Modelling the voltammetric study of intercalation in a host structure: application to lithium intercalation in RuO2

Intercalation process kinetics have been studied theoretically for the case of potential sweep voltammetry. The influence of the thickness (or the particle radius) of the “host” material and the potential sweep rate has been determined between the limits of thin film diffusion and semi-infinite diffusion for a reversible process. Experimental data have been obtained with the cell: RuO₂/LiClO₄-PEO/Li. The theoretical results have been used to calculate the diffusion coefficient of lithium in the “host” structure RuO₂ at 80°C, giving an approximate value of 1.6 × 10^?11 cm² s^?1     

Studies of lithium intercalation in 3R-WS2

The lithium intercalation into the layered dichalcogenide 3R-WS₂ has been investigated by electrochemical reduction and by chemical reaction in n-butyl lithium solution. Essential results are (a) a charge transfer of nearly 0.6e⁻/W in Li_xWS₂, (b) a small increase of the c-axis parameter of about 0.6%, and (c) a high mobility of the Li⁺-ions. The chemical diffusion coefficient of Li⁺-ions is estimated to be 8 × 10⁻⁹ cm² s⁻¹ in the composition range 0 ≤ x ≤ 0.25. The appearance of a structural transformation from 3R-WS₂ to 2H-Li_xWS₂ is interpreted on grounds of instabilities in the interlayer structure.     

Single crystal RuO2/Ti and RuO2/TiO2 interface: LEED, Auger and XPS study

The interactions at the evolving RuO₂/titanium interface have been studied by LEED, AES and XPS. Titanium films of up to 5 monolayers were evaporated onto well ordered and ion sputtered ruthenium dioxide crystal surfaces of (110) and (100) orientation. Stabilization of the surface oxygen content under thermal treatment in UHV (up to 600°C) with increasing titanium coverage was established. After extended (up to 4 h) annealing in O₂ at 600°C an epitaxial ordering of TiO₂ on RuO₂(110) was observed. The (1 × 1) LEED patterns from the epitaxial layer exhibit a reduced background level when compared to the RuO₂ substrate itself. These findings are correlated with the XPS data and are interpreted in connection with the disappearance of the defect RuO₂ phase in the surface layer of the RuO₂. The appearance of the (1 × 2) surface reconstruction at the RuO₂(100)/Ti interface is discussed in the context of maximum cation coordination by oxygen atoms.     

A theoretical study of photoelectron spectra of NbO2, MoO2 and RuO2 by cluster models

DV-Xα calculations have been applied to various small clusters of rutile-family dioxides (NbO₂, MoO₂ RuO₂). It appears that by taking into consideration the potential due to the atomic charges, the density, the ionization cross sections of the energy levels, and by summing the density of states (DOS) of the two different clusters representing surface structures, computations on even small clusters provide information which compares well with the experimental XPS spectra.     

Raman investigation of rutile RuO2

We report the first Raman investigation of the rutile material RuO₂. The four allowed first-order Raman-active phonon modes have been observed and classified. Comparison is made with other rutile materials.     

Dip-coated silver-doped V2O5 xerogels as host materials for lithium intercalation

Vanadium pentoxide xerogels have shown high electrochemical performance in terms of energy content. The high specific energy and high intercalation capability make the materials promising for thin film lithium battery and electrochromic device applications. In order to enhance the rate capabilities of the host we increased the electronic conductivity by doping the V₂O₅ xerogels with silver. Samples were prepared by mixing various amounts of silver powder with V₂O₅ hydrogel. We were able to prepare silver-doped vanadium pentoxide dip-coated thin films with a molar ratio (Ag/V) ranging from 0.005 to 0.5 (Ag_yV₂O₃ with y = 0.01, 0.1 and 1). With the successful doping, the electronic conductivity of V₂O₅ was increased by 2 to 3 orders of magnitude. The insertion capacity of the material was maintained and up to 4 moles of lithium per mole of silver-doped V₂O₅ (XRG) were found to be reversibly intercalated.     

Area-selectively sputtering the RuO2 nanorods array

The RuO₂ nanorods array is grown selectively on the SiO₂-patterned sapphire (SA) wafers using reactive sputtering. The area-selectivity is attributed to an early nucleation of RuO₂ and its fast surface coverage on SA (1 0 0) and (0 1 2), in contrast to the sluggish nucleation on glassy SiO₂ in the initial sputtering period. The growth domain is explored by investigating the temperature windows at sputtering power 40, 50, and 60 W. The low-temperature bound is limited by the mobility of precursors on SiO₂ surface, which enables the precursors to depart before aggregating into a large size to smear the non-growth region. The high-temperature bound is set by the horizontal growth which enlarges the rod width and deteriorates its one-dimensional feature. The temperature window shrinks with increasing sputtering power. The X-ray photoelectron spectra indicate the as-sputtered rod surface is ruthenium rich. The X-ray diffraction analysis shows that RuO₂ growth on SA (1 0 0) and (0 1 2) follows the epitaxial relations between RuO₂ and SA crystals.     

Field emission investigations of RuO2-doped SnO2 wires

Field emission studies of a bunch and a single isolated RuO₂:SnO₂ wire have been performed. A current density of 5.73 × 10⁴ A/cm² is drawn from the single wire emitter at an applied field of 8.46 × 10⁴ V/μm. Nonlinearity in the Fowler-Nordheim (F-N) plot has been observed and explained on the basis of electron emission from both the conduction and the valence bands of the semiconductor. The current stability recorded at the preset value of 1.5 μA is observed to be good. Overall the high emission current density, good stability and mechanically robust nature of the RuO₂:SnO₂ wires offer advantages as field emitters for many potential applications.     

Lithium intercalation in LixZrS2

We report electrochemical and x-ray diffraction studies of LixZrS₂. lT-ZrS₂ undergoes a reversible first order transition to the 3R polytype when intercalated with lithium. Co-existing 1T and 3R phases are observed for 0.01 ± 0.01 < x < 0.23 ± 0.01.     

Infrared studies of lithium intercalation in the FePS3 and NiPS3 layer-type compounds

Infrared spectra (700-30 cm^-1) of several lithium intercalates (chemically prepared) Li_xMPS₃, with M=Fe, Ni and 0<x<1.5, have been recorded and compared with those known for the corresponding host lattices. These lithium intercalates are mainly characterized by new absorption bands at 336 cm^-1 and 310 cm^-1 for the iron and nickel compounds, respectively. These bands assigned to lithium vibrations increase progressively with lithium content : it is concluded that Li⁺ ions are more likely to occupy the 2d and 4h “octahedral” sites in the gaps. In addition, the spectra of the nickel derivatives reveal some geometric distortion within the layers and a progressive strengthening of the Ni-S interactions. These results are correlated to the best energy yields obtained in NiPS₃/lithium batteries.     

X-ray and UV photoelectron spectra of the oxides NbO2, MoO2 and RuO2

HeI and Mg Kα_1,2 valence band photoelectron spectra of polycrystalline samples of NbO₂, MoO₂ and RuO₂ are reported. A marked increase is observed in the intensity of the metal 4d structure, relative to that due to oxygen 2p electrons, on changing from X-ray to UV excitation. The superior resolution of the 4d signals in the HeI spectra reveals the presence of the Fermi edge in the metallic oxides MoO₂ and RuO₂. In addition, the HeI spectrum of MoO₂ shows a splitting of the metal 4d signal, confirming established ideas concerning the electronic structure of such materials.     

Characterization of RuO2 thin films by Raman spectroscopy

Raman scattering has been used as a technique for the characterization of RuO₂ thin films deposited on different substrates by the metal-organic chemical vapor deposition method and reactive sputtering under various conditions. Red shift and broadening of the linewidth of the Raman peaks are analyzed by the spatial correlation model. The intrinsic linewidth for the RuO₂ films deposited at high and low temperatures has to be adjusted to different values to achieve a good fit for the features. The lineshape and position of the Raman features vary for films deposited on different substrates under the same condition. These differences indicate the existence of stress induced by lattice mismatch and the differential thermal expansion coefficients between RuO₂ and the substrates. After annealing at 650°C in an oxygen atmosphere for 3 h, the linewidth decreases significantly for the RuO₂ thin films deposited at lower temperatures. The results show the improvement of the crystallinity of the films during the annealing process.     

Electronic and thermodynamic and elastic properties of pyrite RuO2

This paper calculates the elastic,thermodynamic and electronic properties of pyrite (P a3ˉ) RuO2 by the plane-wave pseudopotential density functional theory (DFT) method.The lattice parameters,normalized elastic constants,Cauchy pressure,brittle–ductile relations,heat capacity and Debye temperature are successfully obtained.The Murnaghan equation of state shows that pyrite RuO2 is a potential superhard material.Internal coordinate parameter increases with pressure,which disagrees with experimental data.An analysis based on electronic structure and the pseudogap reveals that the bonding nature in RuO2 is a combination of covalent,ionic and metallic bonding.A study of the elastic properties indicates that the pyrite phase is isotropic under usual conditions.The relationship between brittleness and ductility shows that pyrite RuO2 behaves in a ductile matter at zero pressure and the degree of ductility increases with pressure.     

A comparative study of lithium and sodium insertion into HfMo2O8 and two polymorphs of ZrMo2O8

Lithium and sodium insertion into RMo₂O₈ (R = Zr,Hf) has been studied by galvanostatic chronopotentiometry, cyclic voltammetry (CV) and quantitative XRD phase analysis as well as by flame photometry after treatment with n-butyllithium or sodium naphtalide solutions. Low-temperature modification of ZrMo₂O₈ with monoclinic framework structure accommodates two lithiums, in agreement with the topological analysis based on the Voronoi tessellation, at a constant open-circuit voltage of 2.4 V and discharge voltage of ca. 2.1 V. According to CV, the process is partially reversible, but lithium extraction is kinetically hindered, presumably due to the low electronic conductivity of the oxidized phase. Further lithium insertion results in complete amorphization at 4Li per formula unit. This value is limiting also for the isostructural trigonal layered phases, HfMo₂O₈ and high-temperature ZrMo₂O₈; in those cases, however, amorphization starts from the beginning of reduction. Sodium insertion (both electrochemical and chemical) in the three phases is sterically hindered and could only be detected by CV.     

光沉积Ru和RuO2的锐钛矿TiO2纳米片的光解水产氧

采用水热法以HF作为结构调控剂合成了主要暴露（001）面的锐钛矿TiO₂纳米片,通过光沉积方法分别合成了负载Ru和RuO₂物种的光催化剂。利用X射线衍射、透射电镜和氢气程序升温还原等分析表征了催化剂的结构性质。通过光解水产氧反应来研究催化剂的催化性能,详细考察了Ru含量、负载方式以及氧化和还原处理等因素的影响,光解水产氧速率的差异证明了Ru物种在不同晶面的电荷-空穴分离效应。与负载单一助催化剂的Ru/TiO₂和RuO₂/TiO₂样品相比,活性最优的0.5%Ru-1.0%RuO₂/TiO₂样品由于负载了双助催化剂,其催化活性得到更大的提高,证实了在锐钛矿TiO₂上的晶面电荷-空穴分离效应.     

插层化合物Ag1/4TiSe2电子结构的第一性原理研究

采用基于密度泛函理论的平面波赝势方法,选用局域密度近似对Ag_1/4TiSe₂及TiSe₂的几何结构进行了优化和总能量计算.计算得到的晶格常量与实验结果符合较好,负的形成能表明有序Ag_1/4TiSe₂系统的稳定性.布居数、键长、能带结构和态密度的计算结果显示：Ag以较强的离子性结合于Ag_1/4TiSe₂中.Ag的插入使得半金属性的TiSe_{2关键词： 1/4}TiSe₂')" href="#">Ag_1/4TiSe₂ 电子结构 插层化合物 第一性原理计算     

ESR study of lithium incorporation by V2O5 single crystals

Lithium has been chemically and electrochemically incorporated into V₂O₅ single crystals. The ESR spectra of these room temperature bronzes are characterized by the same g tensor as α-Li_xV₂O₅ high temperature bronzes. This suggests that V₂O₅ acts as a three-dimensional framework host and that lithium is inserted into the channels of the orthorhombic structure. However, Li⁺ ions are not randomly distributed into the lattice. A clustering of the paramagnetic centers surrounding these ions is observed, giving an exchange narrowed ESR signal. The usual 29 hyperfine line ESR spectrum of high temperature α-Li_xV₂O₅ is again observed after heating the crystal above 300°C showing that these new bronzes convert to the previously reported Li_xV₂O₅ bronzes.     

Structural evolution of the MoO3(010) surface during lithium intercalation

Atomic force microscopy (AFM) has been used to characterize the structural evolution of the MoO₃(010) surface during the initial stage of Li⁺ intercalation. Lithiation was observed in situ using model cells comprised of a single crystal MoO₃ cathode, a dilute propylene carbonate (PC)-based electrolyte, and an Li metal anode. The insertion of Li⁺ into MoO₃ results in the topotactic nucleation and growth of acicular Li_xMoO₃ (x0.25) precipitates at the (010) surface. Because the interlayer spacing of Li_xMoO₃ (d=7.88 Å) is greater than that of MoO₃ (d=b/2=6.93 Å), the Li_xMoO₃ precipitates expand out of the (010) surface as they grow into the MoO₃ crystal along 010. The local strain associated with this expansion causes the Li_xMoO₃ precipitates to crack parallel to the MoO₃001 and 010 axes once their height exceeds approximately 20 nm. With continued Li⁺ intercalation, cracking becomes more prominent, and the (010) surface begins to fragment and disintegrate. Anisotropies in Li⁺ ion uptake and the influence of surface morphology on Li_xMoO₃ precipitation and crack propagation are described.     

Salting-out in intercalation compounds: Removing copper from Cu3Mo6S8 by intercalating lithium

We study the removal of the copper in Cu₃Mo₆S₈ by the intercalation of lithium. For 0<×<1, Li_xCu₃Mo₆S₈ is a single phase compound. For x?1, the copper atoms are forced out of the Mo₆S₈ host. We present a lattice-gas model which shows how the intercalation of Li can force the Cu out of the host.     

A comparative study of microstructure of RuO2 nanorods via Raman scattering and field emission scanning electron microscopy

Raman scattering (RS) and field emission scanning electron microscopy (FESEM) have been used to extract microstructural information of RuO₂ nanorods (NRs) and a two-phase system comprising NRs embedded in polycrystalline matrix deposited on different substrates by the metal-organic chemical vapor deposition method. The red shifts and asymmetric broadening of the Raman line shape for the NRs are analyzed by the spatial correlation model. The deduced spatial correlation length l is found to be much smaller than that of the average size L₀ estimated from the FESEM images. The Raman features for the two-phase system can be resolved into two parts: a Lorentzian line shape feature corresponding to the polycrystallite at higher frequency side and an asymmetrically broadened NRs' signature located at lower frequency end. The volume fraction of NRs in the two-phase system can be determined from the analysis. These results demonstrate the significance of RS as a structural characterization method when used in conjunction with FESEM.