无压烧结制备透辉石/AlTiB增韧补强氧化铝基结构陶瓷材料

采用温度梯度无压烧结工艺制备了透辉石/AlTiB增韧补强Al2O3基结构陶瓷材料,探讨了其致密化烧结特性,并对其力学性能进行了测试和分析.研究了透辉石/AlTiB增韧补强Al2O3基结构陶瓷材料的微观结构,并分析了其力学性能和微观结构与透辉石含量的关系.结果表明:与纯Al2O3相比,透辉石/AlTiB增韧补强Al2O3基结构陶瓷材料的力学性能得到明显提高,其中添加6;(体积百分含量,下同)透辉石和4;AlTiB的Al2O3基结构陶瓷材料获得较好的综合力学性能,其硬度、抗弯强度和断裂韧性分别达到16.02 GPa、370 MPa和5.11 MPa·m1/2.力学性能提高的主要原因为:添加相与Al2O3基体之间界面反应的发生以及透辉石和AlTiB对复合材料的协同晶粒细化效应.     

Relationship Between Structure and Properties for Donor-Doped and for Acceptor-Doped Polyacetylene

Two basic structural types are experimentally derived for polyacetylene complexes: channel structures (Na, K, Rb, and Cs) and layered structures (iodine and a variety of other acceptors). Observed variants for the layered structures include first-stage and higher-stage complexes, with either complete or fractional occupation of dopant on the dopant-containing planes. A third structural type, in which dopant is statistically distributed, is predicted up to high dopant levels for lithium dopant. These structural results are used to explain observed properties and to predict properties obtainable for nearly defect-free single crystals. Discussions will include the structural origin of electrochemical discharge curves, major increases in conductivity on annealing K-doped and Rb-doped polyacetylene, the extremely high thermal stability of alkali metal channel complexes, and predicted mechanicals and transport properties for single-crystal complexes.     

Liquid properties of Pd-Ni alloys

Liquid properties of Pd-Ni metal alloys are computed by molecular dynamics (MD) simulation with the use of quantum Sutton-Chen potential (Q-SC) model. The thermodynamical, structural, and transport properties of the alloy are investigated. The melting temperatures for Pd-Ni system are predicted. The temperature and concentration dependence of diffusion coefficient and viscosity are reported. The transferability of the potential is tested by simulating the liquid state. The values of melting point are in excellent agreement with the experiment. Comparison of calculated structural and dynamical properties with the available experiments and other calculations shows satisfactory consistency.     

Growth of ZnO bulk crystals: A review

A critical review is proposed of the different techniques of bulk growth of ZnO crystals for their use as a substrate in the homoepitaxial growth of this attractive compound. The crystals are assessed from their structural and electrical properties and from the structural properties and purity of homoepitaxial films grown on them by various techniques such as plasma-assisted molecular beam epitaxy, pulsed laser deposition, magnetron sputtering, chemical vapor deposition, metalorganic chemical vapor epitaxy, liquid phase epitaxy.     

Does the entropy and volume dependence of the structural α-relaxation originate from the Johari–Goldstein β-relaxation?

Conventional theories of glass transition are focussed on reproducing the thermodynamic and dynamic properties of the structural α-process. However, in the last decade a class of secondary relaxations, called the Johari–Goldstein (JG) β-relaxations, has attracted attention in view of the existence of various correlations and similarities of its properties with the structural α-process. These experimental evidences suggest that the secondary process may play a fundamental role in glass transition, and any theory of glass transition would be incomplete until the inter-relations between the JG β-relaxation and the structural relaxation have been considered. In this paper, some significant experimental results showing several general and nontrivial connections between structural relaxation and JG β-relaxation are reported. In particular, these connections indicate that, like the structural relaxation, the JG β-relaxation is entropy and volume dependent. The experimental facts are consistent with the results of the coupling model.     

价态和结构对VO2薄膜热致相变光电性能的影响

本文通过合理控制真空还原时间和真空还原温度,利用真空还原V2O5的方法制备出具有优良热致相变性能的VO2薄膜;通过研究不同真空还原时间及真空退火温度对VO2薄膜结构和热致相变过程中光电性能的影响,得到最佳真空还原参数;制备的薄膜高／低温电阻变化最大达3个数量级;900nm波长光透过率在相变前后改变了40％左右,光学特性相变响应参数较大,热致相变性能优良,利用XPS,XRD对不同条件制备薄膜的化学状态和结晶状态进行了研究,结果表明较低温度退火有利于V^5 离子的还原,而升高退火温度可改善结晶状态,退火时间对VO2中结晶状况和V离子价态有显著影响,讨论了离子价态和样品结晶状态对VO2薄膜热相变过程中热滞回线的宽度,相变温度点的影响。     

Relationship between the imperfection of Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> garnet samples of different crystallographic orientations and their physical properties

The kinetic, optical, and dielectric properties of Y₃Fe₅O₁₂ garnet single crystals of different structural quality have been investigated. It is established that the ratio of the intensities of coherent and incoherent scattering characterizes the conduction electron concentration in inhomogeneous magnetic samples. A correlation between the physical properties of the samples and the character of their structural inhomogeneity is revealed.     

X-ray diffraction studies of sprayed SnO2: Sb films

Antimony-doped tin oxide films were deposited by spray pyrolysis on Corning 7059 substrates. The structural and electrical properties of the films deposited with different doping levels were studied. Relative variations in the structural properties were explained on the basis of structure factor calculations. The results show that the incorporation of antimony atoms takes place only at substitutional sites. As expected, the substitutional replacement of tin by antimony atoms increased appreciably the free carrier density of the film.     

Vacancy-induced densification of silica glass

We investigate vacancy-induced densification of silica glass using molecular dynamics simulations. Equilibration of defective glasses initially with various concentrations of vacancies yields glasses denser than the intact glass. The structural and vibrational properties of the densified glasses are characterized. Densification is related to structural changes induced by atomic rearrangement near vacancies, and increases with the concentration of vacancies. Vacancies may cluster and form voids, and the maximum densification for void-structured glasses occurs at a critical radius of about 0.44 nm. The glasses densified by vacancies and by simulated UV-laser irradiation display nearly identical structural and vibrational properties. These results appear to support the Douillard–Duraud point defect model as a common mechanism for radiation densification of silica glass.     

Interdiffusion phenomena in InGaAs/GaAs superlattice structures

We have studied structural properties of InGaAs/GaAs superlattice sample prepared by Molecular Beam Epitaxy (MBE) using high resolution X‐ray diffractometer (HRXRD). Increasing strain relaxation and defect generations are observed with the increasing Rapid Thermal Annealing (RTA) temperature up to 775 °C. The higher temperatures bring out relaxation mechanisms; interdiffusion and favored migration. The defect structure and the defects which are observed with the increasing annealing temperature were analyzed. Firstly, the in‐plane and out‐of‐plane strains after the annealing of sample were found. Secondly, the structural defect properties such as the parallel X‐ray strain, perpendicular X‐ray strain, misfit, degree of relaxation, x composition, tilt angles and dislocation that are obtained from X‐ray diffraction (XRD) analysis were carried out at every temperature. As a result, we observed that the asymmetric peaks especially in asymmetric (224) plane was affected more than symmetric and asymmetric planes with lower polar or inclination angles due to c‐direction at low temperature. These structural properties exhibit different unfavorable behaviors for every reflection direction at the increasing temperatures. The reason is the relaxation which is caused by spatially inhomogeneous strain distribution with the increasing annealing temperature. In the InGaAs superlattice samples, this process enhances preferential migration of In atoms along the growth direction. Further increase in the annealing temperature leads to the deterioration of the abrupt interfaces in the superlattice and degradation in its structural properties. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Properties of non‐stoichiometric nitrogen doped LPCVD silicon thin films

The influence of nitrogen on the internal structure and so on the electrical properties of silicon thin films obtained by low‐pressure chemical vapor deposition (LPCVD) was studied using several investigation methods. We found by using Raman spectroscopy and SEM observations that a strong relationship exists between the structural order of the silicon matrix and the nitrogen ratio in film before and after thermal treatment. As a result of the high disorder caused by nitrogen on silicon network during the deposit phase of films, the crystallization phenomena in term of nucleation and crystalline growth were found to depend upon the nitrogen content. Resistivity measurements results show that electrical properties of NIDOS films depend significantly on structural properties. It was appeared that for high nitrogen content, the films tend to acquire an insulator behavior. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of initial growth parameters on the structural and optical properties of GaAs on (001) Si

The structural and optical properties of GaAs on (001) Si substrates were investigated by transmission electron microscopy (TEM) and low-temperature photoluminescence (PL). It was found that the success of the two-step growth technique is controlled by the quality (morphology and defect density) of the low-temperature grown AlGaAs nucleation layer. GaAs epilayers grown on low V/III ratio AlGaAs nucleation layers exhibit improved surface morphologies and structural properties. These results were confirmed by optical measurements where it was shown that the best PL response was obtained from GaAs epilayers in which the initial AlGaAs nucleation layers were deposited at a low V/III ratio.     

Structural model of gelation processes of a sodium silicate sol destabilized by calcium ions: combination of SAXS and rheological measurements

This study deals with the physico-chemical processes involved in the formation of basic fractal silica gels derived from a sodium silicate sol destabilized by calcium ions. Using small-angle X-ray scattering and dynamic rheological measurements, structural and viscoelastic properties have been investigated in situ during aggregation and gelation processes. The experimental results lead to a consistent model that describes the structural features and aggregation mechanisms involved in the formation of these gels.     

γ-Fe2O3/SiO2 nanocomposites for magneto-optical applications: Nanostructural and magnetic properties

Monolithic nanocomposites consisting in γ-Fe₂O₃ (maghemite) nanoparticles embedded in a silica gel have been prepared as potential magneto-optic materials, suitable for magnetic field sensing. The effects of several processing parameters on the structural and magnetic properties of the samples were evaluated to optimize their performance. Their structural properties have been studied by means of X-ray diffraction, thermogravimetric analysis and transmission electron microscopy, while the magnetic behavior has been characterized by Mössbauer spectroscopy and Faraday magnetometry. Our results indicate that maghemite crystallization conditions must be carefully controlled to obtain nanoparticles of an adequate size and to avoid subsequent evolution to other undesired ferric oxide phases.     

Influence of Dye Molecules on the Polarization of Ferroelectric Vinylidene Fluoride Copolymer

Crystallography Reports - Electrical, electromechanical, and structural–optical properties of films of vinylidene fluoride copolymer with tetrafluoroethylene TFE, doped with Rhodamine 6G dye,...     

Study of batch maltitol (4-O-α-d-glucopyranosyl-d-glucitol) crystallization by cooling and water evaporation

It is obvious that maltitol, like other disaccharides, owes some of its functional properties to structural features such as the flexibility of the glycosidic bond and hydrogen bonding and to its aqueous solution physicochemical properties, especially solubility and metastable zone width. This is particularly the case for molecular arrangements, which take place before and during crystallization process. We have previously used FTIR spectra to study structural properties of the maltitol molecule in concentrated solution like molecular associations or changes in conformation [1]. To complement these molecular properties, the different maltitol solution physicochemical properties having a relationship with maltitol–water or maltitol–maltitol interactions like solubility, metastable zone width, viscosity, and density were determined [2]. In this work we used these physicochemical results to optimize maltitol crystallization both by reducing the process duration and by improving the obtained crystal quality. Two strategies have been tested: the optimization of the time/temperature profile during the classical cooling crystallization and the application to maltitol of evaporative crystallization, a process usually used for sucrose preparation. The obtained results mainly showed remarkable difference in crystal mean size and crystal size distribution when the cooling profile was modified. On the other hand, evaporative crystallization was shown to make it possible to lower considerably the crystallization time compared to the cooling process but crystal morphological properties seem to be considerably modified by evaporation.     

Behavior Study of ZnO Thin Films Grown by PLD for Several Applications

Crystallography Reports - In this work, the effects of glass and Si polycrystalline substrates on structural, morphological, optical and electrical properties of zinc oxide thin films (ZnO)...     

Theoretical Study of Structural,Electronic, Optical,and Elastic Properties of KLiX (X: S,Se, and Te) under Hydrostatic Pressure: A Pseudo Potential Plane Wave (PP-PW) Contribution

Crystallography Reports - We have studied structural, electronic, optical, and elastic properties of KLiX under pressure using the Density Functional Theory (DFT) within the Generalized Gradient...     

Halide glasses

The reasons for the formation of vitreous materials in halide systems are discussed in relation to the nature of the chemical bond. A review of fluoride, chloride, bromide and iodide glasses is presented and discussed in terms of stability and technical interest. The most interesting physical properties, especially optical, include the potential of ultra-low loss fiber for power and telecommunications applications. Recent structural investigations by X-ray, computer simulation, etc, allow the presentation of structural models explaining the glass formation by references to the corresponding crystalline halide materials. A structural systematic is described and compared with the traditional oxide glasses.     

VHF-PECVD制备不同氢稀释条件下硅薄膜特性分析

本文集中报导了不同硅烷浓度条件下,制备的系列硅薄膜电学特性和结构特性的分析研究。结果表明：随着硅烷浓度的逐渐减小,材料逐渐地由非晶向微晶转变。傅立叶变换红外吸收(FFIR)的测试结果表明：微晶硅材料存在着自然的不稳定性,表现为氧含量随着时间的推移而增多。而且,微结构因子(IR)的结果给出：对于适用于电池有源层的微晶硅材料来说,其IR不能太大,也不能太小,本实验中相对好的微晶硅材料其IR为31％。