyst/solvent and natural flake-like graphite is used as the carbon source. The samples are investigated using laser Raman spectra and x-ray diffraction （XRD）. Morphology of the sample is observed by a scanning electron microscope （SEM）. Based on the measurement results, we conclude that diamond single crystals have grown on the cBN crystal seeds under the conditions of high temperature 1230℃ and high pressure 4.8 GPa. This work provides an original method for synthesis of high quality hereto-semiconductor with cBN and diamond single crystals, and paves the way for future development.展开更多
The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation （GGA） as well as the on-sit...The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation （GGA） as well as the on-site Coulomb interaction correction （＋U）. The Seebeck coefficient of TiS2 is calculated based on the electronic structure obtained within the GGA under the consideration of the on-site Coulomb interaction. The calculated Seebeck coefficient at 300K shows that Coulomb interaction U in the range of 4.97-5.42eV is important to reproduce the experimental data. The obtained energy gap Eg around 0.05 eV indicates that TiS2 is an indirect narrow-gap semiconductor.展开更多
A first-principles plane wave method with the ultrasoft pseudopotential scheme in the frame of the density functional theory （DFT） is performed to calculate the lattice parameters a and c, the bulk modulus B0 and it...A first-principles plane wave method with the ultrasoft pseudopotential scheme in the frame of the density functional theory （DFT） is performed to calculate the lattice parameters a and c, the bulk modulus B0 and its pressure derivative B0 of the zinc-blende GaAs （ZB-GaAs）, rocksalt GaAs （RS-GaAs）, CsCl-GaAs, NiAs- GaAs and wurtzite GaAs （WZ-GaAs）. Our results are consistent with the available experimental data and other theoretical results. We also calculate the phase transition pressures among these different phases. The results are satisfactory.展开更多
Hybrid density functional theory （DFT） calculations are performed to study MC2 （M= V, Cr, Fe and Co） clusters in the neutral and anionic charge states. We find that the equilibrium geometries of MC2 and their anio...Hybrid density functional theory （DFT） calculations are performed to study MC2 （M= V, Cr, Fe and Co） clusters in the neutral and anionic charge states. We find that the equilibrium geometries of MC2 and their anions are all cyclic structures with C2v symmetry, which agrees well with the previous theoretical studies. The Mulliken charge and spin populations of MC2 clusters and their anions are also calculated, and it is found that the electron charge transformations from anions to neutral molecules mainly take place on the M atoms. Time-dependent DFT is used to calculate the excited states, and a theoretical assignment for the features in the experimental photoelectron spectrum is given, which are in good agreement with the available experimental data.展开更多
Zn0.99Co0.01O nano-needles are synthesized by using pure ZnO powder as the starting material via chemical reactions in ammonia aqueous solution. The nano-needles show the room-temperature ferromagnetism （RTFM） chara...Zn0.99Co0.01O nano-needles are synthesized by using pure ZnO powder as the starting material via chemical reactions in ammonia aqueous solution. The nano-needles show the room-temperature ferromagnetism （RTFM） characterized by using a superconducting quantum interference device. Non-reductive chemical synthesis steps ensure to prevent forming Co-metal nanoclusters within the doped sample. All the results of thermal gravimetric analysis, Fourier transform infrared spectroscopy, x-ray diffraction and ultraviolet spectroscopy demonstrate that Co ions have doped into ZnO lattices and occupied some Zn sites without changing the wurtzite structure of ZnO lattices, and no potential second phase except for the doped Co ions substituting the Zn sites in ZnO lattice can account for the observed RTFM behaviour. Moreover, the synthesis process is of high reproducibility over 80% which is higher than that of commonly-used sol-gel method.展开更多
The photoluminescence spectrum （PL） of InAs quantum dots （QDs） at 80 K is studied by comparison between the theoretical calculation and experimental measurement. The Gaussian line shape is used to approximate the ...The photoluminescence spectrum （PL） of InAs quantum dots （QDs） at 80 K is studied by comparison between the theoretical calculation and experimental measurement. The Gaussian line shape is used to approximate the size distribution of QDs. Its mean volume and the standard full width at half maximum （FWHM） of the PL spectrum. size deviation are well correlated with the peak and The experimental PL spectrum is well reproduced by the theoretical model based on the effect mass approximation including the size distribution without any adjustable parameters. Compared with the standard size deviation value σ = 9 × 10^-2 determined by atomic force microscopic method a small value σ = 7 × 10^-2 is obtained by the best fitting process from the measured and calculated PL spectra.展开更多
A chemical reaction for the preparation of B-C-N compounds by using carbon tetrachloride （CC14）, boron tribromide （BBr3）, lithium nitride （Li3N） and sodium as reactants has been carried out at the temperature of...A chemical reaction for the preparation of B-C-N compounds by using carbon tetrachloride （CC14）, boron tribromide （BBr3）, lithium nitride （Li3N） and sodium as reactants has been carried out at the temperature of 400℃. Measurements of FTIR, XRD, TEM and EELS show that two kinds of compounds have been formed in the prepared sample. One is hollow sphere-like C-N with an amorphous, structure; the other is piece-like polycrystalline B-C-N with the hexagonal structure. Their determined compositions are close to C3N and BC2N, respectively.展开更多
We investigate the properties of light emission from amorphous-Si：H/SiO2 and nc-Si/SiO2 multilayers （MLs）. The size dependence of light emission is well exhibited when the a-Si：H sublayer thickness is thinner than...We investigate the properties of light emission from amorphous-Si：H/SiO2 and nc-Si/SiO2 multilayers （MLs）. The size dependence of light emission is well exhibited when the a-Si：H sublayer thickness is thinner than 4 nm and the interface states are well passlvated by hydrogen. For the nc-Si/Si02 MLs, the oxygen modified interface states and nanocrystalline silicon play a predominant role in the properties of light emission. It is found that the light emission from nc-Si/SiO2 is in agreement with the model of interface state combining with quantum confinement when the size of nc-Si is smaller than 4 nm. The role of hydrogen and oxygen is discussed in detail.展开更多
The equilibrium lattice constants, bulk modulus, shear modulus, elastic constants and Debye temperature of LaNi4.75 Sn0.25 under pressure are calculated using the full-potential linearized augmented plane wave （FP-L...The equilibrium lattice constants, bulk modulus, shear modulus, elastic constants and Debye temperature of LaNi4.75 Sn0.25 under pressure are calculated using the full-potential linearized augmented plane wave （FP-LAPW） method as well as the quasi-harmonic Debye model. The results at zero pressure are in excellent agreement with the experimental data. The Sn atom is found to occupy the equivalent 3g site （0.5a, 0.75b, 0.5c） in the quadruple cell. The Debye temperature of LaNi4.75Sn0.25 is lower than that of LaNi5. The dependences of bulk modulus on finite temperature and on finite pressure are also investigated. The results show that the bulk modulus B increases monotonously as pressure increases.展开更多
The study of electrical resistivity of simple binary liquid alloy Na-K is presented as a function of concentration. Hard sphere diameters of sodium （Na） and potassium （K） are obtained through the inter ionic pair ...The study of electrical resistivity of simple binary liquid alloy Na-K is presented as a function of concentration. Hard sphere diameters of sodium （Na） and potassium （K） are obtained through the inter ionic pair potentials evaluated using Troullier and Martins ab-initio pseudopotentials, which have been used to calculate partial structure factors S（q）. Tile Ziman formula for calculating resistivity of binary liquid alloys has been used. Form factors are calculated using ab-initio pseudopotentials. Tile results suggest that the first principle approach for calculating pseudopotentials with in the frame work of Ziman formalism is quite successful in explaining the electrical resistivity data of compound forming binary liquid alloys.展开更多
Polarizabilities of small Sn （n = 2-8） clusters are calculated by using the higher-order finite-difference pseudopotential density functional method in real space. We find that the polarizabilities of the clusters a...Polarizabilities of small Sn （n = 2-8） clusters are calculated by using the higher-order finite-difference pseudopotential density functional method in real space. We find that the polarizabilities of the clusters are considered to be higher than the value estimated from the “hard sphere” model using the bulk static dielectric constant. The computed polarizabilities per atom tend to decrease with the increasing cluster size. The polarizabilities are closely related to the HOMO-LUMO gaps and the geometrical configurations.展开更多
The ground state properties and equation of state of the non-oxide perovstdte-type superconductor MgCNi3 are investigated by first-principles calculations based on the plane-wave basis set with the local density appro...The ground state properties and equation of state of the non-oxide perovstdte-type superconductor MgCNi3 are investigated by first-principles calculations based on the plane-wave basis set with the local density approximation （LDA） as well as the generalized gradient approximation （GGA） for exchange and correlation, which agree well with both theoretical calculations and experiments. Some thermodynamic properties including the heat capacity, the thermal expansion coefficient and the Griineisen parameter for perovskite structure MgCNi3 are obtained. The dependences of these thermodynamic properties on pressure and temperature are given for the first time.展开更多
Hydrogen energy carrier produced by water electrolysis in alkaline electrolytes is rather meaningful and significant for global sustainability imperatives,while the highpH condition usually leads to a poor reversibili...Hydrogen energy carrier produced by water electrolysis in alkaline electrolytes is rather meaningful and significant for global sustainability imperatives,while the highpH condition usually leads to a poor reversibility of proton adsorption and desorption that significantly determines the hydrogen-generation activity in hydrogen evolution reaction(HER)process.Herein,we demonstrate a remarkable Ru-Mo solid-solution nanocrystal catalyst in alkaline HER process by a very simple but feasible pyrolysis and alkali leaching strategy.Benefiting from the pinning effect and local chemical-and electronic-structure regulations of Mo solute atoms,an ultra-low overpotential(17.3 mV)and an exceptional stability(>100 h)at the typical current density of 10 mA·cm^(−2)are achieved on the ultrasmall Ru-Mo solid-solution nanocrystal catalyst in 1.0 M KOH electrolyte.Density function theory(DFT)calculations gain an insight into the synergistic effect of neighboring Ru and Mo sites in alkaline HER process,where Mo solute atoms are beneficial for the adsorption and activation of water molecules for proton generation and accumulation due to their rich outermost 4d vacant orbitals,while the energy-favorable Ru sites are responsible for the fast deprotonation kinetics of hydrogen intermediates.Our work may provide an interesting route for the development of efficient and stable solid-solution alloy nanocrystals towards alkaline water electrolysis and beyond.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 10564002, the National Key Basic Research and Development Programme of China under Grant No 2002CB211802, and the 0pen Project of Key Laboratory for 0ptoelectronics of Jiangxi Province under Grant No 2004003.
文摘The electronic structure and ionic dynamic properties of pure and Na doped （Li site） LiFePO4 have been investigated by first-principles calculations. The band gap of the Na doped material is much narrow than that of the undoped one, indicating of better electronic conductive properties. First-principles based molecular dynamic simulations have been performed to examine the migration energy barriers for the Li ion diffusion. The results shown that the energy barriers for Li diffusion decreased a little along the one-dimensional diffusion pathway, indicating that the ionic conductive property is also improved, as compared with the high valance doping （such as CF） cases.
基金Supported by the National Natural Science Foundation of China under Grant No 50325103, and the National Basic Research Programme of China under Grant No 2005Ct3724404.
文摘By employing the first-principles pseudopotential plane-wave method, the physical properties of zincblende ZnO are investigated in comparison with those of the common wurtzite structure. Zincblende ZnO is predicted to be a direct gap semiconductor. Compared to the wurtzite structure, the zincblende ZnO is characterized by smaller bandgap and pressure coefficient, larger electron effective mass, increasing static dielectric constants and more covalent bonding. Furthermore, the optical properties including dielectric function and energy loss function of zincblende ZnO were obtained and analysed with some features. These aspects reveal promising applications of zincblende ZnO in optoelectronic devices.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50572032 and 50731006.
文摘We report a new diamond synthesis process in which cubic boron nitride single crystals are used as seeds, FesoNi20 alloy powder is used as catalyst/solvent and natural flake-like graphite is used as the carbon source. The samples are investigated using laser Raman spectra and x-ray diffraction （XRD）. Morphology of the sample is observed by a scanning electron microscope （SEM）. Based on the measurement results, we conclude that diamond single crystals have grown on the cBN crystal seeds under the conditions of high temperature 1230℃ and high pressure 4.8 GPa. This work provides an original method for synthesis of high quality hereto-semiconductor with cBN and diamond single crystals, and paves the way for future development.
基金Supported by the National Science Foundation of China under Grant Nos 10504036 and 50472097, the Special Funds for Major State Basic Research Project of China under Grant No 2005CB623603, the Knowledge Innovation Programme of Chinese Academy of Sciences, and Director Grants of Hefei Institutes of Physical Sciences.
文摘The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation （GGA） as well as the on-site Coulomb interaction correction （＋U）. The Seebeck coefficient of TiS2 is calculated based on the electronic structure obtained within the GGA under the consideration of the on-site Coulomb interaction. The calculated Seebeck coefficient at 300K shows that Coulomb interaction U in the range of 4.97-5.42eV is important to reproduce the experimental data. The obtained energy gap Eg around 0.05 eV indicates that TiS2 is an indirect narrow-gap semiconductor.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10776022, 10576020, and 60436010.
文摘A first-principles plane wave method with the ultrasoft pseudopotential scheme in the frame of the density functional theory （DFT） is performed to calculate the lattice parameters a and c, the bulk modulus B0 and its pressure derivative B0 of the zinc-blende GaAs （ZB-GaAs）, rocksalt GaAs （RS-GaAs）, CsCl-GaAs, NiAs- GaAs and wurtzite GaAs （WZ-GaAs）. Our results are consistent with the available experimental data and other theoretical results. We also calculate the phase transition pressures among these different phases. The results are satisfactory.
基金Supported by the National Natural Science Foundation of China under Grant No 10174039, the Natural Science Foundation of Jiangsu Province under Grant No BK2002099, and the Science Foundation of Nanjing University of Science and Technology under Grant No AB96129.
文摘Hybrid density functional theory （DFT） calculations are performed to study MC2 （M= V, Cr, Fe and Co） clusters in the neutral and anionic charge states. We find that the equilibrium geometries of MC2 and their anions are all cyclic structures with C2v symmetry, which agrees well with the previous theoretical studies. The Mulliken charge and spin populations of MC2 clusters and their anions are also calculated, and it is found that the electron charge transformations from anions to neutral molecules mainly take place on the M atoms. Time-dependent DFT is used to calculate the excited states, and a theoretical assignment for the features in the experimental photoelectron spectrum is given, which are in good agreement with the available experimental data.
基金Supported by the National Natural Science Foundation of China under Grant No 20401001, the Key Project of Anhui Provincial Science and Technology Department under Grant No 04022075, the Project of Anhui Provincial Educational Department under Grant No 2004jq113, and the Fund of Laboratory of Solid State Microstructures, Nanjing University under Grant No M031803.
文摘Zn0.99Co0.01O nano-needles are synthesized by using pure ZnO powder as the starting material via chemical reactions in ammonia aqueous solution. The nano-needles show the room-temperature ferromagnetism （RTFM） characterized by using a superconducting quantum interference device. Non-reductive chemical synthesis steps ensure to prevent forming Co-metal nanoclusters within the doped sample. All the results of thermal gravimetric analysis, Fourier transform infrared spectroscopy, x-ray diffraction and ultraviolet spectroscopy demonstrate that Co ions have doped into ZnO lattices and occupied some Zn sites without changing the wurtzite structure of ZnO lattices, and no potential second phase except for the doped Co ions substituting the Zn sites in ZnO lattice can account for the observed RTFM behaviour. Moreover, the synthesis process is of high reproducibility over 80% which is higher than that of commonly-used sol-gel method.
基金Supported by the National Natural Science Foundation of China under Grant No 10474020, the National Basic Research Programme of China under Grant No 2006CB13921507, and the Knowledge Innovation Project of Chinese Academy of Sciences.
文摘The photoluminescence spectrum （PL） of InAs quantum dots （QDs） at 80 K is studied by comparison between the theoretical calculation and experimental measurement. The Gaussian line shape is used to approximate the size distribution of QDs. Its mean volume and the standard full width at half maximum （FWHM） of the PL spectrum. size deviation are well correlated with the peak and The experimental PL spectrum is well reproduced by the theoretical model based on the effect mass approximation including the size distribution without any adjustable parameters. Compared with the standard size deviation value σ = 9 × 10^-2 determined by atomic force microscopic method a small value σ = 7 × 10^-2 is obtained by the best fitting process from the measured and calculated PL spectra.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50225207, 10325417, 50372055, 50472051 and 50532020, and the National Basic Research Programme of China under Grant No 2005CB724400.
文摘A chemical reaction for the preparation of B-C-N compounds by using carbon tetrachloride （CC14）, boron tribromide （BBr3）, lithium nitride （Li3N） and sodium as reactants has been carried out at the temperature of 400℃. Measurements of FTIR, XRD, TEM and EELS show that two kinds of compounds have been formed in the prepared sample. One is hollow sphere-like C-N with an amorphous, structure; the other is piece-like polycrystalline B-C-N with the hexagonal structure. Their determined compositions are close to C3N and BC2N, respectively.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60508009, 90301009, 60471021, 50472066, and 10574069, and the State Key Basic Research Programme of China under Grant No 2006CB932202.
文摘We investigate the properties of light emission from amorphous-Si：H/SiO2 and nc-Si/SiO2 multilayers （MLs）. The size dependence of light emission is well exhibited when the a-Si：H sublayer thickness is thinner than 4 nm and the interface states are well passlvated by hydrogen. For the nc-Si/Si02 MLs, the oxygen modified interface states and nanocrystalline silicon play a predominant role in the properties of light emission. It is found that the light emission from nc-Si/SiO2 is in agreement with the model of interface state combining with quantum confinement when the size of nc-Si is smaller than 4 nm. The role of hydrogen and oxygen is discussed in detail.
基金Supported by the National Natural Science Foundation of China under Grant No 60777012, and the Programme for Science and Technology Innovation Talents in Universities of Henan Province under Grant No 2008HASTIT008.
文摘The equilibrium lattice constants, bulk modulus, shear modulus, elastic constants and Debye temperature of LaNi4.75 Sn0.25 under pressure are calculated using the full-potential linearized augmented plane wave （FP-LAPW） method as well as the quasi-harmonic Debye model. The results at zero pressure are in excellent agreement with the experimental data. The Sn atom is found to occupy the equivalent 3g site （0.5a, 0.75b, 0.5c） in the quadruple cell. The Debye temperature of LaNi4.75Sn0.25 is lower than that of LaNi5. The dependences of bulk modulus on finite temperature and on finite pressure are also investigated. The results show that the bulk modulus B increases monotonously as pressure increases.
文摘The study of electrical resistivity of simple binary liquid alloy Na-K is presented as a function of concentration. Hard sphere diameters of sodium （Na） and potassium （K） are obtained through the inter ionic pair potentials evaluated using Troullier and Martins ab-initio pseudopotentials, which have been used to calculate partial structure factors S（q）. Tile Ziman formula for calculating resistivity of binary liquid alloys has been used. Form factors are calculated using ab-initio pseudopotentials. Tile results suggest that the first principle approach for calculating pseudopotentials with in the frame work of Ziman formalism is quite successful in explaining the electrical resistivity data of compound forming binary liquid alloys.
基金Supported by the National Natural Science Foundation of China under Grant No 10274055, the Scientific Research Foundation for the Returned 0verseas Chinese Scholars, State Education Ministry, the Natural Science Foundation of Sichuan Education Bureau under Grant No 2004A181, and the Natural Science Foundation of Yibin University （No 2004Z01）.
文摘Polarizabilities of small Sn （n = 2-8） clusters are calculated by using the higher-order finite-difference pseudopotential density functional method in real space. We find that the polarizabilities of the clusters are considered to be higher than the value estimated from the “hard sphere” model using the bulk static dielectric constant. The computed polarizabilities per atom tend to decrease with the increasing cluster size. The polarizabilities are closely related to the HOMO-LUMO gaps and the geometrical configurations.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10776022 and 10576020, and the Key Project of the National Natural Science of China under Grant No 60436010.
文摘The ground state properties and equation of state of the non-oxide perovstdte-type superconductor MgCNi3 are investigated by first-principles calculations based on the plane-wave basis set with the local density approximation （LDA） as well as the generalized gradient approximation （GGA） for exchange and correlation, which agree well with both theoretical calculations and experiments. Some thermodynamic properties including the heat capacity, the thermal expansion coefficient and the Griineisen parameter for perovskite structure MgCNi3 are obtained. The dependences of these thermodynamic properties on pressure and temperature are given for the first time.
基金supports from the National Natural Science Foundation of China(No.22109171)the Chongqing Talent Program(No.cstc2024ycjh-bgzxm0068))+1 种基金the Science and Technology Research Program of Chongqing Municipal Education Commission(No.KJZD-K202301101)the Natural Science Foundation of Chongqing(No.CSTB2023NSCQ-MSX0315).
文摘Hydrogen energy carrier produced by water electrolysis in alkaline electrolytes is rather meaningful and significant for global sustainability imperatives,while the highpH condition usually leads to a poor reversibility of proton adsorption and desorption that significantly determines the hydrogen-generation activity in hydrogen evolution reaction(HER)process.Herein,we demonstrate a remarkable Ru-Mo solid-solution nanocrystal catalyst in alkaline HER process by a very simple but feasible pyrolysis and alkali leaching strategy.Benefiting from the pinning effect and local chemical-and electronic-structure regulations of Mo solute atoms,an ultra-low overpotential(17.3 mV)and an exceptional stability(>100 h)at the typical current density of 10 mA·cm^(−2)are achieved on the ultrasmall Ru-Mo solid-solution nanocrystal catalyst in 1.0 M KOH electrolyte.Density function theory(DFT)calculations gain an insight into the synergistic effect of neighboring Ru and Mo sites in alkaline HER process,where Mo solute atoms are beneficial for the adsorption and activation of water molecules for proton generation and accumulation due to their rich outermost 4d vacant orbitals,while the energy-favorable Ru sites are responsible for the fast deprotonation kinetics of hydrogen intermediates.Our work may provide an interesting route for the development of efficient and stable solid-solution alloy nanocrystals towards alkaline water electrolysis and beyond.
