Improved electrochemical performance of Li(Ni_(0.6)Co_(0.2)Mn_(0.2))O_2 at high charging cut-off voltage with Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3 surface coating

Ba_(0.8)Sr_(0.2)FeO_(3-δ)has been surface-modified by the lithium-ion conductor Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3via a facile mechanical fusion method. The annealing temperature during coating process shows a strong impact on the surface morphology and chemical composition of Li(Ni_(0.6 )Co_(0.2) Mn_(0.2))O2_. The 600-?C annealed material exhibits the best cyclic stability at high charging cut-off voltage of 4.5 V(versus Li~+/Li) with the capacity retention of 90.9% after 100 cycles, which is much higher than that of bare material(79%). Moreover, the rate capability and thermal stability are also improved by Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3coating. The enhanced performance can be attributed to the improved stability of interface between Ba_(0.8)Sr_(0.2)FeO_(3-δ)and electrolyte by Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3modification. The results of this work provide a possible method to design reliable cathode materials to achieve high energy density and long cycle life.     

Effect of the stoichiometry on the electronic structure of the Ni（111）/α-Al2O3（0001） interface： a first-principles investigation

In this paper first-principles calculations of Ni（111）/α-Al2O3（0001） interfaces have been performed, and are compared with the preceding results of the Cu （111）/α-Al2O3（0001） interface [2004 Phil. Mag. Left. 84 425]. The AI- terminated and O-terminated interfaces have quite different adhesion mechanisms, which are similar to the Cu（111）/α Al2O3（0001） interface. For the O-terminated interface, the adhesion is caused by the strong O-2p/Ni-3d orbital hybridization and ionic interactions. On the other hand, the adhesion nature of the Al-terminated interface is the image-like electrostatic and Ni-Al hybridization interactions, the latter is substantial and cannot be neglected. Charge transfer occurs from Al2O3 to Ni, which is opposite to that in the O=terminated interface. The charge transfer direction for the Al-terminated and O-terminated Ni（111）/α-A1203（0001） interfaces is similar to that in the corresponding Cu（111）/α- Al2O3（0001） interface, but there exist the larger charge transfer quantity and consequent stronger adhesion nature, respectively.     

Adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co （200）： A first-principles density-functional study

First-principles calculations based on density functional theory are used to investigate the adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co(200). The preferred site for the carbon atom on the surface is the hollow site, and the preferred site in the subsurface is the octahedral site. There is charge transfer from the surface to the adsorbed carbon atom, and for the most favorable adsorbed structure the charge transfer is largest. Moreover, the energy barriers for the diffusions of carbon atoms on the surface and from the surface into the subsurface and then back to the surface are calculated in detail. The results indicate that the energy barrier for the diffusion of carbon atoms on the surface is comparable to that from the subsurface to the surface. The results imply that both the direct surface nucleation and the surface segregation from Co bulk can be observed in the chemical vapor deposition growth of graphene on Co(200)substrate, which can gain a new insight into the growth mechanism of graphene.     

Na+替位掺杂对Li2MnSiO4的电子结构以及Li+迁移过程的影响

在锂二次电池中, 硅酸锰锂作为正极材料得到广泛研究, 但其固有的电子和离子电导率较低, 直接影响着电池的功率密度和充放电速率. 本文建立了不同浓度的Na⁺离子替位掺杂Li⁺离子形成的Li_1-xNa_xMnSiO₄(x=0, 0.125, 0.25, 0.5)结构, 采用第一性原理的方法, 研究了掺杂前后硅酸锰锂的电子结构以及Li⁺离子的跃迁势垒. 发现在Li⁺位替代掺杂Na⁺, 导带底的能级向低能方向发生移动, 降低了Li₂MnSiO₄ 材料的禁带宽度, 有利于提升材料的电子导电性能. 随着掺杂浓度的升高, 禁带宽度逐渐变窄. CI-NEB结果表明, 在Li₂MnSiO₄体系中具有两条有效的Li⁺离子迁移通道, 掺杂Na⁺以后扩大了Li⁺ 离子在[100]晶向上的迁移通道, Li⁺离子的跃迁势垒由0.64 eV降低为0.48, 0.52和0.55 eV. 掺杂浓度为 x=0.125时, 离子迁移效果最佳. 研究表明Na⁺掺杂有利于提高Li₂MnSiO₄材料的离子和电子电导率.     

Na原子在Si(111)-(7×7)表面的吸附:从二维原子气到纳米团簇阵列

作者利用扫描隧道显微镜 (STM)详细研究了室温下Na原子在Si(111) (7× 7)表面的吸附 .对STM图像及功函数变化的分析表明 ,当Na原子覆盖度小于临界覆盖度 (0 .0 8ML)时 ,Na原子具有类气态的性质并可以在一个吸附能阱中快速移动 .从STM图像可看出这种移动导致的对比度调制 .在临界覆盖度以上 ,Na原子自组装形成团簇阵列 .第一原理模拟计算的结果与作者的实验结论很好吻合 .     

Mg掺杂对Li(Co,Al)O2电子结构影响的第一原理研究

基于密度泛函理论的第一原理赝势法，研究了Mg在Li(Co，Al)O2中掺杂前后的电子结构的变化.通过能带和态密度的分析,发现Mg掺杂后在价带中引入了电子空穴，同时价带展宽，这两个电子结构的显著变化是引起Li(Co，Al)O2导电率提高的主要机理.通过对Co3d电子态密度的分析发现，在二价Mg掺杂后，Li(Co，Al)O2中的Co价态升高，介于Co3+和Co4+之间.从能带计算出发，进一步定量给出了Co和O的平均价态的变化. 关键词： Li(Co Al)O2 电子结构 第一原理 电导     

Structural,electronic, optical and elastic properties of the complex K2PtCl6-structure hydrides ARuH6 (A = Mg,Ca, Sr and Ba): first-principles study

We report a systematic study of the structural, electronic, optical and elastic properties of the ternary ruthenium-based hydrides A₂RuH₆ (A = Mg, Ca, Sr and Ba) within two complementary first-principles approaches. We describe the properties of the A₂RuH₆ systems looking for trends on different properties as a function of the A sublattice. Our results are in agreement with experimental ones when the latter are available. In particular, our theoretical lattice parameters obtained using the GGA-PBEsol to include the exchange-correlation functional are in good agreement with experiment. Analysis of the calculated electronic band structure diagrams suggests that these hydrides are wide nearly direct band semiconductors, with a very slight deviation from the ideal direct-band gap behaviour and they are expected to have a poor hole-type electrical conductivity. The TB-mBJ potential has been used to correct the deficiency of the standard GGA for predicting the optoelectronic properties. The calculated TB-mBJ fundamental band gaps are about 3.53, 3.11, 2.99 and 2.68 eV for Mg₂RuH₆, Ca₂RuH₆, Sr₂RuH₆ and Ba₂RuH₆, respectively. Calculated density of states spectra demonstrates that the topmost valence bands consist of d orbitals of the Ru atoms, classifying these materials as d-type hydrides. Analysis of charge density maps tells that these systems can be classified as mixed ionic-covalent bonding materials. Optical spectra in a wide energy range from 0 to 30 eV have been provided and the origin of the observed peaks and structures has been assigned. Optical spectra in the visible range of solar spectrum suggest these hydrides for use as antireflection coatings. The single-crystal and polycrystalline elastic moduli and their related properties have been numerically estimated and analysed for the first time.     

Structural and electrochemical properties of LiCoO2 and LiAlyCo1−yO2 (y=0.1 and 0.2) oxides: A comparative study of electrodes prepared by the citrate precursor route

We present the characterization and electrode behavior of LiCoO₂ and Al-doped LiAl_yCo_1−yO₂ (y=0.1 and 0.2) oxides prepared by wet-chemical method from the citrate precursor route. We study the phase evolution as a function of the aluminum substitution and the modification on the intercalation and deintercalation of Li ions. Characterization methods include XRD, SEM, and FTIR. X-ray diffraction patterns show that samples belong to the LiCoO₂-LiAlO₂ solid solution and have the layered α-NaFeO₂ structure. FT-infrared vibrational spectroscopy indicates the slight modification in the local structure related to the short-range environment of oxygen coordination around the cations in oxide lattices. The frequencies and relative intensities of the bands are sensitive to the covalency of the (Al, Co)O₂ slabs. The overall electrochemical capacity of the LiAl_yCo_1−yO₂ oxides have been reduced due to the sp metal substitution, however, a more stable charge-discharge cycling performances have been observed when electrodes are charged to 4.3 V as compared to the performances of the native oxide. Differences and similarities between LiCoO₂ and Al-substituted oxides are discussed therefrom. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15–21, 2002.     

N^＋（N=Li,Na,K）对发光材料M3（M=Ca,Sr,Ba）Y2（BO3）4：Eu^3＋光谱的影响

采用高温固相反应方法在空气中制备了M3(M=Ca,Sr,Ba)Y2(BO3)4∶Eu3 红色发光材料,测量结果显示,材料的主发射峰均位于613 nm处,监测613 nm发射峰时,所得材料的激发光谱相同。研究了Li ,Na 和K 对M3(M=Ca,Sr,Ba)Y2(BO3)4∶Eu3 材料激发与发射光谱的影响,结果显示,加入Li ,Na 和K 后,M3(M=Ca,Sr,Ba)Y2(BO3)4∶Eu3 材料的激发与发射光谱的峰值位置并不发生变化,但材料的激发与发射光谱的峰值强度均得到了不同程度的增强。在Li ,Na 和K 掺入浓度相同的条件下,研究发现,与加入Na 和K 时相比,加入Li 时,M3(M=Ca,Sr,Ba)Y2(BO3)4∶Eu3 材料的激发与发射光谱的峰值增强效果最明显。进而研究了Sr3Y2(BO3)4∶Eu3 材料发射峰强度随Li 掺杂浓度的变化情况,结果表明,随着Li 掺杂浓度的增大,Sr3Y2(BO3)4∶Eu3 材料发射峰强度先增大后减小,在Li 浓度为5 mol%时到达峰值,约为未掺杂时的两倍。     

Lithium ion conductivity of Li5+xBaxLa3?xTa2O12 (x?=?0–2) with garnet-related structure in dependence of the barium content

The stoichiometry range and lithium ion conductivity of Li_5+x Ba _x La_3−x Ta₂O₁₂ (x = 0, 0.25, 0.50, 1.00, 1.25, 1.50, 1.75, 2.00) with garnet-like structure were studied. The powder X-ray diffraction data of Li_5+x Ba _x La_3−x Ta₂O₁₂ indicated that single phase oxides with garnet-like structure exist over the compositional range 0 ≤ x ≤ 1.25; while for x = 1.5, 1.75 and 2.00, the presence of second phase in addition to the major garnet like phase was observed. The cubic lattice parameter increases with increasing x and reaches a maximum at x = 1.25 then decreases slightly with further increase in x in Li_5+x Ba _x La_3−x Ta₂O₁₂. The impedance plots of Li_5+x Ba _x La_3−x Ta₂O₁₂ samples obtained at 33 °C indicated a minimum grain-boundary resistance (R _gb) contribution to the total resistance (R _b + R _gb) at x = 1.0. The total (bulk + grain boundary) ionic conductivity increases with increasing lithium and barium content and reaches a maximum at x = 1.25 and then decreases with further increase in x in Li_5+x Ba _x La_3−x Ta₂O₁₂. Scanning electron microscope investigations revealed that Li_6.25Ba_1.25La_1.75Ta₂O₁₂ is much more dense, and the grains are more regular in shape. Among the investigated compounds, Li_6.25Ba_1.25La_1.75Ta₂O₁₂ exhibits the highest total (bulk + grain boundary) and bulk ionic conductivity of 5.0 × 10⁻⁵ and 7.4 × 10⁻⁵ S/cm at 33 °C, respectively.     

Adsorption and diffusion of a Si adatom on the H/Si(1 1 1) surface: comparison with the H/Si(0 0 1) surface

Using a first-principles method, we investigate the adsorption and diffusion of a Si adatom on the H-terminated Si(1 1 1) substrate, which would be useful in understanding the initial stages of Si homoepitaxy using a H surfactant. The adatom substitutes H atom(s) to form a monohydride structure or a dihydride structure. In forming the monohydride structure, the energy barrier for H substitution is absent. The adatom migrates on the surface with alternating its chemical state between monohydride and dihydride. These behaviors of the adatom are quite similar to those on the H/Si(0 0 1)2 × 1 surface, despite the significant difference in the substrate structure between both orientations. The resulting diffusion barrier is 1.30 eV, which is also comparable to that on the H/Si(0 0 1)2 × 1 surface.     

碱金属团簇(Li2F)nM (M=Li,Na, K; n=1, 2)结构、稳定性和红外光谱的理论研究

利用密度泛函理论B3LYP方法和6-311+G*全电子基组对(Li₂F)_nM (M=Li, Na, K; n=1, 2)团簇的几何结构进行了优化,确定了它们的基态结构,并对它们的化学稳定性、电子特性和红外光谱进行了理论研究。结果表明：(Li₂F)M (M=Li, Na, K)团簇具有相似的双三角基态结构,但是(Li₂F)₂M的基态结构则完全不同;(Li₂F)Li和(Li₂F)₂Na团簇具有较大的键能和HOMO-LUMO能隙,致使其具有较高的化学稳定性。通过轨道分析发现,这两个稳定团簇的HOMO和LUMO轨道都是由sp杂化而形成了σ键。同时,也发现(Li₂F)₂K团簇因具有较低的电离势(4.23 eV),可以考虑其为新型的超碱金属化合物。此外,模拟了(Li₂F)_nM团簇的红外振动特征峰,并对主要谱峰的振动模式进行了指认。     

A theoretical analysis of adsorption and dissociation of CH3OH on the stoichiometric SnO2(110) surface

A theoretical analysis based on the Hartree–Fock pseudopotential method and a density-functional theory calculation using a hybrid combination of general gradient approximation with pseudopotential procedure has been carried out to study the adsorption and dissociation of methanol on the stoichiometric SnO₂(110) surface. The dependence of the results upon model system and computing method is discussed. An optimization procedure of adsorbate and substrate atom positions on a six-layer slab model has been selected to characterize the corresponding geometric parameters, adsorption energy and charge-transfer processes related with the molecularly adsorbed CH₃OH and dissociative channels to yield methoxy or methyl fragments. In the high-coverage limit (θ=1), we find that dissociation of the methanol molecule via the heterolytic cleavage of the C---O bond is favoured. At lower coverage (θ=1/2), this channel and the molecularly adsorbed methanol present similar adsorption energies.     

Structural investigations of the xTeO2-(1−x)GeO2 (x=0, 0.2, 0.4, 0.6, 0.8 and 1) tellurite glasses: A composition dependent Raman spectroscopic study

Raman spectra of xTeO₂-(1−x)GeO₂ (x=0, 0.2, 0.4, 0.6, 0.8 and 1) germanium tellurite glasses were measured and analyzed in an effort to follow the structural changes caused by mixing two typical glass formers. Systematic Raman intensity measurements have been performed in an effort to elucidate the composition induced structural changes and a possible mechanism accounting for these changes was proposed. The network structure of the glass is characterized by TeO₄ trigonal bipyramid mixed with TeO₃ trigonal pyramid units, while GeO₄ tetrahedral units are also present. Changing the GeO₂ content results in the conversion of the TeO₄ units to TeO₃ units with a neutral doubly bridged oxygen atom, while the existence of charged terminal oxygen atoms is questionable. The measured relative Raman intensities are semi-quantitatively correlated to the transformation of the TeO₄ trigonal bipyramid to TeO₃ trigonal pyramids.     

Adsorption of 2-chlorophenol on Cu2O(1 1 1)-CuCUS: A first-principles density functional study

First-principles density functional theory and a periodic-slab model have been utilized to investigate the adsorption of a 2-chlorophenol molecule on a CuO(1 1 1) surface with a vacant Cu surface site, namely Cu₂O(1 1 1)-Cu_CUS. Several vertical and flat orientations have been studied. All of these molecular configurations interact very weakly with the Cu₂O(1 1 1)-Cu_CUS surface, an observation which also holds for clean copper surfaces and the Cu₂O(1 1 0):CuO surface. Hydroxyl-bond dissociation assisted by the surface was found to be endoergic by 0.42-1.72 eV, depending predominantly on the position of the isolated H on the surface. In addition, the corresponding adsorbed 2-chlorophenoxy moiety was found to be more stable than a vacuum 2-chlorophenoxy radical by about 0.76 eV. Despite these predicted endoergicities, however, we would predict the formation of 2-chlorophenoxy radicals from gaseous 2-chlorophenol over the copper (I) oxide Cu₂O(1 1 1)-Cu_CUS surface to be a feasible and important process in the formation of PCDD/Fs in the post-flame region where gas-phase routes are negligible.     

A periodic model for the V2O5-TiO2 (anatase) catalyst. Stability of dimeric species

We present periodic DFT calculations to study the structure of the V₂O₅-TiO₂ (anatase) catalyst. Linear and cyclic dimeric V₂O₅ species represent the active phase. The support TiO₂ (anatase) is represented for the perfect (1 0 0) and (0 0 1) surfaces. The maximum interaction between the active phase and the support is favored, and low coverage is assumed. The most stable models allow the compensation of the surface dangling bonds, and can be understood as a continuation of the bulk anatase structure. The more suitable models for studying reactivity possess uncoordinated atoms available for reactivity, such as terminal oxygen atoms in V₂O₅. Relaxation plays an important role in the adsorption systems, and cannot be discarded when modeling the V₂O₅-anatase catalyst.