The Crystal Chemistry of Fe3+ in Nontronite: Implications for Paleoenvironmental Evolution on Mars

We synthesized a series of samples with varying Si/Al/Fe molar ratios under controlled hydrothermal conditions. The resulting solid products were characterized using powder X-ray diffraction, infrared spectroscopy, electron microscopy, and Mössbauer spectroscopy, to elucidate structural characteristics of nontronite. X-ray diffraction (XRD) data shows changed crystallinity of these synthesized samples. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) data illustrated the different morphology and microstructure of samples. Mid infrared spectroscopy (MIR) and Visible-shortwave infrared reflectance (VSWIR) showed change of characteristic vibrations of samples, including band shift and band depth. Mössbauer spectra data identified and quantified the coordination of Fe3+ cations in these samples, including tetrahedral Fe3+ and octahedral Fe3+.

本研究在可控水热条件下，合成了一系列硅/铝/铁摩尔比各异的样品。采用粉末X射线衍射、红外光谱、电子显微镜及穆斯堡尔谱学（Mössbauer spectroscopy）对所得固体产物进行表征，以阐明绿脱石的结构特征。粉末X射线衍射（X-ray diffraction, XRD）测试数据显示，所合成样品的结晶度发生了变化。扫描电子显微镜（Scanning electron microscopy, SEM）与透射电子显微镜（Transmission electron microscopy, TEM）表征结果揭示了各样品的形貌与微观结构差异。中红外光谱（Mid infrared spectroscopy, MIR）与可见-短波红外反射光谱（Visible-shortwave infrared reflectance, VSWIR）测试结果表明，样品的特征振动存在变化，包括谱带偏移与谱带深度改变。穆斯堡尔谱数据鉴定并定量了各样品中三价铁阳离子（Fe³+）的配位状态，涵盖四面体配位Fe³+与八面体配位Fe³+。