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431.
Nanocrystalline Ni(OH)2 powder synthesized by a chemical precipitation method was processed using the planetary ball milling (PBM), and the physical
properties of both the ball-milled and unmilled Ni(OH)2 were characterized by scanning electron microscopy (SEM), specific surface area, particle size distribution, and X-ray diffraction.
It was found that the PBM processing could significantly break up the agglomeration, uniformize the particle size distribution,
increase the surface area, decrease the crystallite size, and reduce the crystallinity of nanocrystalline β-Ni(OH)2, which were advantageous to the improvement of the electrochemical activity of Ni(OH)2. The ball-milled nanocrystalline (BMN) Ni(OH)2 was then used to alter the microstructure of pasted nickel electrodes and improve the distribution of the active material
in the porous electrode substrate. Electrochemical performances of pasted nickel electrodes with a mixture of BMN and spherical
Ni(OH)2 as the active material were investigated, and were compared with those of pure spherical Ni(OH)2 electrodes. Charge/discharge tests showed that BMN Ni(OH)2 addition could enhance the charging efficiency, specific discharge capacity, discharge voltage, and high-rate capability
of pasted nickel electrodes. This performance improvement could be attributed to a more compact electrode microstructure,
better reaction reversibility, and lower electrochemical impedance, as indicated by SEM, cyclic voltammetry, and electrochemical
impedance spectroscopy. Thus, it was an effective method to modify the microstructure and improve the electrochemical properties
of pasted nickel electrodes by adding an appropriate amount of BMN Ni(OH)2 to spherical Ni(OH)2 as the active material. 相似文献
432.
433.
Nanocrystalline CeO2-doped (5, 7.5, 10, and 15 mol%) Gd2O3 powders, with a particle size of about 17 nm, were synthesized through the combustion of glycine/nitrate gels. Dense nanocrystalline
materials were obtained by hot uniaxial sintering. Optical microscopy, scanning electron microscopy and transmission electron
microscopy examinations, as well as X-ray diffraction analyses, have allowed us to characterize these polycrystals. The grain
sizes, included between ∼10 and 80 nm, depend on both the sintering temperature and the amount of dopant. A comparison of
the transport properties of these nanocrystalline samples to the values obtained with coarsened grained materials of same
composition shows that the ionic conductivity passes through a maximum for mean grain sizes included between 300 and 500 nm.
Furthermore, an enhancement of the ionic conductivity is observed when the amount of dopant increases. This was attributed
to a grain-size-dependent gadolinium segregation at the periphery of the grains confirmed by X-ray photoelectron spectroscopy
characterizations.
Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, France, 9–15 Sept. 2007. 相似文献
434.
Ramphal Sharma Anil Ghule R. Joshi J.C. Vyas T. Ganesh Wonjoo Lee 《Applied Surface Science》2009,255(18):8158-8163
Nanocrystalline CuIn3Se5 thin films have been grown on ITO glass substrates using chemical ion exchange reactions with CdS, in alkaline medium at pH 11. The as-deposited films were annealed in air at 200 °C for 30 min and characterized using X-ray diffraction (XRD), transmission electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy to study the structural, compositional and morphological properties. The XRD patterns reveal the nanoparticles size to be of 18-20 nm diameter, while from the SEM images the nanoparticles size is estimated to be 20-30 nm. It is observed that the annealed films contain nanocrystallites connected with each other through grain boundaries, with grain size of about 100-125 nm and have an overall n-type electrical conductivity and higher photoconductivity. The current-voltage (I-V) characteristics (in dark and light) of these films indicated the formation of a Schottky like junction between the n-CuIn3Se5 (OVC) and CdS/ITO layers. 相似文献
435.
We have obtained intense cathodoluminescence (CL) emission from electron beam modified porous silicon films by excitation with electrons with kinetic energies below 2 keV. Two types of CL emissions were observed, a stable one and a non-stable one. The first type is obtained in well-oxidized samples and is characterized by a spectral peak that is red shifted with respect to the photoluminescence (PL) peak. The physically interesting and technologically promising CL is however the CL that correlates closely with the PL. Tuning of this CL emission was achieved by controlling the average size of the nanostructure thus showing that the origin of this CL emission is associated with the quantum confinement and the surface chemistry effects that are known to exist in the porous silicon system. We also found that the electron bombardment causes microscale morphological modifications of the films, but the nanoscale features appear to be unchanged. The structural changes are manifested by the increase in the density of the nanoparticles which explains the significant enhancement of the PL that follows the electron irradiation. 相似文献
436.
The photo-induced change in wettability of hydrophobized TiO2 films has been investigated for steel coated with acidic TiO2 nanosols containing varying concentrations of dispersed nanocrystalline titania, such as Degussa P25. The photo-induced change in wettability was evaluated by measuring the time-dependent drop of water contact angle (WCA) after samples had been soaked in either n-octyltriethoxysilane (OTS) or decanoic acid (DA). TiO2 films treated in this way exhibit superhydrophobic behaviour, with WCA greater than 160°. After radiation with UV (black light), the superhydrophobic properties are transformed into superhydrophilic properties, with WCA of almost 0°. As P25 content and layer thickness increase, high rates of photo-induced change are found, but a moderate calcination regime is required. On the other hand, hardness and E modulus pass through a maximum at 25 wt% P25, so that a P25 content between 25 and 50 wt% is the optimum for practical uses. With such stable coatings, wettability can be controlled over a wide range, and the switch between hydrophobic and hydrophilic states can be carried out repeatedly when DA is used as the hydrophobizing agent. Use of a low calcination temperature (450 °C) for the intermediate annealing of the single layers in multilayer coatings and a short final sintering step at a relatively high temperature (e.g. 630 °C for 10 min) allow the preparation of relatively thin TiO2 films on steel with a high photoactivity. 相似文献
437.
Fe3O4和Zn2+掺杂型Zn1-xFe2+xO4纳米晶的溶剂热合成和电磁性能 总被引:1,自引:0,他引:1
利用溶剂热法, 在醋酸钠静电保护剂的辅助下, 成功制备出Fe3O4和Zn2+掺杂型Zn0.07Fe2.93O4纳米晶. 利用X射线衍射仪和扫描电子显微镜等对样品的晶体结构、粒径、形貌和化学组成进行了分析. 结果表明, 所得纳米晶的粒径均匀, 形貌为球形, 分散度好; Zn0.07Fe2.93O4纳米晶的平均粒径(70 nm)明显小于Fe3O4(170 nm). 磁性能测量结果表明, 室温下Zn0.07Fe2.93O4的饱和磁化强度(54.2 A·m2·kg-1)小于Fe3O4 (81.6 A·m2·kg-1). 利用矢量网络分析仪对样品的电磁性能和吸波性能进行了研究. 结果表明, Zn2+掺杂型Zn0.07Fe2.93O4纳米晶的吸波性能优于Fe3O4, 前者的最大吸收峰(-19.3 dB)大于后者(-9.8 dB), 且吸收峰低于-10 dB的峰宽达2.5 GHz. 相似文献
438.
Ayush Khare 《Journal of luminescence》2010,130(7):1268-1274
Nanocrystalline (Zn-Cd)S films have been co-deposited on glass slide substrates by chemical bath deposition (CBD) technique at 70 °C for 75 min. Electroluminescent (EL), photoluminescent (PL) and structural characteristics of these films doped with Cu have been investigated. Cu doping has significant effects on the growth, structural and optical properties of the deposited (Zn-Cd)S films. EL studies show the essentiality of copper for EL emission. The effect of Cu concentration is examined on XRD, SEM, UV-vis spectroscopy, etc. The morphology of these films investigated with SEM and XRD is used to determine crystalline nature of the films. The optical absorption coefficient of the films has been found to increase with increase in Cu concentration. Voltage and frequency dependence shows the effectiveness of acceleration-collision mechanism. The trap-depth values are calculated from temperature dependence of EL brightness. 相似文献
439.
This paper reports the synthesis of nanocrystalline powders of Co-doped ZnO (i.e. Zn0.9Co0.1O (ZCO)) diluted magnetic semiconductor by a simple method using acetate salts of Zn and Co, and polyvinyl pyrrolidone as precursors. The morphology and crystalline size of the synthesized powders were evaluated by scanning electron microscopy and transmission electron microscopy (TEM). The ZCO powders consist of both nanoparticles with particle sizes of ∼50–100 nm and nanorods with diameters of ∼100–200 and ∼200–500 nm in length. The X-ray diffraction and TEM results indicated that the synthesized ZCO powders had the pure wurtzite structure without any significant change in the structure affected by Co substitution. Optical absorption measurements showed absorption bands indicating the presence of Co ions in substitution of Zn ions. Room-temperature magnetization results revealed a paramagnetic behavior for the ZCO precursor (as grown sample) and a ferromagnetic behavior for the ZCO powders calcined in air at 873 K for 1 h. 相似文献
440.
Optical properties of nanocrystalline silver halides 总被引:4,自引:0,他引:4
Michal Ilana Freedhoff Alfred P. Marchetti George L. McLendon 《Journal of luminescence》1996,70(1-6):400-413
A review of quantum confinement effects in nanocrystals of silver bromide (AgBr) and silver iodide (AgI) is presented. AgBr is an indirect gap semiconductor while AgI has a direct band-to-band lowest energy transition. An examination of the low-temperature optical properties of quantum confined AgBr grown using a variety of synthetic techniques will be made. The dynamics of some of the involved excitonic processes will be measured and discussed in reference to a possible breakdown in the momentum selection rules as the nanocrystals are made smaller. Other explanations for this behavior such as impurity exclusion and surface effects will also be considered, as will the dynamics associated with the trapping of excitons at intrinsic iodide impurities in AgBr. Absorption measurements on AgI nanocrystals will be discussed and compared with the exciton photophysics in AgBr. Both AgBr and AgI display an increasing blue shift of their luminescence, arising from the recombination of excitons, as the crystallite size decreases. The luminescence intensity arising from this process increases with decreasing size in AgBr but it disappears in small crystals of AgI. This leads to the conclusion that in the latter material nonradiative decay channels are opening up as the size decreases. 相似文献