Effective charges in binary and ternary oxide compounds

Effective charges in non-cubic binary oxide crystals are evaluated on the basis of their transverse and longitudinal optical phonon frequencies. The temperature dependence of the effective charge is reported in quartz, rutile and corundum. Three procedures which allow the determination of effective charges in ternary compounds are presented and applied to halogenate, silicate, aluminate and ABO_n-type crystals, where A is an alkali or alkaline earth and B is a transition-metal element. Results are compared with Phillips's ionicities.     

Energies of tetranuclear transition-metal systems

The general problem of determining the relative energies of a system of four weakly-interacting transition-metal ions is considered when there is spin but no spatial degeneracy. Interaction hamiltonians that are quadratic and biquadratic in the spins are employed. The irreducible tensor method is used.     

Electron correlation and hybridization in late-transition-metal compounds

In this article we discuss the transition-metal d-d Coulomb interaction U and the anion-to-cation charge transfer energy jfor nickel halides and relate these to the observed bandgaps. In addition, we describe the degree of hybridization for NiCl 2 and NiBr 2 and transition-metal chlorides by considering the ionicity of the chemical bond of these compounds and the results obtained with the Phillips-Van Vechten dielectric theory. The degree of hybridization in transition-metal chlorides has been obtained by considering a simple model which utilizes the photon energy dependence of the photoionization cross-sections for the 3p band of the chlorine ions and the 3d band of the transition-metal ions. Good agreement between the two approaches has been found and a degree of hybridization between 0.15 and 0.25 for transition-metal chlorides is confirmed.     

A pulsed EPR method to determine distances between paramagnetic centers with strong spectral anisotropy and radicals: The dead-time free RIDME sequence

Methods to determine distances between paramagnetic metal centers and radicals are scarce. This is unfortunate because paramagnetic metal centers are frequent in biological systems and so far have not been employed much as distance markers. Successful pulse sequences that directly target the dipolar interactions cannot be applied to paramagnetic metal centers with fast relaxation rates and large g-anisotropy, if no echos can be detected and the excitation bandwidth is not sufficient to cover a sufficiently large part of the spectrum. The RIDME method Kulik et al. (2002) [20] circumvents this problem by making use of the T₁-induced spin-flip of the transition-metal ion. Designed to measure distance between such a fast relaxing metal center and a radical, it suffers from a dead time problem. We show that this is severe because the anisotropy of the metal center broadens the dipolar curves, which therefore, only can be analyzed if the full curve is known. Here, we introduce five-pulse RIDME (5p-RIDME) that is intrinsically dead-time free. Proper functioning of the sequence is demonstrated on a nitroxide biradical. The distance between a low-spin Fe(III) center and a spin label in spin-labeled cytochrome f shows the complete dipolar trace of a transition-metal ion center and a spin label, yielding the distance expected from the structure.     

Vapor-liquid (insulator-metal) phase transition in alkali metal vapors

A simple physical model is proposed that describes a vapor-liquid phase transition in alkali metal vapors. The model is based on an assumption made on the character of binding between atoms in the gas phase near the critical point. This is the collective quantum cohesive energy, well-known in the theory of liquid alkali metals, which arises due to the appearance of conduction electrons and is extended to the gas region near the critical point. The parameters of the critical points of the transition and of the binodal are determined on the basis of the model calculation of the binding energy for all alkali metals. Combined, these parameters well agree with experimental results and the predictions made by other authors. The minimum metallic conductivity is evaluated. Its behavior allows one to conclude that vapor-liquid and insulator-metal transitions in alkali metal vapors coincide. This fact sheds light on the Zel’dovich-Landau problem as applied to alkali metal vapors.     

Arsenic toxicity: an atom counting and electrophilicity-based protocol

The atomic number (Z) and electrophilicity index (ω) have been utilized to explain the toxicity of various alkali and transition-metal ions as well as to predict that of the arsenic ions. The toxicity of two different training sets of arsenic derivatives is described using the global electrophilicity (ω) and number of nonhydrogenic atoms (N _NH) along with the local philicity (w_As⁺){(\omega _{\rm As}^+)} and the atomic charge (Q _As) on the arsenic atom. Applying the regression models from the training sets, toxicity of some unknown arsenic derivatives is predicted.     

Orbital polarization in itinerant magnets

We propose a parameter-free scheme of calculation of the orbital polarization (OP) in metals, which starts with the strong-coupling limit for the screened Coulomb interactions in the random-phase approximation (RPA). For itinerant magnets, RPA can be further improved by restoring the spin polarization of the local-spin-density approximation through the local-field corrections. The OP is then computed as the self-energy correction in the static GW method, which systematically improves the orbital magnetization and the magnetic anisotropy energies in transition-metal and actinide compounds.     

一维体系的电声子相互作用和声子激发

通过一维金属卤素络合物模型和一维分子晶体模型研究了一维体系的电声子相互作用和声子激发．给出了在绝热近似下重整化的声子色散关系．结果表明：（１）两个模型中电声子相互作用不同，导致前者声频声子重整化可略而后者重整化修正明显；（２）与高分子材料的Ｓｕ-Ｓｃｈｒｉｅｆｅｒ-Ｈｅｅｇｅｒ模型不同，两个模型的声子谱均无能隙 关键词：     

基于XRD与FTIR的碱钢渣胶凝材料复合激发机理研究

以Na₂SiO₃、NaOH和Ca(OH)₂制备碱溶液,然后利用碱溶液对钢渣进行活化处理。分别研究Na₂SiO₃用量、NaOH用量和Ca(OH)₂用量对碱钢渣胶凝材料的力学性能影响,获得最优力学性能的碱钢渣胶凝材料。采用XRD,FTIR和SEM对最优力学性能的碱钢渣胶凝材料进行表征。结果表明,当NaOH用量为4.50 g、Na₂SiO₃用量为11.25 g和Ca(OH)₂用量为6.75 g时,碱钢渣胶凝材料的力学性能最优。Na₂SiO₃对碱钢渣胶凝材料的7 d抗压强度影响显著,NaOH对碱钢渣胶凝材料的3 d抗压强度影响显著,Ca(OH)₂对碱钢渣胶凝材料的28 d抗压强度影响显著。Na₂SiO₃,NaOH和Ca(OH)₂碱性物质的加入促使钢渣形成稳定的C-S-H凝胶与沸石类相。     

A closer look at photochemical reactions of transition-metal compounds by time-resolved EPR

A review is given of applications of time-resolved electron paramagnetic resonance (TREPR) in the field of photochemistry of transition-metal compounds. The two main TREPR techniques used in these studies are described. A brief overview is given of chemically induced dynamic electron polarization mechanisms that can affect TREPR spectra and that can give insights into the mechanism of photochemical reactions. Following these background sections, experimental results are presented. The discussion focuses in particular on the Fourier-transform EPR studies of photoinduced metal-alkyl bond homolysis reactions of a series of transition-metal (Co, Ru, Re, Pt) complexes carried out by the authors.     

双光子吸收碱金属蒸气激光器研究进展

蓝紫激光和中红外激光在基础研究和国防工程中有重要的应用前景。单光子吸收的碱金属蒸气激光器具有量子效率高、受激发射截面大和热管理性能好等优点,近些年来已成为激光领域中研究热点之一,目前已实现k W量级的输出。双光子吸收的碱金属蒸气激光器可实现蓝紫激光和中红外激光级联输出的特性,也引起越来越多的关注。本文从碱金属原子密度、泵浦光功率、偏振和频率失调量以及调控激光等几种影响因素出发,综述了双光子吸收碱金属蒸气激光的研究进展,在此基础上分析了影响激光输出特性的原因,最后对双光子吸收碱金属蒸气激光器的发展趋势进行了展望。     

Density-functional investigation of 3d,4d,5d impurity doped Au6 clusters

The general features of the geometries and electronic properties for 3d,4d,and 5d transition-metal atom doped Au 6 clusters are systematically investigated by using relativistic all-electron density functional theory in the generalized gradient approximation(GGA).A number of structural isomers are considered to search the lowest-energy structures of M@Au 6 clusters(M=3d,4d and 5d transition-metal atoms),and the transition metal atom locating in the centre of an Au 6 ring is found to be in the ground state for all the M@Au 6 clusters.All doped clusters,expect for Pd@Au 6,show large relative binding energies compared with a pure Au 7 cluster,indicating that doping by 3d,4d,5d transition-metal atoms could stabilize the Au 6 ring and promote the formation of a new binary alloy cluster.     

Photoemission and scanning tunneling experiments with small particles on solid surfaces

The fascination of research with nanometersized objects in contact with a macroscopic surface will be illustrated by two examples: mass-selected supported transition-metal clusters and C₆₀ molecules on metallic single-crystal substrates. The preparation, mass-selection and deposition of the small particles will be described in some detail. The main experimental techniques involved in the characterization of their electronic and structural properties are photoelectron spectroscopy and scanning tunneling methods. For the transition-metal clusters the evolution of the valence band with cluster size reveals a trend to metal formation. When the tip of a Scanning Tunneling Microscope (STM) is placed above individual C₆₀ molecules intense light emission is observed. The diameter of this emission spot is approximately 4 Å. This observation indicates the possibility of an optical spectroscopic analysis on the scale of individual molecules.     

小米米粉碱消值的高光谱快速预测

小米米粉的主要成分是淀粉,其食味品质决定小米米粉的市场价值。糊化特性是小米米粉的重要物理特性,而碱消值是能够直接反应其糊化特性的主要特征指标。通过小米米粉碱消值的差异,可以间接反映直链淀粉含量,当碱消值降低时,相反,糊化温度和直链淀粉含量却很高,而小米米粉口感粘糯性越差。采用高光谱技术结合化学计量学方法,建立快速检测小米米粉碱消值预测模型,旨在探索一种快速、无损、低成本预测小米米粉碱消值的方法。实验采集小米米粉高光谱数据,在被测样品感兴趣区域(ROI)按像素点逐一选择,提取高光谱数据矩阵,并进行均值运算,得到每个样品在各个光谱波段的平均光谱值。利用粘度测定仪(RVA)测定小米米粉碱消值指标。光谱数据采用全波段、竞争性自适应重加权采样法(CARS)及随机蛙跳(RF)法选择特征波段处理,建立偏最小二乘回归(PLSR)模型;全波段建立预测模型R_p值最高为0.77,说明能够利用小米米粉高光谱反射率反演小米米粉的碱消值,而采用其他两种计算方法所得R_p值分别为0.72和0.7,与前者较为接近,也反映了采用CARS和RF建立的回归模型具有可行性。为提高预测精度,采用Savitzky-Golay(S-G)法、多元散射校正(MSC)和S-G+MSC对数据预处理。可以看出采用MSC预处理光谱数据建立PLSR模型性能较好(R_p=0.83)。对MSC预处理后的数据再次CARS和RF法选择特征波段,建立PLSR模型,与未进行预处理的回归模型相比,R_p值变化不大,这也说明CARS和RF具有一定的稳定性,可以作为小米米粉高光谱反射率预测碱消值的参考方法。结果表明：为实现对小米米粉碱消值的快速、无损检测,通过运用高光谱技术能够利用小米米粉高光谱反射率预测碱消值,进而为小米米粉品质评级、加工及碱消值传感器的开发提供参考依据和数据支撑。     

Mössbauer spectroscopic study on portland cement clinker containing alkali ions

The clinker raw mixture (84 wt % limestone + 12 wt % clay +4 wt% pyrite ash) was divided into five portions. Each portion was mixed with an alkali carbonate and fired at a certain temperature along half an hour then quenched in air. A portion was left without alkali and fired at 1450°C to investigate the effect of alkali addition. Each portion was ground and refired at a temperature less than the first firing by about 100°C for ten hours to ensure that the cliniker had been fully formed, then quenched in air. Each clinker was measured by Mössbauer spectrometer and x-ray diffractometer. Each clinker was mixed with 5 wt% natural gypsum then with 25 wt% water. The compressive stength test was performed at three days of hydration. The results were compared with the results of ordinary Portland cement.     

碱液修饰对硅纳米线阵列电池光谱响应的影响

采用金属催化化学腐蚀法在p型(100)硅基底上制备了硅纳米阵列,然后用碱溶液对纳米线阵列进行修饰。分别研究了碱液修饰对硅纳米线阵列形貌、光电性质的影响。研究表明: 与绒面及纳米线阵列相比,碱修饰30 s硅纳米线阵列的表面分散均匀,反射率降低;光谱响应度显著提高,并且出现最大量子效率对应波长红移现象。最后,详细讨论了碱液修饰硅纳米线阵列电池对光谱响应的影响机制。     

Interionic potentials in alkali halides and their use in simulations of the molten salts

After an outline of work on rare-gas systems, which serves as a target for parallel work on alkali halides, and an initial brief survey of those parts of this parallel work for which results have been obtained, interionic potential models for alkali halides are considered in some detail. The rigid ion potentials of Fumi and Tosi are discussed and then a major part of the section is devoted to deriving a new set of polarizable ion potentials, which incorporate the ideas behind the lattice dynamical shell model. Extensions which include many-body terms in the potentials are considered briefly and finally the information which can be obtained from alkali halide diatomic molecules is discussed.

In the third section methods of computer simulation for ionic liquids are outlined, concentrating on the molecular dynamics method, and some of the properties which can be obtained by analysing the ion trajectories are listed. Results from simulations, including some new work on LiF, NaCl and RbI, are reviewed.     

First-principles calculations of the monoclinic transition-metal doped NaMnO2 cathode material

ABSTRACT

Using spin-polarised generalised gradient approximation (GGA?+?U), I successfully investigate the electronic properties of the monoclinic NaMnO₂ doped with Cr, Fe and V atom to enhance the electrochemical performance. The expansion of volumes is induced by the dopants. The lowest conduction band and highest valence band are mostly from d orbital of Mn atom and transition-metal dopants which are responsible for the electronic conductivity. Na(Mn, Fe)O₂ is a semiconductor with the reduced band gap. Cr and V doping in NaMnO₂ compound reveal the half-metallic performance. The enhancement of the insertion potentials is induced by transition-metal dopants. The electronic conductivity of NaMnO₂ cathode material is improved by Cr-doping scheme. Finally, this research presents the new horizons for the expenditure of transition-metal doping for designing and improving the NaMnO₂ cathode materials in Na-ion rechargeable batteries.     

Electronic theory of the chemisorption effect on surface segregation in transition-metal alloys

The tight-binding Ising model generalized for a system consisting of a transition-metal alloy with chemisorbed adatoms is used to calculate the effect of hydrogen chemisorption on surface segregation in a Cu---Ni alloy. The simple model of chemisorption and of the band structure of the alloy is assumed. The charge-neutrality condition is incorporated into the model.     

A model for alkali chemisorption

The linear response function in the density functional formalism, developed by Ying, Smith and Kohn, is applied to alkali chemisorption on metallic surfaces. The adion is represented by a pseudopotential perturbing the surface. Binding energies, induced dipole moments, and vibrational frequencies at the equilibrium position are first calculated for the alkalis at finite coverage, as well as, in the limit of zero coverage, on a jellium substrate. The theoretical results are in good agreement with available experimental results. The effect of electric fields on chemisorbed alkali ions is discussed with reference to interpretation of experimental results. The crystalline structure is then introduced in the form of a periodic pseudocharge density representing the ionic lattice. In this model, corrections to the quantities calculated in the jellium approximation are obtained for both low index and high index planes. Preferred adsorption sites are determined and found to be consistent with experimental findings.