New composite materials based on fullerenes

New composite materials based on fullerenes are presented. To synthesize these materials, mixtures of polycrystalline C₆₀ powders with various hydrocarbon binding agents and dopants were exposed to high pressures and temperatures. As a result, strong insoluble samples were obtained. Halogens and sodium were used as acceptor and donor admixtures, respectively. In the latter case, a superconductor was prepared, which retained its properties in the course of long storage in air.     

具有各向异性的梯度颗粒复合材料的有效介电响应

本文研究了具有梯度壳层椭球颗粒复合体系的有效介电响应，在稀释条件下用准静态近似方法, 推导了颗粒壳层具有任意介电梯度形式的椭球颗粒复合体系的有效介电常数和部分共振条件的一般表达式。并以壳层的介电常数为主轴的幂函数形式为例，得出了通过调节壳层的介电梯度形式、颗粒的结构和形状,可以提高该体系的有效介电常数和实现部分共振的结论。     

基于空耦超声的复合材料黏弹性评价方法*

复合材料的黏弹性是表征其内在阻尼机制的重要力学特性,而内在阻尼机制是材料安全性能的一个重要评价指标。该文提出了空气耦合超声波的材料黏弹性评价方法。首先讨论了黏弹性进行评价的相关理论,利用接触式超声波底面回波法与空气耦合超声波透射法对比验证,其结果基本一致,证明了空气耦合超声对材料黏弹性检测的有效性。并且对一批不同铺层方向的碳纤维复合材料进行了评价,其结果与期望值完全相符,验证了该方法的可行性和准确性,为复合材料的动态力学特性评价和安全评价提供了新的思路。     

Effective dynamic properties of 3D composite materials containing rigid penny-shaped inclusions

The propagation of time-harmonic plane elastic waves in infinite elastic composite materials consisting of linear elastic matrix and rigid penny-shaped inclusions is investigated in this paper. The inclusions are allowed to translate and rotate in the matrix. First, the three-dimensional (3D) wave scattering problem by a single inclusion is reduced to a system of boundary integral equations for the stress jumps across the inclusion surfaces. A boundary element method (BEM) is developed for solving the boundary integral equations numerically. Far-field scattering amplitudes and complex wavenumbers are computed by using the stress jumps. Then the solution of the single scattering problem is applied to estimate the effective dynamic parameters of the composite materials containing randomly distributed inclusions of dilute concentration. Numerical results for the attenuation coefficient and the effective velocity of longitudinal and transverse waves in infinite elastic composites containing parallel and randomly oriented rigid penny-shaped inclusions of equal size and equal mass are presented and discussed. The effects of the wave frequency, the inclusion mass, the inclusion density, and the inclusion orientation or the direction of the wave incidence on the attenuation coefficient and the effective wave velocities are analysed. The results presented in this paper are compared with the available analytical results in the low-frequency range.     

Independently tunable transmission-type magneto-optical isolators based on multilayers containing magnetic materials

We investigate the magneto-optical (MO) properties of multilayers containing several magnetic defects. Our numerical simulations show that each MO defect mode can be tuned independently by adjusting the structural parameters of magnetic materials. In addition, giant Faraday rotation can be obtained. Our results indicate that the structure may have potential applications for independently tunable multichannel MO isolators.     

Thermoelectric composite materials based on intermediate-valence cerium and ytterbium intermetallic compounds

An important thermoelectric characteristic-the power factor of composite thermoelectric materials—is calculated on the basis of performed measurements of the thermopower, electric conductivity, thermal conductivity, and reference data. The investigated composites consist of intermediate-valence CeNi and YbAl₃ intermetallic systems and elementary metals, nickel and chromium. On account of the specific transport properties of a heterogeneous medium, it becomes possible to increase the value of the power factor in composites at a sufficiently low concentrations of rare-earth-element-based intermetallic compounds. The dependences of the composite-thermoelectric-material power factor on the temperature and the mass fraction of valence-instable components are obtained.     

Spectroscopic and photoluminescence characteristics of Dy ions in lead containing sodium fluoroborate glasses for laser materials

Lead containing calcium zinc sodium fluoroborate (LCZSFB) glasses doped with different concentrations of trivalent dysprosium ions were prepared and investigated by the XRD, FTIR, optical absorption, photoluminescence and decay curve analysis. The experimentally determined oscillator strengths have been determined by measuring the areas under the absorption peaks and the Judd–Ofelt (J–O) intensity parameters were calculated using the least squares fit method. From the evaluated J–O parameters the radiative transition probability rates, radiative lifetimes and branching ratios were calculated for ⁴F_9/2 excited level. Room temperature photoluminescence spectra for different concentrations of Dy³⁺-doped LCZSFB glasses were obtained by exciting the glass samples at 386 nm. The intensity of Dy³⁺ emission spectra increases with increasing concentration of 0.1, 0.25, 0.5 and 1.0 mol% and beyond 1.0 mol% the concentration quenching is observed. The measuring branching ratios are reasonably high for transitions ⁴F_9/2→⁶H_15/2 and ⁶H_13/2, suggesting that the emission at 484 and 576 nm, respectively, can give rise to lasing action in the visible region. From the visible emission spectra, yellow–blue (Y/B) intensity ratios and chromaticity color coordinates were also estimated. The lifetimes of ⁴F_9/2 metastable state for the samples with different concentrations were also measured and discussed.     

Application of Bruggeman and Maxwell Garnett homogenization formalisms to random composite materials containing dimers

The homogenization of a composite material comprising three isotropic dielectric materials was investigated. The component materials were randomly distributed as spherical particles, with the particles of two of the component materials being coupled to form dimers. The Bruggeman and Maxwell Garnett formalisms were developed to estimate the permittivity dyadic of the homogenized composite material (HCM), under the quasi-electrostatic approximation. Both randomly oriented and identically oriented dimers were accommodated; in the former case the HCM is isotropic, whereas in the latter case the HCM is uniaxial. Representative numerical results for composite materials containing dielectric–dielectric dimers demonstrate close agreement between the estimates delivered by the Bruggeman and Maxwell Garnett formalisms. For composite materials containing metal–dielectric dimers and metal–metal dimers with moderate degrees of dissipation, the estimates of the two formalisms are in broad agreement, provided that the dimer volume fractions are relatively low. In general, the effects of intradimer coupling on the estimates of the HCM’s permittivity are relatively modest but not insignificant, these effects being pronounced by anisotropy when all dimers are identically oriented.     

The properties of a metal-semiconductor-metal system based on oxide glasses

This paper reports the results of a study of the volt-amp characteristics over a broad temperature range (+200 to –100) ° C of metal-semiconductor-metal structures based on glasses in the V₂O₅-TeO₂ system and on a V₂O₅ polycrystalline aggregate. The electrically formed specimens have symmetrical volt-amp characteristics with an S-type negative resistance region. The temperature dependence of the volt-amp characteristics for these specimens is different from that observed in unformed structures. It is suggested that during forming there is the precipitation of crystalline grains of VO₂ in the interelectrode region and these undergo a phase change which results in the behavioral differences between the formed and unformed specimens.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 57–63, February, 1972.The authors would like to thank E. A. Zamotrinskaya and T. K. Terenik for the supply of glass and V₂O₅.     

Independently tunable omnidirectional multichannel filters based on the fractal multilayers containing negative-index materials

We propose and demonstrate an independently tunable omnidirectional multichannel filter by combining the advantages of the independently tunable filtering properties of fractal structures and the omnidirectional resonant modes of one-dimensional photonic crystals containing negative-index materials. Compared to the conventional multichannel filters, each channel of the proposed filter can be tuned separately, and the frequency position of the filter is insensitive to the incident angle of light. It thus provides a simple way for designing omnidirectional multichannel filters with specific channels.     

Formation and crystallization of ZrCuTi metallic glasses

We report the suction casting of Zr₆₅Cu₂₇Ti₈ bulk metallic glasses with diameters up to 1?mm. While the substitution of Ti for Cu increases the glass forming ability significantly, the onset crystallization temperature and the width of the supercooled liquid region decrease. This decrease is due to the appearance of an icosahedral quasicrystal phase, which crystallises from the glass at a lower temperature than the Zr₂Cu devitrification product in the Zr₆₅Cu₃₅ glasses. Based on the results of recent structural studies of undercooled Ti/Zr-based alloys, this likely reflects the formation of icosahedral order in the undercooled liquid, which increases the nucleation barrier for the Zr₂Cu phase during the quench, making glass formation easier.     

Correlations among micro- and macromechanical properties of composite materials based on the interphase concept

In this paper an attempt was made to define microstructural properties of carbon fiber/PP composites, with respect to fiber surface chemistry and morphology. In order to define the effects of the fiber surface sizings and morphology on the polymer microstructure, the interphase and mechanical properties of the composites, carbon fibers with similar, but not identical surface chemistry (CH and CT) were used. Characterization was performed by several techniques: SEM, POM, reflection microscopy, DSC, FTIR, XPS, contact angle measurements. For microstructural analysis, the geometrical method, method of intercept and DIF method were used. It was found that both carbon fibers have a strong influence on the nucleation mechanism and crystallization as well as on the microstructural parameters in the model and macro composites. Nucleation efficiency of the fibers has been confirmed by the nucleation parameter Q, measured by Muchova–Lednicky method and by the interfacial energy parameters. Microstructural analysis based on the photographs obtained by POM, SEM and reflection microscopy has shown that in the CH/PP model and macrocomposites the sieve-grain network was formed, which indicates better mechanical properties. The results obtained for the macromechanical properties of PP composites reinforced with CH and CT have confirmed the prediction based on micostructural analysis.     

Formation of spin light-emitting diodes based on InGaAs/GaAs heterostructures containing ferromagnetic inclusions

The electroluminescence of light-emitting diodes based on heterostructures with InGaAs quantum wells and a delta 〈Mn〉 doped layer in the GaAs barrier is studied. It is shown that the diodes emit circularly polarized light with the degree of polarization depending on the applied magnetic field and on temperature. We assume that the temperature dependences of the degree of polarization are determined by a change in the mutual position of energy levels of Mn ions in the delta layer and of holes in a quantum well.     

Structural investigations of semiconducting barium-vanadate glasses containing iron

Mössbauer and EPR spectroscopic studies are performed on (0.9-z)V₂O₅.ZBaO. 0.1Fe₂O₃ amorphous semiconductors. It is observed that the addition of BaO results in the formation of non-bridging oxygens. For low Z-values the formed non-bridging oxygens are attached to vanadium ions whereas for higher Z-values some of the oxygens attached to Fe³⁺ ions are also converted into non-bridging ones.     

基于高吸水/保水材料的红外隐身复合材料的可行性研究及效能评价

根据战场条件及红外材料的性能要求,在研究高吸水/保水材料特性的基础上对开发基于高吸水/保水材料的红外隐身复合材料的可行性进行研究分析,提出以高吸水/保水材料为基底的红外隐身复合材料的两种设计方案并制备出该红外隐身复合材料样板.通过对其进行红外效果评价,结果表明,该材料若作为军事目标的表面材料能有效改变目标的红外辐射特性...     

Studies on some alkali-phosphate glasses containing antimony and iron oxides

The effect of heat treatment on the Fe²⁺/Fe³⁺ ratio in some alkali phosphate glasses containing antimony and iron oxides has been investigated. Differential thermal analysis, Mossbauer spectroscopy, magnetic susceptibility and density measurements as well as the molar volume calculations were used in this study. The obtained data indicate that all glasses show approximately unchangeable stability. It is found, from the area under the Mossbauer absorption spectra that ferrous transformed gradually to ferric ions and the transformation rate constant was found to be 48 min⁻¹. The elapsed time was found to be 160 min. This transformation represents a first-order solid state reaction. The molar magnetic susceptibility measurements confirm the above results.     

Transmission electron microscopy of composite materials based on hypercrosslinked polystyrenes with nanodispersed inorganic compounds

Nanocomposite materials with magnetic and catalytic properties based on hypercrosslinked polystyrenes (HLP) and inorganic compounds introduced into a polymer by means of chemical precipitation were investigated. Transmission electron microscopy (TEM) revealed that when ferric oxides are precipitated in hypercrosslinked gel-type polystyrene, nanodispersed particles 8 ± 2 nm in size are formed, and when the ferric oxides are precipitated in hypercrosslinked biporous polystyrene, larger nanoparticles (∼16 nm in size) are formed.