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再求一段英译中，在线等，急，50金币
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As mentioned in the above section, LiCoO2 can contain a certain amount of cation mixing in a stoichiometry of [Li1−xCoy]Li-site[LixCo1−y]Co-siteO2. With increasing amount of cation mixing, a spinel character becomes dominant in LiCoO2 and the Raman spectrum shows four Raman bands since the spinel phase belongs to the space group [10]. In our samples, while the weak (0 0 3) peak in the XRD patterns indicated a possibility of cation mixing, the Raman spectra indicated the layered structure without cation mixing. Presumably, the amount of cation mixing is not large and the layered character is dominant rather than the spinel character. The weak (0 0 3) peak in the XRD patterns may be ascribed mainly to the reduction of the number of CoO2 layers. Generally speaking, the Raman peak position and linewidth are affected by phonon confinement [11]. In the case of nanocrystalline materials, q vectors in the range of Δq=1/L (L: crystallite size) become Raman active due to the uncertainty principle, which results in frequency shifts and broadenings. The phonon confinement model generates the first-order Raman spectrum from where the integration is carried out over the Brillouin zone, ω(q) is the phonon dispersion, β is a confinement parameter, and Γ0 is the natural linewidth [12]. Comparing the peak positions of the Raman spectrum for each compound, the Raman peak positions shift from 590 to 575 cm−1 (A1g mode), and from 480 to 465 cm−1 (Eg mode). Fig. 4(a) shows the correlation between the inverse of the crystallite size and the peak positions. For comparison, the peak positions for layered nanocrystalline LiCoO2 synthesized through a hydrothermal reaction are also depicted [13] M. Okubo, E. Hosono, J.-D. Kim, M. Enomoto, N. Kojima, T. Kudo, H.S. Zhou and I. Honma, J. Am. Chem. Soc. 129 (2007), p. 7444. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (41)[13]. As shown in Fig. 4(a), both the A1g and Eg peaks monotonically redshift as the crystallite size decreases. However, it should be pointed out that the frequency shift (Δω) seemed too large (20 cm−1 during the decrease in the crystallite size from 50 to 20 nm) because Δω for nanocrystalline LiCoO2 synthesized through a hydrothermal reaction in the context of the lattice expansion model and the phonon confinement model were in the range of 5 cm−1. Therefore, another explanation for the large Δω is needed. Most likely, structural strain at the surface could affect the spectra. As reported in Ref. [14], both homogeneous strain and inhomogeneous strain on nanocrystalline CeO2−y from the Ce3+ could largely shift the Raman peak (20 cm−1). In our samples, the ICP and AAS measurements revealed that the Li/Co ratio was eventually 1.0 for both compounds annealed at 500 and 700 °C. However, if the small amount of Co3O4 indicated in the powder XRD pattern is considered, excess Li+ should exist to give the composition of Li1+xCo(II)xCo(III)1−xO2. Since Co2+ elongates the bonding distance of Co–O compared to Co3+, the redshift of the Raman peak could be explained. In fact, as shown in Fig. 2(d), the nanocrystalline LiCoO2 synthesized from rapid thermal annealing method has spherical edge, while the nanocrystalline LiCoO2 synthesized from the hydrothermal reaction has hexagonal nanoplatelet morphology due to the hexagonal crystallographic space group. Therefore, the former sample should have more surface strain than the latter sample. With lowering annealing temperature, the surface strain might become stronger, which shifts the vibration frequencies, i.e., the Raman peak positions. In contrast to the peak position, the linewidth of each mode showed clear phonon confinement effect in nanocrystalline LiCoO2. Fig. 4(b) shows the correlation between the inverse of crystallite size and linewidth. For comparison, the linewidths for layered nanocrystalline LiCoO2 synthesized through a hydrothermal reaction are also depicted [13]. As shown in Fig. 4(b), the line shape for both A1g and Eg modes became broader with decreasing crystallite size. The correlation between the linewidth and L−1 for the compounds from different syntheses exhibits the same linearity, and a broadening of linewidths is present regardless of the synthesis method. Therefore, the broadening of linewidths can be attributed to the phonon confinement effect due to the narrow crystal boundary, where q vectors in the range of Δq=L−1 become Raman active by the uncertainty principle. In the phonon confinement model, it is well known that there is a linear correlation between the Raman linewidth and L−α, where α is a scaling exponent equal to d/2 (d: dimensionality) [15]. The solid lines in Fig. 4(b) represent the least-square fitting results using the equation From Journal of Physics and Chemistry of Solids Volume 69, Issue 11, November 2008, Pages 2911-2915 |
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wypward(金币+1):谢谢参与，欢迎新虫 2010-06-08 12:52:33
wypward(金币+1):谢谢参与，欢迎新虫 2010-06-08 12:52:33
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从后往前翻译哈~ 看最后两段： 与峰位置相反，每个样的谱线宽度都显示出耐米超微晶合金LiCoO2中存在清晰的声子局域效应。图4(b)表明了晶体尺寸与谱线宽度的成反比相关。作为对照，将通过热液反应合成的层状LiCoO2的谱线也在图中绘出。图4(b)中，A1g 和 Eg试样的线型随着晶体尺寸的减小而变宽。不同方法合成出来的化合物都表现出一致的谱线宽和L−1的相关性。因此，谱线变宽可以归因于很窄的晶限导致的声子局域效应。由于测不准原理，晶限中的q矢量在Δq=L−1的范围内表现出拉曼活性。 |
3楼2010-06-08 12:07:04
4楼2010-06-08 12:07:27
guoqiusong(金币+10):go on! 2010-06-09 21:39:59
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往前两段的翻译： 表面的结构应变极可能会影响谱图。如文献14中报道的，由Ce3+形成的纳米晶CeO2−y表面的匀质应变和非均匀应变都会使拉曼峰发生很大的偏移(20 cm−1)。 我们的实验中，ICP 和AAS 测试表明，在500和700度退火的样品其Li/Co比最后都等于1。但是，如果考虑到粉状XRD图反映的样品中存在的少量Co3O4，就需要在Li1+xCo(II)xCo(III)1−xO2中有过量的Li+存在。由于Co2+使Co–O键长相比于Co3+的加长，拉曼峰的红移就可以解释了。事实上，由图2(d)，由快速热退火合成的LiCoO2纳米晶有球状边缘，而热液反应合成的LiCoO2纳米晶由于六边形的结晶体群而形成六边形的纳米片状形态。因此，之前的样品比后来的样品有更大的表面张力。随着退火温度的降低，表面张力会变大，从而使振动频率改变，也即拉曼峰的位置改变。 |
5楼2010-06-08 12:31:00
6楼2010-06-08 13:23:31