锂离子电池正极材料LiMnO2的结构稳定性及电化学过程中的相变

LiMnO是同质多相化合物，不同相的结构稳定性差异很大，层状结构的LiMnO2是热力学不稳定的结构，制备相当困难，层状结构的LiMnO2是一类新的锂离子电池正极材料，它的理论比容量为270mAh/g，实际比容量也超过170mAh/g，从该体系材料的合成、结构特点，稳定性以及电化学性能等方面对近几年的研究成果进行综述，分析了该化合物的斜方相比单斜层状结构稳定的内在机制以及稳定单斜层状结构LiMnO2的理论依据，讨论LiMnO2在电池充放电循环过程中的相转变以及今后的发展方向。     

Iron at earth-core conditions

We have carried out electronic structure calculations for iron under high pressure using pseudopotential plane wave methods. There is a controversy regarding the structure of iron at moderate pressures (30–100 GPa) and temperatures (1000–2400 K), with different experiments suggesting different structures, such as orthorhombic, double hexagonal close packed (dhcp), etc. Our earlier calculations using the linear muffin-tin orbital method within atomic-sphere-approximation had argued against the stability of the orthorhombic phase. The more accurate calculations presented here predict qualitatively the same results. We have additionally studied the stability of various phases of Fe at different compressions by calculating phonon frequencies. These rule out the stability of the orthorhombic phase. To validate our zero-temperature electronic-structure results at finite temperature, we have compared the shock Hugoniot and melting properties of iron with the results of our electronic structure calculations. Though we have used simplified models for these estimates, our predictions compare well with the experimental data. We thus propose that these models can be used to obtain the information about the high-pressure melting curves of planetary materials.     

锂离子电池正极材料层状LiMnO2的研究进展

对近年来圆外层状氧化锰锂正极材料的研究进展进行了综述。详细介绍了正交和单斜同质多晶层状氧化锰锂的晶体结构，合成方法及其电化学特性。开发新的合成方法以及多组分掺杂改性以提高英应用性仍是今后．层状氧化锰锂的研究发展方向。     

A new polymorph of Ln polysulfides (Ln = Pr and Nd)

A new polymorph of rare earth polysulfides was synthesized under high temperature-pressure conditions. Its X-ray diffraction patterns were indexed on an orthorhombic unit cell with the lattice constants of a = 0.8025, b = 1.6152 and c = 0.4062 for PrS₂ and a = 0.7977, b = 1.6012 and c = 0.4027 nm, for NdS₂. The calculated densities of the orthorhombic polysulfides are nearly same as those of the allotropic phases with monoclinic symmetry. To compare the stability of the two polymorphs, the Madelung energies of the structures were calculated and that of the monoclinic phase, which is synthesized without applying pressures, was found to be lower than that of the orthorhombic phase.     

Pressure induced structural phase transition in SnS — An ab initio study

The structural behaviour of SnS under pressure has been investigated by first principle density functional calculations of the total energy by the TB-LMTO approach. We find that SnS undergoes a structural phase transition from orthorhombic type to monoclinic type structure around 17 GPa which is in good agreement with the recent experimental study. In addition, the ground state properties are computed and compared with the available results.     

Surface characteristics and photoactivity of silver-modified palygorskite clays coated with nanosized titanium dioxide particles

This paper presents the results of a study in which nanosized titanium dioxide (TiO₂) crystal particles were coated onto the surface of palygorskite fibrous clay which had been modified by silver ions using titanium tetrachloride as a precursor. Coated TiO₂ particles with the anatase structure were formed after calcining at 400 °C for 2 h in air. Various analytical techniques were used to characterize the surface properties of titanium dioxide particles on the palygorskite. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that TiO₂ particles were supported on the surface of the palygorskite clays and their size was in the range of 3–6 nm. The titanium oxide coatings were found to be very active for the photocatalytic decomposition of methylene blue.     

Nanostructured cation distribution in FeNbO4: A synchrotron powder diffraction and transmission electron microscopy investigation

The real structure of FeNbO₄ was determined by a combination of electron microscopy investigations and high resolution synchrotron powder diffraction. It is shown that the order-disorder phase transition from the orthorhombic high-temperature modification (-PbO₂-type structure) to the monoclinic low-temperature modification (wolframite-type structure) of FeNbO₄ is translationengleich and leads to a domain structure that consists of a coherent mixture of the orthorhombic and the monoclinic modification. Domains of the monoclinic phase are separated by antiphase boundaries with an antiphase vector . The real structures of eight different samples have been investigated in terms of domain size and degree of cation ordering by peak-shape analysis and the ratio between integrated intensities of split-structure and fundamental reflections. The obtained real structure is correlated with the conditions of synthesis.     

凹凸棒／烷基糖苷悬浮液流变行为研究

以烷基糖苷（APG）为分散剂,系统研究分散剂的用量对凹凸棒悬浮液流变性的影响,运用等温吸附和Zeta电位测定技术对流变作用机制进行分析,并用六种流变模式对悬浮液的流变曲线进行了拟合,结果表明,随烷基糖苷浓度的增大,悬浮液的塑性粘度出现减小、增加再减小的趋势,其中,烷基糖苷浓度为200mg／L时凹凸棒悬浮液塑性粘度最大,该浓度也是悬浮液由“剪切变稀”向“剪切变稠”的转变点。凹凸棒／烷基糖苷悬浮液的流变曲线符合Herschel Buikley流变模型。     

Spherulitic growth and recrystallization in barium silicate glasses

The growth and recrystallization of spherulites formed in barium disilicate glasses between 700 and 900° C has been studied by electron microscopy and electron diffraction. Spherulites formed at 700° C consist of fibrillar (～ 100 Å diameter) monoclinic crystals in confocal arrangement with preferred crystallographic growth axes. High temperature (900° C) spherulites are composites of radially oriented plate-shaped orthorhombic crystals with lateral growth of epitaxially nucleated fibrillar monoclinic crystals. At intermediate temperatures “axialites”, consisting of a single orthorhombic “midrib” crystal with monoclinic fibrillar side-growths, grow in competition with the low temperature spherulite morphology. The monoclinic fibrillar phase is believed to be an intermediate metastable structure which is able to grow more rapidly than the orthorhombic phase via cellular transformation in the presence of impurities. Brief comparison is made between the observed morphologies and theories for interface instability and cellular crystallization. Recrystallization, induced mainly by the large interfacial area of spherulite fibrils, produces faulted and twinned monoclinic grains which transform slowly to the orthorhombic stable crystal phase. A glassy intercrystalline residue becomes more prominant with grain growth.     

Template-free synthesis of self-assembled Co3O4 micro/nanocrystals

In this article, we have reported the fabrication of various morphological porous Co3O4 by thermal decomposition of cobalt oxalate at open atmospheric conditions. Uniform cobalt oxalate microrods and microneedles were synthesized without using any surfactants or templates in large scale. The cobalt oxalate preparation method was played a crucial role on the crystal structure and its morphology. The as prepared cobalt oxalates and its corresponding cobalt oxides were characterized by using the thermogravimetric analysis, X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM) and nitrogen adsorption analysis. The XRD results indicated that the orthorhombic and monoclinic cobalt oxalates were formed in different experimental conditions. The influence of preparation method of cobalt oxalates and cobalt precursors on the final morphology has been investigated. The M-H loop of the Co3O4 porous microrods and microneedles showed the presence of paramagnetic properties at room temperatures. A plausible mechanism of both cobalt oxalates and Co3O4 formation was proposed based on the experimental results.     

Investigation of the drawing mechanism of UHMWPE fibers

The influence of draw ratios (DR) of gel-spun ultrahigh molecular weight polyethylene (UHMWPE) fibers on resultant morphologies, tensile, degrees of orientation, and crystal phase transition properties were investigated using wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The anisotropic crystalline structure with full concentric circular rings originally shown on the WAXD patterns of the as-prepared and drawn UHMWPE fibers gradually transform into oriented fibers with azimuthal spots on the equator as their DR values increase from 1 to 20, in which their orthorhombic crystals, percentage crystallinity, crystalline orientation, and the birefringence values increase significantly. As evidenced by SEM and WAXD analysis, the chain-folded molecules originally present in kebab crystals of the as-prepared UHMWPE fiber specimens gradually transformed into shish-like crystals with relatively high orientation as their DR values increase from 1 to 20. In contrast, the crystallinity and crystal orientation values of the drawn UHMWPE specimens increase only slightly, as their DR values increase from 20 to 40, wherein both crystallinity values of orthorhombic and monoclinic crystals increase slightly. In fact, barely any oriented kebab but only shish crystals were observed on the surfaces of drawn UHMWPE fiber specimens with DR values higher than 20. The birefringence values increase only slightly with further increasing DR values, while crystallinity and crystal orientation values of the drawn UHMWPE fiber specimens remained relatively unchanged as their DR values increase from 40 to 150. In the meantime, the monoclinic crystals gradually grow at the expense of the orthorhombic form crystals as the DR values of drawn UHMWPE fiber specimens increase from 40 to 150. Possible reasons accounting for these interesting properties found for the drawn UHMWPE fibers with varying draw ratios are proposed in this study.     

正交、菱面体和立方钙钛矿结构间的关系

通过对近年来正交、菱面体和立方三种对称类型钙钛矿锰氧化物实验结果的比较,研究了不同对称类型结构之间的关系,指出正交和菱面体结构偏离立方结构的幅度不大,所以在定性研究钙钛矿型锰氧化物某些物理问题时,可将三种对称类型统一用等效立方晶胞来表示。     

Mechanics of three-dimensional braided structures for composite materials – part I: fabric structure and fibre volume fraction

This paper is the first part of a series on the mechanics of three-dimensional braided structures for composite materials which include fabric structure and fibre volume fraction models, prediction of mechanical properties, finite element analysis and simulation of deformations. In the present paper, the normalized pitch length is introduced as a key parameter of three-dimensional braided structures. It is demonstrated that the braiding angles and fibre volume fractions can be represented as functions of this key parameter. The structures of three-dimensional braids were simulated and the braided fabrics and preforms were designed and produced. Fibre volume fraction models were established. The predictions from the fibre volume fraction models are supported by experimental results.     

Sc2W3O12/ZrO2可控热膨胀复合材料的制备

采用固相法成功制备了纯度较高的各向异性负热膨胀材料Sc₂W₃O₁₂。将ZrO₂与Sc₂W₃O₁₂按一定体积比混合, 在1200 ℃烧结10 h制备Sc₂W₃O₁₂/ZrO₂复合材料。通过XRD、SEM、EDS和热膨胀仪对合成样品的晶体结构、断面形貌和热膨胀性能进行表征。结果表明: 样品组元为正交相Sc₂W₃O₁₂和单斜相ZrO₂; 在 30~600 ℃内, Sc₂W₃O₁₂/ZrO₂复合材料的热膨胀系数皆线性一致, 并且通过改变Sc₂W₃O₁₂的体积分数, 其热膨胀系数可以控制为正、负或零, 其中60%Sc₂W₃O₁₂/ZrO₂复合材料在30~600 ℃的平均热膨胀系数为0.026×10^-6 ℃^-1, 近似为0。     

坡缕石/聚丙烯酸(钠)高吸水复合材料的溶胀行为

以水溶液聚合法制备了坡缕石/聚丙烯酸(钠) (PAANa)高吸水复合材料,对复合材料的吸水溶胀性能进行了研究,并采用FTIR对复合材料进行表征。结果表明：10 %坡缕石/PAANa复合材料吸蒸馏水和0.9 wt%盐水倍率分别达1666g/g、115g/g,较纯PAANa的724g/g、58g/g明显提高;坡缕石/PAANa复合材料具有优异的保水及反复吸水性能;坡缕石/PAANa的吸液倍率随电解质溶液离子强度的升高而降低,降低程度顺序为 Al3+>Ca2+>Na+;坡缕石/PAANa复合材料与其他6种矿物/PAANa复合材料相比,吸液性能特别是吸蒸馏水及0. 9 wt%盐水性能大幅提高。     

Enhanced photocatalytic of N/F-doped-NaTaO3 photocatalyst synthesized by hydrothermal method

N/F-doped NaTaO₃ powders were synthesized via a hydrothermal method at 160 °C. The influences of N/F co-doping on the crystal structure, morphology and photocatalytic properties of the NaTaO₃ powders were investigated systematically. Rietveld refinement of X-ray diffraction data confirm that the nanoparticles of pure NaTaO₃ have orthorhombic structures with Pc21n:bca and Ta₂O₅ can be obtained by doping N/F molar ratio (NaOH/NH₄F ≤ 1) with the orthorhombic P2 mm:cab space group. The NaTaO₃ powders are transformed from orthorhombic Pc21n:bca into monoclinic P2/m:b space group with the NaOH/NH₄F molar ratio (NaOH/NH₄F > 1). The well-defined cubic block NaTaO₃ single-crystalline particles with the size of 0.5 μm are determined using TEM and grow preferentially along (101) and (010) crystal planes. The photocatalytic activities were evaluated by the degradation of Rhodamine B under UV-light irradiation. The possible mechanism is proposed to discuss the enhanced photocatalytic activity based on the increasing separation efficiency of photoinduced charge. The results illustrate that the obtained monoclinic N/F-NaTaO₃ (NaOH/NH₄F = 1.5/1.0) powder exhibits the best photocatalytic activity with the UV-light irradiation for 210 min.     

Effects of Co and Fe addition on the properties of lanthanum strontium manganite

The effects of Co and Fe dopants with the amount of 20 and 40 mol% on the properties of La_0.84Sr_0.16MnO₃ were investigated. All compositions were prepared by conventional mixed oxide process and sintered at 1450 °C. The structure of undoped and Co-doped compositions was found to be monoclinic. In addition, the second phase was observed in these sintered compositions. The conductivity of doped materials decreased as compared to that of La_0.84Sr_0.16MnO₃. The SEM microstructure showed the decrease of grain size as Co content increased. The thermal expansion coefficient (TEC) tended to increase as Co content increased. In contrast, the monoclinic and orthorhombic structures were found in 20 and 40 mol% Fe-doped La_0.84Sr_0.16MnO₃. The amount of second phase in sintered composition depends on the amount of Fe content. The conductivity at 1000 °C decreased, but the grain size increased as Fe content increased. The thermal expansion coefficient slightly changed with Fe addition.     

纳米坡缕石润滑油添加剂对灰铸铁HT200摩擦磨损性能的影响

制备坡缕石纳米粒子添加到150N基础油的润滑油体系,在MMU-10G摩擦磨损试验机上分别对该纳米粒子润滑油体系和纯150N基础油,在混合润滑条件下的铸铁HT200试样对摩时的摩擦磨损性能进行研究,并用SEM和金相显微镜对磨损表面进行观察和分析,借助EDX测定试样表面成分的变化,探讨摩擦磨损性能变化的机理。结果表明:自制备的用KH550硅烷偶联剂球磨修饰的坡缕石纳米粒子在基础油中分散性良好,在该润滑剂润滑条件下对摩的试样表面生成了自修复膜层,其磨损量明显减小,失重量下降约25.2%,平均摩擦系数下降约32.3%。     

Structural and mechanical properties of sol–gel prepared pyrochlore lanthanum niobates

Lanthanum orthoniobate LaNbO₄ (LN) precursors were prepared by a modified polymeric complex sol–gel method using Nb-tartrate in different solvents (ethanol or methanol) with calcination at 750 °C. The monoclinic LaNbO₄ and orthorhombic LaNb₅O₁₄ phases were formed after annealing at 900 °C from precursors synthesized in ethanol (LN_et) and methanol (LN_met), respectively. FTIR and Raman spectra confirmed different structures of LN at 900 °C in both solvents. The microstructures indicate the strong effect of solvents on surface morphology. TEM and SAED patterns verified the monoclinic LaNbO₄ and orthorhombic LaNb₅O₁₄ phases with ferroelastic domains at 750 and 900 °C, respectively. Mechanical characterization was conducted for the first time by nanoindentation on the sol–gel derived LN after annealing at a low temperature. The hardness and elastic modulus of LN_met (LN_et) were measured to be ~2.6(1.5) and ~45(30) GPa, respectively. The modulus and hardness of LN_met were higher in comparison with LN_et. The strong solvent effect on mechanical properties of lanthanum niobate was confirmed.     

Proprietes physiques et structurales de la phase CrxV1−xO2

The Cr_xV_1−xO₂ solid solution has been studied by D.T.A., X-ray diffraction, magnetic susceptibility and electrical conductivity measurements. Three phases with related structures are made in evidence at any composition; they are respectively monoclinic, orthorhombic and tetragonal with the rutile structure. The extension of the homogeneity ranges with composition and temperature and the evolution of the conduction mechanisms are explained.