The theoretical study of O<Subscript>2</Subscript> adsorption on NiTi (100) and (110) surfaces

The discrete variational Xa method (DV-Xα) within the framework of density-functional theory was applied to study O₂ molecule adsorption on NiTi (100) and (110) surfaces. The bond order and charge distribution between Ti and O atoms for two possible O₂ molecule adsorption ways on NiTi (100) and (110) surfaces were calculated. It is found that the adsorption way for O−O bond perpendicular to NiTi surface is preferred to that for O−O bond parallel to NiTi surface, and O₂ molecule only interacted with one nearest surface titanium atom during the adsorption process. Mulliken population and the partial density of state analysis show that the interaction between Ti and O atoms is mainly donated by O 2p and Ti 4s electrons on NiTi(110) surface, O 2p and Ti 4s, 4p electrons on NiTi(100) surface, respectively. The total density of state analysis shows that NiTi(100) surface is more favorable for O₂ molecule adsorption. HUA Ying-jie: Born in 1966. Funded by the National Natural Science Foundation of China (No. 50081001)     

InSb(110)弛豫表面电子态的计算

利用形式散射理论方法，采用最近邻的紧束缚模型计算了ＩｎＳｂ（１１０）弛豫表面的电子结构，给出了总体、局域、分波态密度和表面投影能带。通过分析其表面态的变化指出了表面发生弛豫的原因主要是阴阳离子的ｐ态电子的相互作用加强所产生的。     

Theoretical calculation and experimental study of influence of oxygen vacancy on the electronic structure and hemocompatibility of rutile TiO2

In this work, the relationship between electronic structure and hemocompatibility of oxygen deficient rutile TiO_2?x was studied by both theoretical calculation and experimental study. Based on the local density functional theory, first-principals method was performed to calculate the electronic structure of rutile TiO₂ with different oxygen vacancy concentration. In the range of less than 10% of (or equal) physically realistic O vacancy concentration, the band gap of rutile TiO₂ increases with increasing O vacancy concentration, leading the TiO₂ changes from a p-type to an n-type semiconductor. The valance band of TiO₂ is predominated by O 2p orbital, while the conduction band is occupied by Ti 3d orbital for different O vacancy concentration. The O vacancy results in the occupation of electrons at the bottom of conduction band of TiO₂, and the donor density increases with increasing O vacancy concentration. When materials come in contact with blood, the n-type semiconductor feature of oxygen deficient TiO_2?x with the bottom of conduction band occupied by electrons would prevent charge transfer from fibrinogen into the surface of materials, thus inhibiting the aggregation and activation of platelets, therefore improving the hemocompatibility of rutile TiO_2-x .

     

Theoretical calculation and experimental study of influence of oxygen vacancy on the electronic structure and hemocompatibility of rutile TiO2

In this work, the relationship between electronic structure and hemocompatibility of oxygen deficient rutile TiO_2−x was studied by both theoretical calculation and experimental study. Based on the local density functional theory, first-principals method was performed to calculate the electronic structure of rutile TiO₂ with different oxygen vacancy concentration. In the range of less than 10% of (or equal) physically realistic O vacancy concentration, the band gap of rutile TiO₂ increases with increasing O vacancy concentration, leading the TiO₂ changes from a p-type to an n-type semiconductor. The valance band of TiO₂ is predominated by O 2p orbital, while the conduction band is occupied by Ti 3d orbital for different O vacancy concentration. The O vacancy results in the occupation of electrons at the bottom of conduction band of TiO₂, and the donor density increases with increasing O vacancy concentration. When materials come in contact with blood, the n-type semiconductor feature of oxygen deficient TiO_2−x with the bottom of conduction band occupied by electrons would prevent charge transfer from fibrinogen into the surface of materials, thus inhibiting the aggregation and activation of platelets, therefore improving the hemocompatibility of rutile TiO_2-x . Supported by the National Basic Research Program of China (Grant No. 2005CB623904), National High-Tech Research Program of China (Grant No. 2006AA02A139) and National Natural Science Foundation of China (Grant No. 20603027)     

Effect of Nb on plasticity and oxidation behavior of TiAlNb intermetallic compound by density functional theory

Based on the pseudo potential plane-wave method of density functional theory (DFT), Ti_1−x Nb _x Al ( _x =0, 0.062 5, 0.083 3, 0.125, 0.250) crystals’ geometry structure, elastic constants, electronic structure and Mulliken populations were calculated, and the effects of doping on the geometric structure, electronic structure and bond strength were systematically analyzed. The results show that the influence of Nb on the geometric structure is little in terms of the plasticity, and with the increase of Nb content, the covalent bond strength remarkably reduces, and Ti-Al, Nb-M (M=Ti, Al) and other hybrid bonds enhance; meanwhile, the peak district increases and the pseudo-energy gap first decreases and then increases, the overall band structure narrows, the covalent bond and direction of bonds reduce. The population analysis also shows that the results are consistent with the electronic structure analysis. The density of states of TiAlNb shows that Nb doping can enhance the activity of Al and benefit the form of Al₂O₃ film. All the calculations reveal that the room temperature plasticity and the antioxidation properties of the compounds can be improved with the Nb content of 8.33%–12.5% (mole fraction).     

Microstructures and wear resistance of chromium coatings on P110 steel fabricated by pack cementation

In order to obtain a high-performance surface on P110 steel that can meet the requirements in oil/gas field environment, the chromium coatings were fabricated by pack cementation. The chromium coatings differed in with/without the addition of La₂O₃. Scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD) and microhardness tester were employed to investigate the surface morphologies, surface element distributions, microstructures, phase constitutions and microhardness of the coatings. Friction-wear tests of the P110 steel substrate and the coatings were conducted in air at ambient temperature and humidity. The results show that uniform and continuous coatings are formed on P110 steel regardless of adding La₂O₃ or not. The chromium coatings consist of Cr₂₃C₆, Cr₇C₃, and (Cr, Fe)₇C₃. The La₂O₃-added chromium coating is more beneficial in terms of surface morphology, microstructure, thickness and microhardness as compared with the coating without adding La₂O₃. Chromizing treatment significantly improves the surface hardness and wear resistance of the P110 steel. The wear resistance of the tested samples can be sorted in the following sequence: La₂O₃-coating>no RE-coating>bare P110 steel.     

Preparation and characteristics of Cu/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/MgF<Subscript>2</Subscript>/Au tunnel junction

The fabrication process of Cu/Al₂O₃/MgF₂/Au double-barrier metal/insulator/metal junction (DMIMJ) was introduced, and more stable light emission from this junction was successfully observed. The light emission physical mechanism of the junction was discussed. Results show that light emission spectrum of this structure locates at wavelength of 250–700 nm with two peaks at around 460 nm and 640 nm, which moves towards shorter wavelength region in comparison with that of the Al/Al₂O₃/Au junction. The light emission efficiency of this junction ranges from 0.7×10⁻⁵–2.0×10⁻⁵, which is 1 to 2 orders higher than that of the single-barrier Al/Al₂O₃/Au junction. The improved properties of this structure should be due to the electrons resonant tunneling effect in the double-barrier.     

Calculated structure, elastic and electronic properties of Mg2Pb at high pressure

The effects of high pressure on structure,elastic and electronic properties of the intermetallic Mg₂Pb were calculated by the first-principles plane wave pseudo-potential method in the scheme of density functional theory（DFT）within the generalized gradient approximation.The elastic constants and Debye temperature obtained at 0 GPa are in good agreement with the available experiment data and other theoretical results.The electronic properties calculated suggest that the electronic density of states（DOS）at the Fermi level decreases under high pressure.     

Tunable electronic and magnetic properties from structure phase transition of layered vanadium diselenide

The atomic geometry, structure stability, electronic and magnetic properties of VSe₂ were systematically investigated based on the density functional theory (DFT). Varying from 3D to 2D four VSe₂ structures, bulk 2H-VSe₂ and 1T-VSe₂, monolayer H-VSe₂ and T-VSe₂ are all demonstrated as thermodynamically stable by lattice dynamic calculations. More interestingly, the phase transition temperature is dramatically different due to the lattice size. Finally, owing to different crystal structures, H-VSe₂ is semimetallic whereas T-VSe₂ is totally metallic and also they have different magnetic moments. Our main argument is that being exfoliated from bulk to monolayer, 2H-VSe₂ transforms to T-VSe₂, accompanied by both semimetallic-metallic transition and dramatic magnetic moment variation. Our calculations provide a novel structure phase transition and an efficient way to modulate the electronic structure and magnetic moment of layered VSe₂, which suggests potential applications as high-performance functional nanomaterial.     

Electrochemical Characterization of Surface-modified LiMn2O4 Cathode Materials for Li-ion Batteries

To improve the performance, the surface of 12Mn2O4 was coated with very fine MgO , Al2O3 and ZnO by solgel method, respectively. The structure and morphology of the coated materials were investigated by X-ray diffraction （ XRD ）, X-ray photoelectron spectroscopy （ XPS ） and scanning electron microscopy （SEM）. The charge and discharge performance of uncoated and surfnce modified 12Mn2O4 spinel at 25℃ and 55 ℃ were tested, using a voltage window of 3.0-4.35 V and a current deasity of 0. 1 C rate. There is a slight decrease in the initial discharge capacity relative to that of uncoated UMn2 O4, bat the cycle ability of 12 12Mn2O4 coated by metal-oxide has remarkably been improved. The EIS measuremeuts of uncoated and Al2O3 -coated 12Mn2O4 were carried out by a model 273 A potentiostatl galvanistat controUed by a computer using M270 software, and using a freqnency response analyzer （ Zsimpwin ） combined with a potentiostate （ PAR 273）. Coaseqnently, the reason for the improved cycle properties is that the surface modification reduces the dissolution of Mn , which results from the suppression of the electrolyte decomposition, and suppresses the formation of passivation film that acts as an electronic insulating layer. In conclusion, the use of surface modification is an effective way to improve the electrochemical performance of 12Mn2O4 cathode material for lithium batteries.     

Segregation modes,characteristics, and mechanisms of multi-component lignite in a vibrated gas-fluidized bed

The segregation modes and characteristics of 1-6 mm multi-component lignite were studied in a microporous, vibrated, gas-fluidized bed of Φ110 mm ×400 mm. The effects of particle density and size, vibration frequency and amplitude, and gas velocity on these characteristics were considered. The average size, average density, size deviation coefficient, and density deviation coefficient were used to identify lignite size and density. The separation efficiency was adopted to evaluate the segregation performance,and the segregation mechanisms were explored. The results show that ε(size,max) of heterogeneous multisize-component lignite with K_(size) = 65% reaches 80% at f= 20 Hz, A = 5 mm, and N =(1,3). ε_(density,max) Of heterogeneous multi-density-component lignite with K_(density)= 25% reaches 50% at f = 15 Hz, A = 5 mm,and N =(1,1.5). The density segregations of 1-3 and 3-6 mm multi-component mixtures are remarkable,ε_(density,max)= 42% and 31% at f= 14 and 16 Hz, and A = 3 and 5 mm, respectively. The size segregation of 1-6 mm multi-component mixture is prominent and ε_(size,max)= 55% at f= 15 Hz, A = 5 mm. The mediumsized mixture with a narrow size distribution at low frequency is favorable for density segregation,and a mixture with a wider size distribution at high frequency is most favorable for size segregation.Precise control of gas flow and vibration as well as optimal design of the fluidized bed can improve the performance of segregation in the vibrated gas-fluidized bed.     

Electronic Structure and Optical Properties of LiBiO<Subscript>3</Subscript> Doped with V,Nb, and Ta

The crystal structure, band structure, density of states, Mulliken charge, bond population and optical properties for LiBi_1-xM_xO₃ (M=V, Nb, and Ta) were investigated using hybrid density functional theory. It was found that LiBiO₃ doped with V, Nb, and Ta presented distinctly stronger covalent interactions in M-O (M=V, Nb, and Ta) than Bi-O, thus resulting in mild distortion of the structure and facilitating the separation of photogenerated carriers. Furthermore, the hybridizations of Bi-6s, M-d (M=V, Nb, and Ta) and O-2p widened the valence and conduction bands, which promoted transmission of photogenerated carriers in the band edge and thus caused better photocatalytic performance.     

Bacteria adherence properties of nitrogen-doped TiO2 coatings by plasma surface alloying technique

In order to obtain a high-performance surface on 316L stainless steel (S. S) that can meet the requirements in medical material field environment, nitrogen-doped titanium dioxide (TiO2-xNx) was synthesized by oxidative annealing the resulted TiNx coatings in air. Titanium nitride coatings on 316L S. S were obtained by plasma surface alloying technique. The as-prepared coatings were characterized by X-ray diffraction, glow discharge optical emission spectrometer (GDOES), scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The bacteria adherence property of the TiO2-xNx coatings on S. S on the oral bacteria Streptococcus Mutans was investigated and compared with that of S. S by fluorescence microscopy. The mechanism of the bacteria adherence was discussed. The results show that the TiO2-xNx coatings are composed of anatase crystalline structure. SEM measurement indicates a rough surface morphology with three-dimensional homogenous protuberances after annealing treatment. Because of the photocatalysis and positive adhesion free energy, the TiO2-xNx coatings inhibit the bacteria adherence.     

Synergetic strengthening mechanism of ultrasound combined with calcium fluoride towards vanadium extraction from low-grade vanadium-bearing shale

The effect and mechanism of ultrasound and CaF₂ on vanadium leaching from vanadium-bearing shale were investigated systematically. In consideration of the enhancement for vanadium recovery, the combination of ultrasound and CaF₂ (66.28%) exerts more evident effects than ultrasound (26.97%) and CaF₂ (60.35%) alone, demonstrating the synergetic effect of ultrasound and CaF₂. Kinetic analysis manifests that the product layer diffusion controls vanadium leaching in ultrasound system without CaF₂, however product layer diffusion and interfacial reaction is the rate-controlling step for vanadium leaching in other three leaching systems. The combination of ultrasound and CaF₂ notably decreases the activation energy (E_a) from 62.03 to 27.61 kJ/mol, nevertheless individual CaF₂ only reduces the E_a to 50.70 kJ/mol. X-ray diffraction and fourier transform infrared spectrometer analyses show that the decomposition degree of the vanadium-bearing mica structure is the most significant in ultrasound and CaF₂ system, proving the highest release degree of vanadium. Specific surface area and pore distribution combined with scanning electron microscope analyses reveal that the action of ultrasound and CaF₂ would provide higher specific surface area, more abundant pores structure and cracks for the particles, which further prompts the rapid diffusion of H⁺, F⁻ and HF, and achieves the conspicuous improvement of vanadium leaching recovery.     

Theoretical studies of structures and spectroscopic properties of [(tpy)(bpy)RuC≡CC_6H_4R]~+(tpy = 2,2′:6′,2″-terpyridine,bpy = 2,2′-bipyridine; R = F,Cl, H,Me and OMe)

A series of polypyridine ruthenium(II)acetylide complexes,[(tpy)(bpy)RuC≡CC6H4R]+(tpy=2,2′:6′,2″-terpyridine,bpy=2,2′-bipyridine;R=F(1),Cl(2),H(3),Me(4)and OMe(5))are investigated theoretically to explore their electronic structures and spectroscopic properties.Their ground/excited state geometries,electronic structures and spectroscopic properties are first calculated using density functional theory(DFT)and time-dependent DFT(TDDFT).The absorption and emission spectra of the complexes in acetonitrile solution are also obtained by using TDDFT(B3LYP)method associated with the CPCM model.The calculations show that the energy levels of HOMOs for 1–5 are sensitive to the substituent on phenylacetylide ligand and increase with the same order of the electron-donating ability of the substituents;however,those of polypyridine-based LUMOs vary slightly.The lowest-energy absorptions and emissions for 1–5 are progressively red-shifted in the order of 1≈2345 when the electron-donating groups are introduced into the phenylacetylide ligand.The phosphorescence of 1 are attributed to{[dxz(Ru)+π(C≡C)]→[π*(tpy)]}(3MLCT/3LLCT)transition,whereas those of 2–5 are originated from{[dxz/dxy(Ru)+π(C≡C)+π(C6H4R)]→[π*(tpy/bpy)]}(3MLCT/3LLCT)transitions.     

Microstructure and corrosive property of Ni-P/nano-CeO<Subscript>2</Subscript> coating electrolessly prepared in acidic condition

Electroless Ni-P/nano-CeO₂ composite coating was prepared in acidic condition, and its microstructure and corrosive property were compared with its CeO₂-free counterpart. Scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and differential scanning calorimeter (DSC) were used to examine surface morphology and microstructure of the coating. Aqueous corrosion was done in 3%NaCl+5%H₂SO₄ solution and high temperature oxidation was done at 750 °C in air. The results showed that Ni-P coating had partial amorphous structure mixed with nano-crystals, while the Ni-P/CeO₂ coating had perfect amorphous structure. At high temperature, Ni3P precipitation and Ni crystallization took place in both coatings at different temperatures. Aqueous corrosion property and high temperature oxidation property of the composite coating were remarkably improved due to the coating’s microstructure change and the rare earth doping effect. During the co-deposition process, some Ce ⁿ⁺(n=3, 4) ions may be adsorbed to metal/solution interface and hinder nickel deposition. Ni-P/CeO₂ coating’s perfect amorphous structure results from the hindered crystal- typed deposition of nickel and the promoted deposition of phosphorous.     

Effect of oxygen partial pressure on epitaxial growth and properties of laser-ablated AZO thin films

Al-doped ZnO (AZO) thin films were grown on c-sapphire substrates by laser ablation under different oxygen partial pressures (P _O2). The effect of PO2 on the crystal structure, preferred orientation as well as the electrical and optical properties of the films was investigated. The structure characterizations indicated that the as-grown films were single-phased with a wurtzite ZnO structure, showing a significant c-axis orientation. The films were well crystallized and exhibited better crystallinity and denser texture when deposited at higher P _O2. At the optimum oxygen partial pressures of 10 - 15 Pa, the AZO thin films were epitaxially grown on c-sapphire substrates with the (0001) plane parallel to the substrate surface, i e, the epitaxial relationship was AZO (000 1) // Al₂O₃ (000 1). With increasing P _O2, the value of Hall carrier mobility was increased remarkably while that of carrier concentration was decreased slightly, which led to an enhancement in electrical conductivity of the AZO thin films. All the films were highly transparent with an optical transmittance higher than 85 %.     

Kinetic study of LiMn2O4 in process of lithium intercalation

Exchange current density of spinel LiMn₂O₄ was studied by linear polarization. The relationship of the kinetic property with the structure of spinel LiMn₂O₄ was investigated by studying the effect of the doping and surface coating on the kinetic properties of electrode material. The results show that the exchange current density of spinel LiMn₂O₄ electrode increases with the increase of the amount for lithium intercalation at first, and then decreases. The maximal exchange current density appeares at the 80%–90% lithium intercalation. The similar phenomenon was observed on the doped spinel LiMn₂O₄ electrode. Doping can enhance the exchange current density of spinel LiMn₂O₄ material. However, the degree of the doping effect varies with the doped element varying. Surface coating can also enhance the exchange current density of spinel material, and the increment of value is higher than that of doped ones. Foundation item: Project(50302016) supported by the National Natural Science Foundation of China     

First-principles investigation of the phase stability of MgAl2 compounds

First-principles have been calculated to investigate the phase stabilities of the intermetallic phase of MgAl2 compounds by electronic structures and the charge distribution maps.The first-principles e...     

First-principles study on adsorption of Au atom on hydroxylated SiO<Subscript>2</Subscript> surface

Adsorption of single gold (Au) atom at three kinds of sites (hollow, bridge and top) on the hydroxylated β-cristobalite SiO2 (1 1 1) surface was studied using the first-principles calculations with general gradient approximation (GGA). The results of adsorption energies and density of electronic states (DOS) suggest that the hollow and bridge sites have the basically equal capability of binding Au, while the ability of the Top site is weaker. Two new energy levels emerge after the adsorption at all sites; i...