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341.
342.
Mn2+doping-induced-effects on commensuration and incommensuration of potassium zinc chloride crystal
Undoped and Mn2+-doped with different concentrations of potassium zinc chloride (KZC) crystals were grown from aqueous solutions by slow evaporation. The dielectric constant (ε), dielectric losses (tan?δ) and ac conductivity (σac) of the crystals in the ferroelectric-commensurate, incommensurate and normal phases have been measured as a function of frequency, in the range 1–100?kHz, and temperature, in the range 300–580?K. Virgin samples were subjected to measurements of the frequency dependence at selected temperatures and measurements of the temperature dependence was then followed using the same samples. The increase of ε with T could be due to a combination of conductivity, structural variations and discommensuration (DC) formation and pinning as well. The increase of tan?δ with temperature was attributed to relaxation loss in addition to conduction loss, which increases more rapidly with temperature. The ac conductivity (σac) and tan?δ along the polar axis of KZC increased significantly with increasing Mn2+ content while ε decreased. σac changed with frequency according to a power law of the form σac?=?f? s where 0.15<s<1.27. A linear decrease of ε and tan?δ with increasing the frequency was also found. The obtained results were treated by considering the effect of Mn2+-doping on stripples nucleation, DC evolution/annihilation, DC-lattice formation and DCs pinning by the crystal lattice and/or structural defects for virgin and thermally treated samples. 相似文献
343.
ABSTRACT Rb+-doped TiO2 nanoparticles with higher photocatalytic activity were prepared by sol–gel method. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive analysis of X-rays (EDAX), and surface area (BET) measurements. The photocatalytic activity for the degradation of rhodamine B (RhB) was evaluated. The effects of calcination temperature, Rb+-doping amount, and the dosage of catalyst in the reaction liquid were investigated. The results showed that Rb+ doping can inhibit phase transformation from anatase to rutile, increase surface area of TiO2 crystals, and reduce crystallite size. TiO2 doped with 1% Rb+ and calcined at 650°C shows much higher photoactivity than the others when the doping level of Rb+ and calcination temperature are 0–5% and 350–850°C, respectively. The kinetics of the degradation of RhB was also analyzed. The kinetics of this reaction fits the pseudo first-order kinetics model well, and the reaction rate constants for pure TiO2 and Rb1-650 are 0.086 min?1 and 0.226 min?1 respectively. Doping with Rb+ improves the photocatalytic activity of TiO2 significantly. 相似文献
344.
345.
通过对La2-xNdxCuO4+δ(0.1≤x≤1.2)体系中滞弹性弛豫与相变内耗性能的研究发现,当0.1≤x≤1.0时,在250K左右存在一个与间隙氧有关的弛豫内耗峰,并且当0.1≤x≤0.4时,弛豫内耗峰峰高随着x值的增大而升高,此时体系为正交结构;当0.5≤x≤1.0时,体系在宏观上呈现四方结构,此时内耗峰峰高随着x<
关键词:
2-xNd<i>xCuO4+δ')" href="#">La2-xNd<i>xCuO4+δ
间隙氧
弛豫内耗峰
相变内耗峰 相似文献
346.
PeiJun Shen WeiZhong Ding YuDing Zhou ShaoQing Huang 《Applied Surface Science》2010,256(16):5094-22345
The reaction mechanism on surface of BaCo0.7Fe0.2Nb0.1O3−δ membrane for reforming coal-gas was studied. The effects of metal particle on membrane surface were concluded. ‘Activation mechanism’ was proposed to be the key for enhancing oxygen permeation of membrane; while the catalyst-bed only takes charge of the reforming reaction. Though not as important as ‘activation mechanism’, the ‘space charge mechanism’ still affects the oxygen permeation of membrane. According to these mechanisms, the new design and surface-modifying strategy of membrane reactor were proposed. 相似文献
347.
《Analytical letters》2012,45(8):1363-1373
Abstract An amperometric enzyme sensor for the determination of gluconolactone in glucose-containing samples has been developed. The interfering glucose is eliminated by an outer anti-interference layer containing hexokinase, whilst the gluconolactone reaches a glucose de-hydrogenase-glucose oxidase layer, where it is converted into glucose (by glucose dehydrogenase) and then transformed by glucose oxidase, the associated oxygen consumption can be measured at the electrode. Gluconolactone is determined over the concentration range, 0.02–1 mmo1/1, with a toleration of glucose concentration up to 2 mmo1/1. 相似文献
348.
《Analytical letters》2012,45(18):2856-2864
This paper highlights the results of a study regarding the impact of geo-climatic conditions, the influence of grape varieties, and harvest year on the isotopic characterization of a wine from a specific vineyard area, using stable isotope ratio analysis by continuous flow mass spectrometry CF-IRMS. This analytical technique has made a significant contribution on wine characterization, by proving the botanical and geographical origin of the wine raw material. A great variability was observed to sap 18O and 2H isotopic ratios for different types of vine (Vitis vinifera plant) from the studied area, Dealu Mare-Valea Calugareasca, reflecting the significant influence of variety on isotopic features. On the other hand, the comparison of stable isotopic fingerprints for rainfall water and sap revealed a close approximation value for 18O isotopic ratio, and an insignificant variation coefficient of 13C isotopic ratio in wine varieties (about 2.85%). The results of isotopic characterization for grape vine sap and original wines for different varieties existing in Dealu Mare-Valea Calugareasca vineyard indicates the relevance of meteorological and viticulture parameters like precipitation, date of vintage, and grape cultivar for wine authentication process. 相似文献
349.
350.
A submodule N of a module M is δ-small in M if N+X≠M for any proper submodule X of M with M∕X singular. A projective δ-cover of a module M is a projective module P with an epimorphism to M whose kernel is δ-small in P. A module M is called δ-semiperfect if every factor module of M has a projective δ-cover. In this paper, we prove various properties, including a structure theorem and several characterizations, for δ-semiperfect modules. Our proofs can be adapted to generalize several results of Mares [8] and Nicholson [11] from projective semiperfect modules to arbitrary semiperfect modules. 相似文献