Dielectric properties of liquid-crystal azomethine polymer with a side alkyl-substituted chain,doped with fullerene C<Subscript>60</Subscript>

We studied the actual and imaginary components of the dielectric constant of liquid-crystal azomethine polymer with a side chain, doped with 0.5 wt % of fullerene C₆₀, over a wide range of temperatures and frequencies; measurements were made by means of dielectric spectroscopy. By analyzing the frequency dependence of the dielectric constant, we detected the relaxation processes (α, β₁, and β₂) in the nanocomposite, corresponding to certain modes of molecular motion and described them by the Arrhenius equations (β₁- and β₂-processes) and the Vogel–Fulcher–Tamman equation (α-process). An antiplasticization effect is discovered after doping the polymer with fullerene C₆₀, which manifests itself in increasing the glass transition temperature of the nanocomposite compared to this parameter typical of pure polymer.     

Synthesis,characterization, conductivity and sensor application study of polypyrrole/silver doped nickel oxide nanocomposites

Conducting polymer composites of polypyrrole (PPy) and silver doped nickel oxide (Ag-NiO) nanocomposites were synthesised by in situ polymerisation of pyrrole with different contents of Ag-NiO nanoparticles. The formation of nanocomposites were studied by Fourier transform infrared (FTIR) and UV–vis spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and AC and DC conductivity measurements. The sensitivity of ammonia gas through the nanocomposite was analysed with respect to different contents of nanoparticles. Spectroscopic studies showed the shift in the absorption bands of polymer nanocomposite than that of pure PPy indicating the strong interaction between the nanoparticles and polymer chain. FESEM revealed the uniform dispersion of nanoparticles with spherically shaped metal oxide particles in PPy matrix. The XRD pattern indicated a decrease in amorphous domain of PPy with increase in loading of nanoparticles. The higher thermal stability and glass transition temperature of polymer nanocomposites than that of pure PPy were revealed from the TGA and DSC respectively. The dielectric properties, DC and AC conductivity of nanocomposites were much higher than PPy and these electrical properties increases with the loading of nanoparticles. The nanocomposites showed an enhancement in sensitivity towards ammonia gas detection than PPy.     

First-principles study of transport properties of endohedral Li@C20 metallofullerene

The transport properties of the endohedral Li@C₂₀ metallofullerene are studied using density functional non-equilibrium Green’s function method. The equilibrium conductance of Li@C₂₀ metallofullerene becomes larger than that of the empty C₂₀ fullerene molecule. The I–V curve under low-bias voltage shows the characteristic of metallic behavior; another, the novel negative differential resistance behavior is also observed. It is found that the doping effect of Li atom significantly changes the transport properties of C₂₀ fullerene.     

Physical properties,thermal stability,and glass transition temperature of multi-walled carbon nanotube/polypyrrole nanocomposites

Polypyrrole (PPy) was synthesized and doped with 1, 2, 4, and 8?wt.% of functionalized multi-wall carbon nanotubes (MWCNTs) by in situ polymerization. TGA/DTA analysis of nanocomposites revealed an increase in thermal stability by increasing the CNTs wt.%. Measurement of electrical resistivity showed a reduction in the resistivity of the composites at all temperatures. The glass transition temperature (T_g) of the samples was measured using electrical resistivity measurements and showed that by increasing the amount of functionalized MWCNTs in PPy, its T_g was increased. Temperature dependence of resistivity of pressed pure PPy showed that by increasing the pelletization pressure, the T_g increased. Also the hardness of nanocomposites was increased by increasing the MWCNTs wt.%.     

Reverse phenomena of magnetic field effects and time-resolved EPR spectra in the photogenerated biradical from intramolecular electron-transfer in a phenothiazine–C60 linked compound with a semi-rigid spacer

Photoinduced electron-transfer reactions and magnetic field effects (MFEs) on the decay rates of the photogenerated biradical in a phenothiazine (Ph)–C₆₀ linked compound with a biphenyl group (Ph(BP)C₆₀) were examined in benzonitrile and benzene. Fluorescence and transient absorption spectra indicate that the intramolecular electron-transfer for Ph(BP)C₆₀ from the Ph to the singlet or triplet excited state of C₆₀ was suppressed by the biphenyl group. The decay rates of the photogenerated biradical decreased in the 0–0.2 T magnetic field range and increased in the 0.2–1 T magnetic field range. The reverse phenomena of the MFEs in Ph(BP)C₆₀ were strongly enhanced with increasing temperature and similar to those in Ph(n)C₆₀ (n = 6?12). The MFEs in Ph(BP)C₆₀ can be governed by spin-lattice relaxation and/or spin-spin relaxation mechanisms as observed in Ph(n)C₆₀ (n = 6?12). Time-resolved EPR spectra of Ph(BP)C₆₀ showed absorption, emission, absorption and emission patterns, and are quite different from those in Ph(n)C₆₀ (n = 4?12). The result indicates that the magnitude and distribution of the exchange interaction |2J| in Ph(BP)C₆₀ are smaller than those in Ph(n)C₆₀ (n = 4?12) and charge recombination occurs in the inverted region because the sign of the J is positive.     

Electrical conductivity and dielectric properties of SiO<Subscript>2</Subscript> nanoparticles dispersed in conducting polymer matrix

Electrical and dielectric properties of conducting polypyrrole–wide band gap silica (PPY–SiO₂) nanocomposites have been investigated as a function of temperature and frequency for different concentrations of polypyrrole. The average grain size of the nanocomposites is in the range of 40–80 nm. Impedance spectra reveal two distorted semicircles corresponding to grain and grain boundary effects. The magnitude of conductivity and its temperature variation are significantly different from polypyrrole and silica. A very large dielectric constant of about 4800 at 30 kHz and at room temperature has been observed for the highest concentration of silica. Inhomogeneous behavior of nanocomposites gives rise to high dielectric constant.     

The compressive mechanical properties of Cn (n=20, 60, 80, 180) and endohedral M@C60 (M=Na,Al, Fe) fullerene molecules

The compressive mechanical properties of C_n (n = 20, 60, 80, 180) and endohedral M@C₆₀ (M = Na, Al, Fe) fullerene molecules are investigated using a quantum molecular dynamics (QMD) technique. Energy–strain curves, force–strain curves, endurance load, failure strain corresponding to the endurance load, and compressive stiffness of the fullerene molecules are obtained. The compressive mechanical properties of C₂₀, C₆₀, C₈₀, C₁₈₀ and M@C₆₀ (M = Na, Al, Fe) are discussed. The results show that the larger the magic number n of an empty fullerene, the higher its endurance load and compressive stiffness, but the lower its failure strain, and comparing to the empty C₆₀ fullerene, all the M@C60 molecules have greater endurance capability and failure strain.     

On the Supermolecular Structure of Fullerene C60 Solutions

Small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) techniques were used for investigation of fullerene C₆₀ solutions in toluene and p‐xylene. On all SAXS curves, intensity decreases to some constant value of I_C with increase of scattering angle. The value of I_C depends on concentration non‐monotonically: it first slightly increases, then drops sharply to some minimal value, and then increases again. A qualitative explanation of such dependence is offered. It is supposed that the presence of fullerene C₆₀ in solution suppresses thermal fluctuations of density in the solvent. In combination with the X‐ray data the results obtained for solutions of fullerene C₆₀ by various others techniques (calorimetry, densimetry, etc.) are discussed. Possible models of a supermolecular structure of fullerene C₆₀ solutions in good solvents are considered.     

基于富勒烯C60结构体系的金纳米粒子合成物光学非线性研究

使用532nm,8ns激光脉冲研究了两种新型的基于富勒烯C₆₀结构体系的金纳米粒子合成物的光学非线性.Z-scan实验结果和理论分析的比较表明,材料的非线性吸收强烈地依赖于材料中的配合体,而非线性折射主要来自金纳米粒子的贡献.而且与熟知的C₆₀甲苯溶液光限幅特性作了比较,分析了光限幅机理. 关键词： 60结构体系')" href="#">基于富勒烯C₆₀结构体系 金纳米粒子 等离子体 光限幅     

Cycloaddition of 2′-azidoethyl glycosides to fullerene[C60] under ultrasonic irradiation

The reactions of fullerene[C₆₀] with 2′-azidoethyl 2,3,4,6-tetra-O-acetyl-α-d-mannopyranoside (2a) and 2′-azidoethyl 2,3,4,6-tetra-O-acetyl-β-d-galactopyranoside (2b) under ultrasonic irradiation cause the cycloaddition of 2′-azidoethyl glycosides to fullerene[C₆₀] and lead to d-glycosyl fullerene[C₆₀] derivatives 3a and 3b, respectively. The glycosyl fullerene[C₆₀] derivatives were characterized by ¹H and ¹³C NMR, UV–vis, FAB-MS, FT-IR spectra and were a 1:1 glycoside fullerene [C₆₀]-adduct.     

The study of polystyrene-fullerene solid-phase composites

Polystyrene-based films containing from 0 to 45 mol % of C₆₀ fullerene are investigated. It is found that the introduction of fullerene increases the molecular packing density of polystyrene chains, thus affecting the transport of small molecules through the polymer films. Gas diffusion through the composite films is slower than through the polystyrene films, while the gas-distributing properties of the composites are higher. The dielectric relaxation method shows that the solution-grown films retain the cluster state of fullerene. When the films containing more than 0.15 mol % of fullerene are heated above the glass transition temperature of polystyrene away from air, the relaxation time of the α transition in polystyrene is found to increase. This effect is associated with strong chain interaction via fullerene molecules incorporated into polystyrene-C₆₀ complexes. The NMR spectroscopy method allows us to observe the typical changes in the composites.     

内掺过渡金属非典型富勒烯M@C22(M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni) 几何结构、电子结构、稳定性和磁性的密度泛函研究

采用密度泛函理论中广义梯度近似对非典型富勒烯C₂₂和过渡金属内掺衍生物M@C₂₂(M=Sc,Ti,V,Cr,Mn,Fe,Co和Ni)的几何结构和电子结构进行计算研究.发现非典型富勒烯C₂₂的基态结构是含有一个四碳环的单重态笼状结构.过渡金属原子的掺入明显提高了体系的稳定性. C-M键既有一定共价性又有一定离子性.磁性、能级图、轨道分布和态密度图分析表明: M原子的3d轨道和碳笼的C原子的原子轨道之间存在较强的轨道杂化. Ti, Cr, Fe和Ni内掺的结构出现磁性完全猝灭现象. Sc和碳笼间是弱反铁磁作用, V,Mn和Co与碳笼间是弱铁磁作用.     

等静压下0.75Pb（Mg1/3Nb2/3）O3-0.25PbTiO3陶瓷的介电性能研究

研究了等静压对0.75Pb（Mg_1/3Nb_2/3）O₃-0.25PbTiO₃（PMN-25PT）陶瓷介电温谱的影响,PMN-25PT剩余极化随等静压变化和等静压压致相变.结果表明,随着压力增加,PMN-25PT的介电峰值温度T_m降低,/+{dT_m}/-{dP}≈-4℃/kbar,极化弛豫增强;剩余极化随压力增加连续减小;介电常数对压力的依赖关系与对温度场的依赖相似,压力诱导PMN-25PT发生弛豫铁电—顺电相变,相变为宽化的渐变过程,频率色散和极化弛豫更加强烈和普遍. 关键词： 铌镁酸铅-钛酸铅 等静压 介电弛豫 压致相变     

Effects of strontium on the characteristics of Pb(Zr1/2Ti1/2)O3--Pb(Zn1/3Nb2/3)O3 ceramics

The dielectric and piezoelectric properties of pyrochlore-free lead zirconate titanate-lead zinc niobate ceramics were investigated systematically as a function of Sr doping. The powders of Pb_{(1? x )}Sr _x [0.7(Zr_{1 / 2}Ti_{1 / 2})–0.3(Zn_{1 / 3}Nb_{2 / 3})]O₃, where x?=?0–0.06 were prepared using the columbite-(wolframite) precursor method. The ceramic materials were characterized using X-ray diffraction, dielectric spectra, hysteresis and electromechanical measurements. The phase-pure perovskite phase of Sr-doped PZN--PZT ceramics was obtained over a wide compositional range. The results showed that the optimized electrical properties were also achieved at composition x?=?0.0, which were K _P?=?0.69, d ₃₃?=?670?pC?N^?1, P _r?=?31.9?µC?cm^?2 and ε_rmax?=?18600. Maximum dielectric constant values of the systems decreased rapidly with increasing Sr concentration. Moreover, with increasing Sr concentration dielectric constant versus temperature curves become gradually broader. The diffuseness parameter increased significantly with Sr doping. Furthermore, Sr doping has been shown to produce a linear reduction in the transition temperature (T _m)?=?294.1–12.7x°C with concentration (x). Sr shifts the transition temperature of this system at a rate of 12.7°C?mol^?1%.     

Comparative study of optical parameters of fullerene C60 film at different temperatures

Fullerene C₆₀ thin films on glass substrate (around 2000 ? thickness) were prepared by thermal evaporation technique. The structural, surface morphology and optical properties of the films were studied. The optical properties of fullerene C₆₀ were investigated in the spectral range 200 nm to 900 nm using a UV-Vis spectrophotometer at room temperature as well as at liquid nitrogen temperature (77 K). The optical band gap at room temperature is found to be 2.30 eV, which gradually decreases with lowering the temperature and reaches to 2.27 at 77 K. The thickness and refractive index of fullerene C₆₀ film were calculated by ellipsometry. From the X-ray analysis, we have calculated the grain size, dislocation density, number of crystallite per unit area, and strain of the film at room temperature. The surface morphology of film was analyzed by scanning electron microscope (SEM). The present result show that the fullerene C₆₀ film becomes more conducting at low temperature.     

Effect of oxygen on the electrophysical properties of some carbon allotropes (graphite and C60 fullerene)

The electrophysical properties of powder samples of graphite and C₆₀ fullerene have been studied in vacuum, oxygen ambient, and air. Room-temperature conduction of the samples has a percolative character. An increase of temperature brings about an increase of sample conductivity caused by oxygen desorption from the bulk. A peak-shaped feature not observed before has been found in the temperature behavior of the resistance of finely dispersed C₆₀ and graphite powder samples in the T=310–340 K interval. Oxygen atoms were found to be involved in charge transport in powder samples of graphite and C₆₀ fullerene through their electrical activity on the surface of grains differing in size. Fiz. Tverd. Tela (St. Petersburg) 39, 1703–1705 (September 1997)     

Optical limiting action of C60 doped poly(dimethylacetylendicarboxylate)

The optical limiting action of poly(dimethylacetylendicarboxylate) polymer doped with fullerene C₆₀ has been investigated under irradiation with 10 ns laser pulses at 532 nm. The optical limiting measurements were performed at four different dopant concentrations. The threshold limiting fluence at 0.3 J/cm² was observed at high doping concentrations, with transmission of about 55%. An explanation based on the combination of two-photon absorption and reverse saturable absorption was proposed for its nonlinear optical absorption behavior.     

Effects of Fe2+ substitution on magnetic and dielectric properties of CdCr2S4

The magnetic and dielectric properties of polycrystalline Cd_{1 - x}Fe_xCr₂S₄ (0 ≤ x ≤ 0.9) are investigated. Upon substitution of Cd by Fe, the Curie temperature (T_C) is increased while the saturation magnetization is decreased. A low doping level of Fe increases the permittivity, while a high doping level decreases the permittivity, which is explained by the internal barrier layer capacitor model. Kinks are observed in the temperature-dependent permittivity and loss tangent near T_C for the samples with x= 0.5, 0.7, 0.9, implying the existence of the magnetodielectric effect. Furthermore, with the increase of Fe content, a decrease of anomaly deviation rate induced by internal molecular field is revealed in the permittivity, while an increase is observed for the loss tangent.     

Simple one-step ultrasonic synthesis of anatase titania/polypyrrole nanocomposites

In this work, hybrid nanocomposites based on anatase titania:polypyrrole (TiO₂:PPy) were directly obtained from a simple, one-step, ultrasonic (UT)-assisted synthesis. The properties of these crystalline nanocomposites were compared with those of others fabricated using cold (Cold)-assisted synthesis without any UT assistance, which required a hydrothermal treatment (HT) to yield crystalline anatase titania in the nanocomposite (TiO₂:PPy) at low temperature (130 °C) and in a short time (3 h). The SEM results demonstrated that the UT-assisted synthesis is a feasible method to obtain anatase TiO₂:PPy nanocomposites with controlled morphology using low energy. The Fourier transform infrared (FT-IR) bands of the crystalline nanocomposites exhibited a shift with respect to neat components, which was attributed to the strong interaction between the secondary amine groups (N–H) of PPy and the oxygen from TiO₂. The acceptable absorption in the visible region (λ_max = 670 nm) indicates that these nanocomposites are good candidates for harvesting energy in solar cells. Devices based on these nanocomposites were built to evaluate their electrical properties. An increase in the photocurrent was observed for the devices prepared with the nanocomposites from the UT-assisted synthesis.