Atomic resolution transmission electron microscopy visualisation of channel occupancy in beryl in different crystallographic directions

IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Physics and Chemistry of Minerals Pub Date : 2024-07-05 DOI:10.1007/s00269-024-01285-6
Carina Silke Hanser, Per Erik Vullum, Antonius Theodorus Johannes van Helvoort, Fabian Dietmar Schmitz, Tobias Häger, Roman Botcharnikov, Bodil Holst
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Abstract

The causes of colour in beryl have been a research topic for decades. For some varieties, such as emerald (green, coloured by Cr3+ and/or V3+), the main cause of colour is substitutions by metal atoms within the framework. However, the causes for the yellow and blue colours in heliodor, golden beryl and aquamarine are still debated. It is generally agreed that Fe ions are responsible for the colour, but there are differing conclusions about the valence states of these ions, the occupied positions and the colour-inducing processes involved. The colour of aquamarine is commonly attributed to intervalence charge transfer (IVCT) between Fe3+ and Fe2+. Various combinations of sites have been proposed to host the Fe ions engaging in this IVCT. Here we present a new approach to address the topic of colour generation: atomic resolution scanning transmission electron microscopy (STEM). For the first time, atomic resolution images of a beryl (natural aquamarine) are presented in the three crystallographic directions [0001], [1-210] and [1-100]. Ions are clearly resolved in the channels. From the ratio of channel occupation and the correlation of the atoms per formula unit (apfu) calculations we conclude that Fe resides in the framework, not in the channels. The projections in the [1-210] direction directly show that the cavity channel site 2a is occupied, most likely by Cs, in agreement with recent results in the literature.

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用原子分辨率透射电子显微镜观察绿柱石在不同晶体学方向上的通道占用情况
几十年来,绿柱石的颜色成因一直是一个研究课题。对于某些品种,如祖母绿(绿色,由 Cr3+ 和/或 V3+ 着色),颜色的主要成因是框架内金属原子的置换。然而,关于氦碘石、金绿柱石和海蓝宝石中黄色和蓝色的成因仍存在争议。人们普遍认为铁离子是造成颜色的原因,但对这些离子的价态、占据的位置和所涉及的致色过程却有不同的结论。海蓝宝的颜色通常归因于 Fe3+ 和 Fe2+ 之间的间隔电荷转移(IVCT)。人们提出了各种不同的位置组合来承载参与这种 IVCT 的铁离子。在此,我们提出了一种解决颜色生成问题的新方法:原子分辨率扫描透射电子显微镜(STEM)。我们首次展示了绿柱石(天然海蓝宝石)在三个晶体学方向 [0001]、[1-210] 和 [1-100] 上的原子分辨率图像。离子在通道中清晰分辨。根据沟道占据率和每式单位(apfu)原子的相关性计算,我们得出结论:铁存在于框架中,而不是沟道中。[1-210]方向上的投影直接表明,空腔通道位点 2a 被占据,很可能是被铯占据,这与最近的文献结果一致。
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来源期刊
Physics and Chemistry of Minerals
Physics and Chemistry of Minerals 地学-材料科学:综合
CiteScore
2.90
自引率
14.30%
发文量
43
审稿时长
3 months
期刊介绍: Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are: -Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.) -General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.) -Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.) -Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.) -Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems -Electron microscopy in support of physical and chemical studies -Computational methods in the study of the structure and properties of minerals -Mineral surfaces (experimental methods, structure and properties)
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