共查询到20条相似文献,搜索用时 15 毫秒
1.
《Journal of Non》2006,352(32-35):3598-3602
Thermal lens (TL) measurements were performed in tellurite glasses, 70TeO2–19WO3–7Na2O–4Nb2O5 (mol%), undoped, doped with Er3+ (1.19 × 1020 ions/cm3) and co-doped with Er3+ (1.19 × 1020 ions/cm3)/Tm3+ (1.56 × 1020 ions/cm3). The absolute nonradiative quantum efficiency (ϕ) was determined by the TL method. The ϕ values for Er3+/Tm3+-co-doped and Er3+-doped tellurite glasses were 0.98 and 0.74, respectively. Fluorescence spectra were performed at λe = 488 nm and used to estimate the fluorescence quantum efficiency (η) using the TL results. These values were compared with results obtained by Judd–Ofelt calculations. 相似文献
2.
L.A. Valenzuela J.G.S. Duque C.T. Meneses W.C. Nunes M. Knobel 《Journal of Non》2008,354(42-44):4871-4873
We report structural and magnetic properties of fine particles embedded in an amorphous magnetic matrix. As-quenched amorphous Fe73.5Nb3CuSi13.5B9 ribbons (FINEMET) were submitted to the thermal treatments of several times (1 ? t ? 240 min) at 570 °C using a conventional furnace. The analyses of the X-ray diffraction patterns at room temperature reveal that our samples consist of single phase Fe3Si nanocrystals embedded in a residual amorphous phase. Magnetic measurements show that the saturation moment at T = 450 °C increases as a function of annealing time. This behavior is attributed to an increase of the fraction of nanocrystallites in the residual amorphous phase. 相似文献
3.
《Journal of Non》2006,352(26-27):2829-2833
Hollow silica spheres were synthesized by using a chitosan-polyacrylic acid (CS-PAA) template. Polyacrylic acid (PAA) was titrated into the dissolved chitosan solution to form CS-PAA particles. For forming the core-shell particle, colloidal silica which was prepared from homogeneous nucleation was mixed with a solution of CS-PAA particles. Colloidal silica was adsorbed on to the surface of the CS-PAA particles to form a shell structure. CS-PAA could be removed from the core of the core-shell particles by adjusting with HCl to pH < 1 for forming the hollow silica structure. The outside particle size diameter, shell thickness, specific surface, pore diameter and pore volume of the final hollow silica sphere are about 200 nm, 20 nm, 350.95 m2/g, 5.4078 nm and 0.516768 cm3/g, respectively. 相似文献
4.
In-keun Jung Jyoti L. Gurav Uzma K.H. Bangi Seungsu Baek Hyung-Ho Park 《Journal of Non》2012,358(3):550-556
Synthesis of multi-walled carbon nanotubes (MWCNTs) doped silica xerogel films was reported in this work. A crucial step of introducing MWCNTs was achieved by functionalizing them by acid treatment to form stable and homogenous SiO2/MWCNTs sol. Scanning electron microscopy showed spherical particles in honeycomb network structure for undoped xerogel films whereas dispersion and wrapping of MWCNTs in silica matrix was observed for MWCNTs doped films. Various bond formations during the sol–gel process and surface modification were confirmed using Fourier transform infra-red and detailed study on the chemical bonding state of the films was carried out using X-ray photoelectron spectroscopy. Nanoindentation studies showed that the mechanical properties of MWCNTs doped xerogel film increase dramatically: higher modulus (E = 2.127 ± 0.095 GPa) and hardness (H = 0.035 ± 0.017 GPa) values than those of pristine xerogel film (E = 0.234 ± 0.058 GPa, H = 0.01 ± 0.003 GPa). 相似文献
5.
Jean-Fabien Capsal Eric Dantras Jany Dandurand Colette Lacabanne 《Journal of Non》2011,357(19-20):3410-3415
Thermo Stimulated Current and Dynamic Dielectric Spectroscopy studies were carried out on hybrid ferroelectric Polyamide 11/Barium Titanate to investigate dielectric relaxation modes. The correlated results obtained by both methods allow us to describe precisely the molecular mobility of this 0–3 nanocomposite; in this work we will focus on the influence of the 700 nm nanoparticles volume fraction. The dielectric spectroscopy shows that the molecular mobility associated with the liquid dynamic is not influenced by the volume fraction. The evolution of low frequency relaxation, observed by depolarization currents techniques, have been attributed to the decrease of Cooperative Rearranging Region size and the increase of intra/inter macromolecular interactions in the soft amorphous phase. 相似文献
6.
Nickel nanowires with high aspect ratio (250) were elaborated and incorporated into poly(vinylidene difluoride-trifluoroethylene) up to 30 vol% via solvent mixing way. These nanocomposites are characterized by a conductive behavior with a high electrical conductivity value (102 S m?1) above a very low percolation threshold (0.75 vol% of metallic nanowires). The introduction of nanowires strongly depressed the matrix crystallinity. Static and dynamic mechanical analysis have been realized at low nanowire volume fraction (< 10 vol%). Below 5 vol% of nanowires, nanocomposites remain ductile. The dynamic mechanical properties are related to the volume fraction of nanowires. A strong increase of the viscoelastic contribution related to the increase of the percentage of amorphous phase is observed. The major effect is the increase of the rubbery modulus. The highest increase of 300% is obtained for only 5 vol% of nanowires; it represents an original mechanical result for low filled composites. The dependence versus nanowire content has been described by adapting the Halpin–Tsai model to high aspect ratio filler. Metallic nanowires create additional entanglements that are randomly distributed in the rubbery polymeric matrix. With their low percolation threshold, metallic nanowires based nanocomposites constitute a new class of multifunctional materials with a high conductivity associated with a ductile polymer matrix characterized by a high rubbery modulus. 相似文献
7.
Randilynn Christensen Jennifer Byer Garrett Olson Steve W. Martin 《Journal of Non》2012,358(3):583-589
The mixed glass former effect (MGFE) is defined as a non-linear and non-additive change in the ionic conductivity with changing glass former fraction at constant modifier composition between two binary glass forming compositions. In this study, mixed glass former (MGF) sodium borophosphate glasses, 0.35 Na2O + 0.65 [xB2O3 + (1 ? x)P2O5], 0 ≤ x ≤ 1, which have been shown to have a strong positive MGFE, have been prepared and their physical properties, density and molar volume, have been examined as predictors of structural change. The density exhibits a strong positive non-linear and non-additive change in the density with x and a corresponding negative non-linear and non-additive change in the molar volume. In order to understand the structural origins of these changes, a model of the molar volume was created and best-fit to the experimentally determined molar volumes in order to determine the volumes of the short range order (SRO) structural units in these glasses, how these volume change from the molar volumes of the binary glasses, and how these volumes change across the range of x in the ternary glasses. The best-fit model was defined as the model that required the smallest changes in the volumes of the ternary phosphate and borate SRO structural groups from their values determined by the densities of the binary sodium phosphate and sodium borate glasses. In this best-fit molar volume model, it was found that the volumes of the various phosphate and borate SRO structural groups decreased by values ranging from a minimum value of ~ 1% for x = 0.1 and 0.9 to a maximum value of ~ 6% for the phosphate and ~ 9% for the borate SRO groups at the minimum in molar volume at x = 0.4. The free volume was found to have a negative deviation from linear which is unexpected given the positive deviation in ionic conductivity. 相似文献
8.
《Journal of Non》2007,353(44-46):4076-4083
Structural and thermal properties are reported for a range of caesium oxide-containing alkali borosilicate glasses, of the form xCs2O(100 − x)ZMW (0 < x < 10), where ZMW represents a variety of simulated base-glasses. Glass densities increase and glass transition temperatures decrease with increase in caesium oxide concentration. Mass-loss from the melt is found to depend on composition in the same manner as the fraction of silicon Q3 units, resolved from 29Si MAS NMR, and is related to the presence of danburite medium-range order units, resolved from 11B MAS NMR. Volatilization is shown to occur even in the absence of caesium oxide and the mixed alkali borosilicate composition of the volatile species, evolved from the melt at high temperature, is independent of the starting composition of the glass. 相似文献
9.
《Journal of Non》2007,353(8-10):811-813
Barium ferrite nanoparticles were synthesized by hydrothermal method. The grain size of BaFe12O19 produced chemically at temperatures between 150 and 200 °C with a reaction time of 12 h varies from 9 to 15 nm. At 4.2 K a grain size independent coercive field of about 1.2 kOe was found. However, at 300 K, the coercivity changes from 230 Oe up to 590 Oe. The magnetization at 4.2 and 300 K increases linearly with grain size. In TEM images it can be seen, that the materials are composed of plate-like and stick-like particles. The amount of the stick-like particles increases with synthesis temperature. The low values of the coercivity at 300 K are discussed in terms of demagnetising field and the nearness of the blocking temperature. The increase of the magnetization with reaction temperature may be attributed to the increase of grain size. 相似文献
10.
《Journal of Non》2007,353(44-46):4048-4054
The nanostructural, chemical, and optical features of AlxSi0.45−xO0.55 (0 ⩽ x ⩽ 0.05) thin films were investigated in terms of Al concentration and post-deposition annealing conditions; the films were prepared by co-sputtering a Si main target and Al-chips, and the annealing was carried out at temperatures of 400–1100 °C. The a-Si0.45O0.55 films prepared without Al-chips and annealed at 800 °C contain ∼3.5 nm-sized Si nanocrystallites. The photoluminescence (PL) intensity as well as the volume fraction of Si nanocrystallites increased with increasing the concentration of Al to a certain level. In particular, the intensity of the PL spectra of the Al0.025Si0.425O0.550 films which were annealed at 800 °C increased significantly at wavelengths of ∼580 nm. It is highly likely that the observed increase in the PL intensity is caused by the raise in the total volume of the ∼3.5 nm-sized nanocrystallites in the films. The addition of Al as well as the post-deposition annealing allow adjustment and control of the nanostructural and light-emission features of the a-SiOx films. 相似文献
11.
《Journal of Non》2007,353(16-17):1635-1644
The development of the structure of silica/alumina gels was investigated by small angle X-ray scattering (SAXS) through all stages of the preparation process, that is gelation, aging, drying and calcination. Two series of gels were compared; the first was prepared from a single-source precursor, obtained by reaction of 3-oxoethyl-6-trimethoxysilyl-hexan-2-one (OTH-H) with Al(OsBu)3. The gels of the second series were prepared from the same precursors, but under conditions where hydrodeacylation of OTH-H occurs. It turned out that both series showed a similar structural development of the gels. Immediately after the start of the reaction small primary particles are formed, the size of which (r = 0.7 ± 0.1 nm) remains constant through the gelation and aging process. In some samples, Si(OEt)4 was added as an additional source for Si/O which was incorporated between the primary particles. Condensation proceeds by a slower aggregation of the primary particles, which initially form a rather open network. This network densifies during aging and drying. 相似文献
12.
Fumitaka Ohashi Masashi Hattori Takuya Ogura Yuzo Koketsu Roto Himeno Tetsuji Kume Takayuki Ban Tamio Iida Hitoe Habuchi Hironori Natsuhara Shuichi Nonomura 《Journal of Non》2012,358(17):2134-2137
To develop an efficient synthesis of type-II Si clathrates with low Na content (NaxSi136: x = 0–24), various conditions for annealing the Zintl phase NaSi were examined. The addition of a pre-annealing process under vacuum at 250 °C following the preparation of NaSi resulted in a decrease in the Na content of type-II Si clathrates from 4 to 2 when the pre-annealing duration ranged from 0 to 60 h, while the volume fraction of type-II Si clathrate crystals in the synthesized specimens (type-II/(type-I + type-II + d-Si)) deduced by powder X-ray diffraction and Rietveld analysis was maintained at approximately 85%. These preparation techniques that enable the high-yield synthesis of semiconductive type-II Si clathrates open opportunities for the application of these substances to semiconductor devices. 相似文献
13.
Y. Sobajima S. Nakano M. Nishino Y. Tanaka T. Toyama H. Okamoto 《Journal of Non》2008,354(19-25):2407-2410
Microstructures of microcrystalline silicon (μc-Si) deposited at a high-growth-rate have been investigated in order to apply to the photovoltaic i-layer. μc-Si films were prepared by very-high-frequency (100 MHz) plasma-enhanced chemical vapor deposition at 180 °C. High growth rates of 3.3–8.3 nm/s have been achieved utilizing high deposition pressures up to 24 Torr and large input powers. Applying μc-Si to n–i–p junction solar cells, as the optimum result in this experimental series, a conversion efficiency of 6.30% (JSC: 22.1 mA/cm2, VOC: 0.470 V, and FF: 60.7%) has been achieved employing the i-layer deposited at 8.1 nm/s. Raman scattering and X-ray diffraction measurements revealed the crystalline volume fraction of around 50% with the (2 2 0) crystallographic preferential orientation, respectively. The cross-sectional transmission electron microscope image shows densely columnar structure grown directly on the underlying n-layer. These structural features are basically in good agreement those of low-growth-rate μc-Si used for a high efficiency solar cell as previously reported, implying advantages of the use of high pressures with regard to providing the photovoltaic i-layers. Finally, the implication is discussed from the photovoltaic performance as a function of the crystalline volume fraction of i-layer, and current problems in improving the photovoltaic performance are extracted. 相似文献
14.
《Journal of Non》2007,353(22-23):2237-2243
We investigated the kinetics of crystal nucleation, growth, and overall crystallization of a glass with composition close to the stoichiometric 1Na2O · 2CaO · 3SiO2. The nucleation and subsequent growth of sodium-rich crystals in this glass decreases the sodium content in the glassy matrix, drastically hindering further nucleation and growth. Compositional changes of the crystals and glassy matrix at different stages of the crystallization process were determined by EDS. These compositional variations were also monitored by electrical conductivity measurements, carried out by impedance spectroscopy, in glassy, partially, and fully crystallized samples. The electrical conductivity of both crystalline and glassy phases decreases with the increase of the crystallized volume fraction. Starting at a crystallized volume fraction of about 0.5, the crystalline phase dominates the electrical conductivity of the sample. This behavior was corroborated by an analysis of the activation energy for conduction. We show that electrical conductivity is highly sensitive and can indicate compositional shifts, changes in the spatial distribution of mobile ions in the glassy matrix. Conductivity measurements are thus a powerful tool for the investigation of complex heterogeneous systems, such as partially crystallized glasses and glass-ceramics. 相似文献
15.
《Journal of Non》2007,353(8-10):805-807
Co1−xZnxFe2O4 (x = 0, 0.2 and 0.4) fine powders with particles size of 3 nm were prepared by hydrolysis method. The powders were annealed at 500 °C for 3 h. With heat treatment, the average particles size increased to 12 nm with corresponding increase in blocking temperature, saturation magnetization and reduced remanence. A significant increase in coercive field was found only for the pure CoFe2O4. 相似文献
16.
《Journal of Non》2007,353(47-51):4344-4352
We report new results on segmental dynamics and glass transition in a series of poly(dimethylsiloxane) networks filled with silica nanoparticles prepared by sol-gel techniques, obtained by differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC), broadband dielectric relaxation spectroscopy (DRS) and dynamic mechanical analysis (DMA). The nanocomposites are characterized by a fine dispersion of 10 nm silica particles and hydrogen bonding polymer/filler interactions. The first three techniques indicate, in agreement with each other, that a fraction of polymer in an interfacial layer around the silica particles with a thickness of 2–3 nm shows modified dynamics. The DSC data, in particular measurements of heat capacity jump at Tg, are analyzed in terms of immobilized polymer in the interfacial layer. The dielectric TSDC and DRS data are analyzed in terms of slower dynamics in the interfacial layer as compared to bulk dynamics. We employ a special version of TSDC, the so-called thermal sampling (TS) technique, and provide experimental evidence for a continuous distribution of glass transition temperatures (Tg) and molecular mobility of the polymer in the interfacial layer, which is consistent with the DRS data. Finally, DMA results show a moderate slowing down of segmental dynamics of the whole polymer matrix (increase of glass transition temperature by about 10 K as compared to the pure matrix). 相似文献
17.
《Journal of Non》2007,353(30-31):2919-2925
The aim of the present paper is to give structural information in order to set a correlation between the electrical conductivity behavior and structures of lithium and silver vanadium–tellurite based glasses. We report our structural studies and compare the effect of the nature of the metallic cation on glasses of the form XM2O · (1 − X)V2O5 · 2TeO2 (where 0 ⩽ X < 1 and M = Li or Ag). Fourier transform infra-red (FTIR) spectra were recorded for all compositions and complementary differential scanning calorimetry (DSC) measurements and X-ray diffraction (XRD) measurements were also carried out. This paper should be considered as complementary to a previous article reporting the conductive behavior of theses glasses. In the latter we reported the obtained results on electrical conductivity studies. The results confirm the existence of a transition from a typically electronic (polaronic) conductive regimen when the molar fraction (X) of M2O is equal to 0, to an ionic conductive regimen when X tends to 1. The evidence for the independent migration path for both electrons and ions was put into evidence by studying the electrical conductivity behavior in a complementary system of the form X M2O · (1 − X)[0.5V2O5–0.5MoO3] · 2TeO2. In this system vanadium was partially replaced by molybdenum which acts as a ‘diluting’ agent of the active centers involved in the electronic transport. 相似文献
18.
《Journal of Non》2006,352(50-51):5271-5278
Mo tracer diffusion in Fe76Mo8Cu1B15 alloy was studied using serial sectioning method in the temperature range 548–648 K. Sputtering by Ar+ ions was applied as a sectioning technique. The measurement was carried out with the ribbon-like samples in as quenched state (q) and in two states after pre-anneals 683 K/1 h (a1) and 743 K/1 h (a2). The volume fraction of crystalline phase was checked by the Mössbauer spectroscopy. Measured concentration profiles consist of two distinct branches suggesting that two diffusion paths are operating. Diffusion coefficients Dv calculated from the near-surface branch were attributed to Mo volume diffusion in amorphous phase. Their values obtained for (a1) are lower than those obtained for (q) which is due to relaxation of free volume. The higher values, on the other hand, obtained for (a2) are influenced by faster short-circuit diffusion, which was attributed to diffusion in interfacial amorphous phase. Short-circuit diffusivity, P, of Mo was evaluated from concentration tails using both LeClaire’s analysis and Divinski’s theory derived for transition type-A/B regime. 相似文献
19.
Volume and enthalpy relaxation studies of amorphous Se have been performed in the glass transition region by mercury dilatometry and differential scanning calorimetry. For simple temperature jump experiments, as well as for more complex thermal history the volume and enthalpy relaxation data can be described by a single set of kinetic parameters for Tool-Naraynaswamy-Moynihan (TNM) model [Δh1/R = 42.8 kK, ln(ATNM/s) = ?133]. Slightly different non-linearity and non-exponentiality parameter were found for volume [x = 0.42, β = 0.58] and enthalpy [x = 0.52, β = 0.65] relaxation data. Similar results were obtained also for Adam-Gibbs-Scherer (AGS) model. The activation energy of viscous flow in the glass transition range is identical with the effective activation energy for relaxation process. A self-consistent data evaluation shows that at moderate departure from equilibrium, volume and enthalpy in amorphous selenium relax in the same way as expressed by TNM and AGS models. Both volume and enthalpy change can be interpreted within the same fictive temperature concept. 相似文献
20.
The scope of this work is to determine the crystalline phases of devitrified barium magnesium phosphate glasses and the glass composition which presents the best resistance to crystallization. Barium magnesium phosphate glasses with composition xMgO · (1 ? x)(60P2O5 · 40BaO) mol% (x = 0, 0.15, 0.3, 0.4, 0.5, and 0.6) were analyzed by differential thermal analysis (DTA) to evaluate the thermal stability against crystallization, and X-ray diffraction (XRD) to identify the crystalline phases formed after devitrification. The glass transition temperature (Tg) increases as the MgO content increases. The maximum temperature attributed to the crystallization peak in the DTA curve (Tc) increases when x increases in the range 0 ? x ? 0.3, and it decreases for x > 0.3. The most thermally stable glass composition against crystallization is for x = 0.3. After the devitrification, the number of coexisting crystalline phases increases as the MgO content increases. For x = 0.3 there is the coexistence of γBa(PO3)2 and Ba2MgP4O13 phases for devitrified glasses. The trend of the Tc is explained based on the assumptions of changes in the Mg2+ coordination number and the amphoterical features of MgO. 相似文献