氢在非晶和多晶Ti_2CuH_x中定域振动的研究
NEUTRON SCATTERING STUDY OF HYDROGEN VIBRATIONS IN POLYCRYSTAL AND GLASSY Ti_2CuH_x
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摘要: 利用铍过滤探测器中子谱仪,在50-210 meV的能量范围内,测量了非晶 Ti_2CuH_(1.26)和多晶Ti_2CuH_(1.03)室温下的局域振动谱。从实验曲线可以看出,两者的振动态密度分布虽有某些相似之处,但存在较大的差别:晶态样品的光学支呈现双峰、峰窄,峰位在92和147meV,半宽度为32和54meV;非晶样品却出现一个极宽的氢原子振动能带,峰位与晶态主峰几乎重合,半宽度约为104meV,比相应晶态加宽了近一倍。分析结果表明,在晶态和非晶态Ti_2CuH_?中,氢原子所占据的主要位置虽然都是四面体间隙位置,但由于在非晶材料中,存在着多面体单元结构的畸变和局部化学成分的涨落等现象,氢原子在其中的定域环境的分布更为宽广。Abstract: Neutron vibrational spectra for both amorphous Ti_2CuH_(1.26) and polycrystalline Ti_2CuH_(1.03) are measured in the energy range of 50-210 meV with a beryllium filter detector spectrometer. From the experimental curve it can be seen that although there is somewhat similarity in vibrational density of statesof the hydrogen atoms in these two samples, large differences between them are evident. The optical vi-bration peak of crystalline sample reveals a narrow frequency distribution with a FWHM of 54 meVand apparently consists of two peaks at 92 and 147 meV. In the amorphous sample the optical peak occurs at nearly the same frequency as the main peak of the former but with strongly increased width (~104 meV FWHM). The result shows that on the average, the H--sites occupied in amorphous and crystalline structure are mainly tetrahedral type holes, but the distribution of local environment for the hydrogen atoms in the alloy glass is much broader because the polyhedra in it may be heavily distorted andthere is local fluctuation in its chemical composition.