Compositional dependence of infrared absorption spectra of crystalline silicates - I. Mg–Fe pyroxenes
Compositional dependence of infrared absorption spectra of crystalline silicates - I. Mg–Fe pyroxenes
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结晶硅酸盐红外吸收光谱的成分依赖性 - I. Mg-Fe 辉石
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
D. Sakamoto
中科院分区：
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作者：
H. Chihara;C. Koike;A. Tsuchiyama;S. Tachibana;D. Sakamoto
在实验室合成了不同Mg=(Mg+Fe)比例的结晶Mg-Fe辉石(MgSiO3、Mg0:5Fe0:5SiO3和FeSiO3)，并研究了它们在红外区的吸收性能。本工作首次报道了硅铁矿（FeSiO3）的吸收光谱。我们的研究证实，镁端元在远红外区域具有清晰的特征，特别是在该波长范围内很容易区分两种类型的晶体结构（斜方晶系和单斜晶系）。此外，我们发现吸收光谱取决于材料的化学和晶体结构：（1）当铁浓度增加时，镁端元中突出的远红外特征消失。然而，即使在含铁辉石中，中红外特征随铁浓度的变化与远红外特征相比也不太显着。 (2) 峰位置向较长波长移动，铁浓度增加；位移的相关性与波数 (cm 1 ) 近似呈线性。 (3)端元的远红外波段带宽明显小于固溶体的远红外波段带宽。这些结果表明辉石的远红外特征对化学成分和晶体结构非常敏感。因此，远红外特征对于星周辉石的化学成分和晶体结构是非常有用的限制。
Crystalline Mg-Fe pyroxenes with dierent Mg=(Mg+ Fe) ratio (MgSiO3 Mg0:5Fe0:5SiO3 and FeSiO3 )w ere synthesized in laboratory and their absorption properties were investigated in the infrared region. The absorption spectrum of ferrosilite (FeSiO3) is reported for the first time in this work. Our study confirmed that the Mg end members have sharp and characteristic features in the far-IR region and in particular that it is easy to distinguish the two types of crystalline structures (orthorhombic and monoclinic) in this wavelength range. In addition we find that the absorption spectra depend on the chemistry and crystal structure of the material: (1) The far-IR features which are prominent in the Mg end members, vanish when the iron concentration is increased. However, even in the iron bearing pyroxenes, the variation of the mid-IR features with Fe concentration is less significant in comparison to that of the far-IR features. (2) Peak positions shifted to longer wavelength an increase in iron concentration; the dependence of the shift is approximately linear in wavenumber (cm 1 ). (3) Bandwidths of the far-IR bands for the end members are significantly smaller than those of solid solutions. These results suggest that the far-IR features of pyroxenes are very sensitive to chemical composition and crystal structure. Therefore, far-IR features are a very useful constraint on the chemical composition and crystal structure of circumstellar pyroxenes.