Structural parameters and IR spectra of spinel solid solutions (MV2O4)c(MgFe2O4)1−c(M ≡ Co,Fe)

An x-ray method and the method of cluster components are used to find the distribution of cations over the lattice points of crystals of the solid solutions (CoV₂O₄)_c(MgFe₂O₄)_1–c and (FeV₂O₄)_c(MgFe₂O₄)_1–c with spinel structure. A method of selecting the properties of the solutions which may be Interpreted by the method of cluster components is proposed and it is shown that this method describes the concentration dependences of the lattice parameters, oxygen parameters, and frequencies of the absorption spectra of the investigated solutions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 16–21, April, 1976.     

Synthesis of Ni1−xZnxO hollow structures by a facile method

By a sol–gel method, we obtained Ni_1−xZn_xO polycrystalline powders. The obtained Ni_1−xZn_xO was characterized by scanning electron microscope and transmission electron microscope techniques. The characterized results showed that the obtained Ni_1−xZn_xO showed hollow structure. The grain sizes of the obtained hollow Ni_1−xZn_xO were quite uniform, typically in the range of 400–500 nm. This method is a simple and effective method for large-scale synthesis of hollow Ni_1−xZn_xO quasi-spheres. The present method is very promising for large-scale production because the method is only involves commercial Zn(AC)₂·2H₂O and NiCl₂·6H₂O powders and the reaction is achieved in an open system free of autoclave and organic chemical reagents. This template-free method is facile but effective and therefore it is very promising for large-scale industrial production.     

The magnetic entropy change in La0.8Ce0.2Fe11.4Si1.6Bx compounds prepared by copper-mold casting

The magnetocaloric effect (MCE) of La_0.8Ce_0.2Fe_11.4Si_1.6B_x (x=0.0-0.5) compounds, prepared by a copper-mold casting (CMC) method, has been investigated. Comparing with the conventional arc-melting (CAM) method, the relatively homogenous composition and microstructure were achieved in the precursor alloys prepared by the CMC method. As a result, the annealing time is dramatically shortened from several weeks for CAM alloys to 2 h for CMC alloys, suggesting that CMC method is a time-saving and energy-saving method for fabrication of MCE alloys. On the other hand, it is revealed that B addition gives rise to an enhancement of Curie temperature (T_C), a reduction of thermal lag and magnetic hysteresis and a broadening of working temperature span as well. Although the peak value of magnetic entropy change decreases with B content, various B-contained compounds hold close refrigerant capacities. Comprehensively considering magnetocaloric properties of the B-contained La_0.8Ce_0.2Fe_11.4Si_1.6B_x compounds, it can be concluded that the B-contained compounds prepared by CMC method are promising candidates of magnetocaloric materials in practical application.     

属特殊结构系列的若干碳化硅多型体的晶体结构

碳化硅(SiC)是典型的层状结构化合物。到目前为止,已发现了150种以上的多型体。作者曾发展了一种特殊的劳厄法可有效地鉴定碳化硅多型体。这种方法,我们发现了85种碳化硅新多型体。为了测定其中一些多型体的结构,拍摄了回摆和魏森堡照相作结构分析,但没有成功。因为这些照相中只有一些基本类型6H,15R和8H的衍射斑点而没有高层多型体的斑点,这是由于新多型体在晶体中含量很少且这些薄晶体多型体处于基本类型6H,8H,15R中间的缘故。本文提出了一种测定碳化硅多型体晶体结构的劳厄法。提出了计算劳厄斑点衍射强度的方法。对结构系列[(33)_m32]₃,[(33)_m34]₃,[(22)_m23]₃和[(44)_m43]₃多型体的结构因子F_hkl的计算方法作了简化。利用这种方法对9种碳化硅新多型体的晶体结构作了测定,其结构用z字形堆垛(Жданов符号)表示时为231R:[(33)₁₂32]₃,249R:[(33)₁₃32]₃,321R:[(33)₁₇32]₃, 339R:[(33)₁₈32]₃,237R:[(33)₁₂34]₃,417R:[(33)₂₂34]₃, 453R:[(33)₂₄34]₃,93R:[(44)₃43]₃,261R:[(44)₁₀43]₃。 关键词：     

EPMA mapping method for small particles of Al3Fe,Al6Fe, α‐AlFeSi and β‐AlFeSi in 1050‐H18 aluminum sheets

We developed an EPMA mapping method for small Al_aFe_bSi_c particles in 1050‐H18 aluminum sheet, which is one of the base materials coated by photoresist in advance called PS plate (pre‐sensitized printing plate). In this method, we used the ratios of relative x‐ray intensities, I_Fe/I_Al and I_Fe/I_Si instead of the mass ratios, Fe/Al and Fe/Si, of the main elements which constitute the particles and tried to determine the ratios of relative x‐ray intensities using Monte Carlo calculations. Furthermore, using this developed mapping method, we performed the mapping of small Al_aFe_bSi_c particles such as Al₃Fe (0–3%Si as impurities), Al₆Fe (0–1%Si as impurities), α‐AlFeSi(Al_8.3Fe₂Si) and β‐AlFeSi(Al_8.9Fe₂Si₂) in 1050‐H18 aluminum sheets. We found that the discrimination of these particles was achieved with this mapping method. We confirmed that this method is useful for the mapping of Al_aFe_bSi_c particles in 1050‐H18 aluminum sheets. Copyright © 2004 John Wiley & Sons, Ltd.     

Channel-combination method for phase-based |B1+| mapping techniques

PurposeThe aim of this study was to propose a channel combination method for |B₁⁺| mapping methods using phase difference to reconstruct |B₁⁺| map.Theory and methodsPhase-based |B₁⁺| mapping methods commonly consider the phase difference of two scans to measure |B₁⁺|. Multiple receiver coils acquire a number of images and the phase difference at each channel is theoretically the same in the absence of noise. Affected by noise, phase difference is approximately governed by Gaussian distribution. Considering data from all channels as samples, estimation can be achieved by maximum likelihood method. With this method, all phase differences at each channel are combined into one. In this study, the proposed method is applied with Bloch-Siegert shift |B₁⁺| mapping method. Simulations are performed to illustrate the phase difference distribution and demonstrate the feasibility and facility of the proposed method. Phantom and vivo experiments are carried out at 1.5 T scanner equipped with 8-channel receiver coil. In all experiments, the proposed method is compared with weighted averaging (WA) method.ResultsSimulations revealed appropriateness of approximating the distribution of phase difference to Gaussian distribution. Compared with WA method, the proposed method reduces errors of |B₁⁺| calculation. Phantom and vivo experiments provide further validation.ConclusionConsidering phase noise distribution, the proposed method achieves channel combination by finding the estimation from data acquired by multiple receivers coil. The proposed method reduces |B₁⁺| reconstruction errors caused by noise.     

Tl2Ba2Ca2Cu3Oy超导体磁通钉扎能的分布

描述一种测量高温超导体磁通钉扎能U₀及其分布的新方法,此方法主要之点是测量磁化后样品的零场临界电流随时间的变化,利用这一方法测量Tl₂Ba₂Ca₂Cu₃O_y的U₀值分布(T=78K)。根据所得结果,对已报道的U₀值的分散性提出一种新解释。 关键词：     

Vector analysis vs. regions of integration ratio method for determination of gamma and neutron contributions in a mixed field

The different ratios of the dosimetry peaks and the high temperature peaks after gamma and neutron irradiation can be employed for mixed field dosimetry, after performing proper analysis. In the present work the results obtained by the vector analysis method were compared to those obtained by the regions of integration (ROI) method for TLD600 chips irradiated by different combinations of gamma rays and thermal neutron doses. When applying the ROI method, the calculated neutron to gamma dose ratios (D_n/D_γ) were in good agreement (differences up to about 20%) with the actual experimental values in the D_n/D_γ range from 0.033 to 20. When applying the vector analysis method, the range of the D_n/D_γ ratio with differences up to about 20% is reduced to 0.033–4, and the uncertainties are generally higher. Thus, no advantage is expected when using the vector analysis method compared to the ROI method for evaluation of the dose ratio D_n/D_γ in a mixed field.     

Cobalt-containing oxide layers on titanium, their composition, morphology, and catalytic activity in CO oxidation

In this study possibility to form the layered compositions CoO_x + SiO₂/TiO₂/Ti by plasma electrolytic oxidation (PEO) method was shown. Compositions have been obtained by both one-stage PEO method (Method I) with addition of Co(CH₃COO)₂ into silicate electrolyte and impregnation of preliminary obtained by the PEO method SiO₂/TiO₂/Ti systems in aqueous solutions containing cobalt salts with their following annealing (Method II). XRD, XPS and SEM/EDX were used to investigate the phase and element composition, microstructure of the coatings prepared by the two various methods. Catalytic activity of the cobalt-containing composites was investigated in the CO oxidation reaction. Under experimental conditions, the structures obtained by impregnation and annealing method were more active, than those obtained by one-stage PEO method. The surface structures of cobalt-containing coatings obtained by the PEO method and by impregnation and annealing differ in both quantitative and qualitative relation. The cobalt content on the surface of impregnating coatings is three times as much as that for those formed by one-stage PEO method. It is found that coatings obtained by the Method II have a more developed surface. The surface of CoO_x + SiO₂/TiO₂/Ti compositions obtained by the PEO method contains, presumably Co(OH)₂ and Co₃O₄. The surface of the similar compositions obtained by the Method II, possibly contains CoO, either Co₂O₃, or CoOOH. The combination of these factors, perhaps, also provides a higher activity of the compositions formed by the Method II.     

Regression analysis for deflection magnetic field parameters measured by the dual-coil method

In this study, the magnetic field-parameters of a typical saddle-shaped deflection yoke were measured using the dual-coil method developed by the group. The measurement data was processed and analyzed using two methods: 2-variable regression analysis method and 3-variable regression analysis method. The two results were compared with the analytically calculated results, which was used as the reference. It was shown that the data collection range has large impact to the results of H₂, H₄, and the further away from the central axis the probe is placed, the larger the error is. The errors of H₂ and H₄ are smaller using the 3-variable regression analysis method as compared with the ones using 2-variable regression method. The 3-variable regression analysis method uses H₆ in the process of calculating H₂ and H₄, which is coincident with the definition of them in the formula of H_y = H₀ + H₂X² + H₄X⁴ + H₆X⁶ +?.     

Tb0.3Dy0.7Fe2合金的本构参数辨识方法研究

建立了一种简便的、适用于磁畴模型应用的Tb_0.3Dy_0.7Fe₂ 合金本构参数辨识方法. 针对Tb_0.3Dy_0.7Fe₂合金磁畴模型中本构参数不明确且直接实验测试困难的问题, 提出了一种数值计算与实验测试相结合的参数辨识方法. 采用坐标变换与绘制自由能等势曲线相结合的方法, 简化了载荷作用下Tb_0.3Dy_0.7Fe₂ 合金内磁畴角度偏转的数值计算, 研究了合金磁畴角度偏转模型的参数依赖性. 在此基础上, 结合简单的实验测试, 建立了Tb_0.3Dy_0.7Fe₂合金各向异性常数K₁ 和K₂、能量分布因子ω、晶轴取向分布的辨识及修正方法. 该方法能够简单、快速地完成Tb_0.3Dy_0.7Fe₂ 合金磁畴模型中本构参数的辨识, 对完善磁致伸缩材料磁畴偏转的数值计算模型非常有意义. 理论分析可为类磁致伸缩材料磁机耦合模型的建立、完善, 以及材料本构参数的辨识、获取提供参考.     

结合除谱,差谱,二阶差谱的二氯化铜水溶液中直接接触离子对的紫外可见吸收光谱研究

The microstructure of aqueous CuCl₂ has been studied through lots of technologies for many years; however, it remains a controversial subject. In this study, a new spectroscopic method has been proposed to analyze the UV-visible spectra of thin film of CuCl₂/H₂O solutions at different concentrations. This method is the combination of ratio spectra, difference spectra and second order difference spectra. By using this method, two new bands at ~230 and ~380 nm are obviously observed. The bands are assigned as the contacted ion pairs[CuCl₃(H₂O)_n]^- or[CuCl₄(H₂O)_n]^2-, which demonstrates that ion pairs exist in the CuCl₂/H₂O solution. Such finding agrees with the recent theoretical spectra obtained by time-dependent density functional theory. Furthermore, the populations of the contacted ion pairs are discussed. This study not only offers the direct spectroscopic evidence of[CuCl₃(H₂O)_n]^- or[CuCl₄(H₂O)_n]^2- in aqueous CuCl₂, but also suggests that the spectroscopic analysis method is powerful to extract the weak bands in a strong overlapping spectrum.     

Study of chemical shift in Ll and Lƞ X‐ray emission lines in different chemical forms of 48Cd and 50Sn compounds using WDXRF technique

Chemical shift in Ll and L? X‐ray emission lines of ₄₈Cd and ₅₀Sn elements in various chemical compounds was determined with high resolution wavelength dispersive X‐ray fluorescence (WDXRF) spectrometer. The positive and negative shifts were measured in ₄₈Cd compounds viz, CdS, CdB₄O₇, CdCl₂, Cd₃(PO₄)₂, CdCO₃, CdI₂ and CdO with reference to pure Cd foil and ₅₀Sn compounds viz, Sn(CrO₄)₂, SnO, SnO₂, SnCl₂, SnF₂, SnF₄ with reference to pure Sn foil. The measured energy shifts in Ll X‐ray emission lines range from ?0.47 to 1.82 eV and L? emission lines range from ?2.67 to 1 eV for both compounds. The effective charges (q, q ^/ , q ^// , and q ^/// ) were calculated from four models (Pauling method, Suchet method, Levine method and Batsonav method) and found to be linear dependence with chemical shift. The measured chemical shifts were correlated with effective charge, number of ligands and electronegativity of the central metal atom in the given compounds.     

Controlling the composition and the magnetic properties of hexagonal Co2Z ferrite powders synthesized using two different methods

Polycrystalline Co₂Z hexaferrite (Ba₃Co₂Fe₂₄O₄₁) powders have been prepared via two wet chemical routes: sol gel auto-combustion (SGA) and co-precipitation (CP) methods. The effects of synthesis conditions on the crystal structure, crystallite size, morphology, and magnetic properties were systematically studied. The results revealed that single Co₂Z hexaferrite phase was obtained at relatively low temperature 1250 ^°C for 5 h via the SGA method whereas it was formed at 1300 ^°C for 6 h using the CP pathway. The microstructures of the pure powders appeared as a hexagonal platelet-like structure. The particle size of the pure Co₂Z powders by CP method was higher than as obtained by the SGA method. The soft characteristic loops were obtained for single Co₂Z hexaferrite phase synthesized using both routes. High saturation magnetization (M _s =53.7 emu/g) was achieved for the Co₂Z powder synthesized via the CP method compared with the formed single phase synthesized via the SGA method (M _s =47.0 emu/g). Good dielectric and dynamic magnetic properties were obtained for the Co₂Z powder synthesized via the SGA method in comparison with the sample synthesized via CP method. The results obtained are discussed on the basis of electromagnetic theory.     

Exsolution of Nickel Nanoparticles from Mixed-Valence Metal Oxides: A Quantitative Evaluation by Magnetic Measurements

A fast and accurate experimental method is demonstrated to assess the fraction of exsolved metallic nanoparticles using magnetic measurements. As a benchmark, nanometric metallic nickel exsolved from (La_1−xSr_x)(Cr_1−yNi_y)O_3−δ is used for its high relevance as a solid oxide fuel cell component. The method is based on the difference in the magnetic response of the exsolved metallic nickel (ferromagnetic) and Sr-doped lanthanum chromite ceramic matrix (paramagnetic). The exsolved nickel results in coherent nanoparticles pinned on the surface of the Sr-doped lanthanum chromite ceramic matrix, as evidenced by electron microscopy analyses. The results obtained indicate the procedure as a fast and sensitive method to study the exsolution of ferromagnetic nanoparticles.     

Conductivity and sintering property of LaNi1 − xFexO3 ceramics prepared by Pechini method

Preparation of LaNi_1 − xFe_xO₃, which is one of the candidate materials of solid oxide fuel cell cathode, current collecting layer and interconnect coating was examined with Pechini method and solid state reaction method. Single phase LaNi_1 − xFe_xO₃ with large Ni content has successfully been prepared by low temperature sintering as 750 °C with Pechini method, whereas large amount of raw materials has remained with solid state reaction method by sintering at the same temperature. It can be ascribed to more homogenous cation distribution in raw powder material prior to sintering with Pechini method. It has also been revealed that LaNi_1 − xFe_xO₃ with x lower than 0.3 is thermodynamically unstable in air above 1000 °C. LaNi_0.6Fe_0.4O₃ showed superior property as cathode material with high electrical conductivity, thermodynamic stability and appropriate sintering property.     

Estimation of the ionization potential for polyhalogenated hydrocarbons by weakest bound potential method

The weakest bound potential method was proposed to estimate the ionization potential (IP) of polyhalogenated methanes, that is, the model IP = aχ_ve + bPEI_fi + c was developed, in which χ_ve is molecular electronegativity calculated by valence electrons equilibration method, and polarizability effect index (PEI)_fi is the influence of polarizability effect. The result indicates that the model is reasonable and effective to predict the IP for polyhalogenated methanes. Besides, the quantum chemistry method, the MOPAC AM1 method, and the density functional theory (B3LYP) method were employed to calculate the IP values of the same polyhalogenated methanes, and those results were less than that of the weakest bound potential method. Furthermore, the experimental values of 67 polyhalogenated hydrocarbons were correlated with the parameters χ_ve and PEI_fi. The regression results show a good correlation (R = 0.988), and the average absolute error between the experimental values and the calculated values is only 0.10 eV. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of reaction temperature on morphology and electrochemical behavior

LiCoO₂ and LiMn₂O₄ compounds were synthesized using two different methods, viz., low-temperature-aided hydrothermal and high-temperature-assisted co-precipitation method. Keeping the reaction parameters such as type of precursors chosen and the medium of reaction as same for both the hydrothermal and co-precipitation methods, the effect of temperature in producing LiCoO₂ and LiMn₂O₄ with varying physical as well as electrochemical properties has been studied. As expected, the effect of low-temperature-involved hydrothermal method rendered finer particles of nanocrystalline nature with minimum strain, and the high-temperature synthesis of co-precipitation method produced slightly enhanced particle size with an increased strain value. The effect of size-grown particles resulting from co-precipitation method exhibited inferior electrochemical properties such as increasing resistance of the cell upon cycling and a significant decline in capacity behavior, irrespective of LiCoO₂ or LiMn₂O₄ cathodes. On the other hand, hydrothermal synthesis of LiCoO₂ and LiMn₂O₄ has exhibited acceptable specific capacity with an admissible capacity fade behavior and negligible internal resistance of the cell, thus qualifying the same as better-performing cathodes. Hence, the effect of low temperature in producing LiCoO₂ and LiMn₂O₄ cathodes with facile intercalation and de-intercalation of lithium is demonstrated.     

Preparation and luminescence of (SBA-15)–Eu2O3 composite materials

In this study, (SBA-15)–Eu₂O₃ host-guest composites have been prepared with SBA-15 mesoporous sieve as host and Eu₂O₃ as guest via the solid-phase ultrasonic method and liquid-phase medium ultrasonic method. The host–guest composite materials showed the properties of luminescence. Four excitation peaks appeared in the excitation spectra of the samples. The excitation peaks are located at 397, 415, 466, 537 nm; 392, 408, 464, 532 nm and 393, 406, 465, 533 nm for the nano-Eu₂O₃, the liquid-phase medium ultrasonic method (LPMUM) and the solid-phase ultrasonic method (SPUM) samples, respectively. SBA-15 has the well-ordered hexagonal arrays of mesopores, which makes centrosymmetry of Eu³⁺ higher in the prepared (SBA-15)–Eu₂O₃ samples. The intensity of ⁵D₀→⁷F₁ transition strengthens, and the intensity of ⁵D₀→⁷F₂ transition weakens.     

Calculation of electrostatic fields in ionic crystals based upon the Ewald method

Formulas for the electrostatic potential, field strength and field gradient due to monopoles, dipoles and quadrupoles are given, based upon the Ewald summation method. A convenient choice of the convergence parameter in the Ewald method is demonstrated in some actual calculations. A method to calculate self-consistent electrostatic fields due to self induced dipoles is evaluated. Monopole and self-consistent fields are calculated in Pb₂O₃, βMn₂O₃, FeTiO₃, MnF₃ and Pb₃O₄. The influence of the anion parameter on the electrostatic field is investigated for idealized CdCl₂ and TiO₂. Results of Madelung and induced dipole polarization energy for a series of arbitrary compounds are given. The effect of spontaneous polarization in polar crystals is discussed.