Crystallographic mechanism of the elastic behaviour of synthetic bütschliite K2Ca(CO3)2 on compression to 20 GPa

IF 1.2 4区地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY

Physics and Chemistry of Minerals Pub Date : 2024-07-28 DOI:10.1007/s00269-024-01291-8

Anna Yu. Likhacheva, Alexandr V. Romanenko, Sergey V. Rashchenko, Sofija Miloš, Paolo Lotti, Ronald Miletich, Anton Shatskiy

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Abstract

Bütschliite, K₂Ca(CO₃)₂, occurring as inclusions in mantle minerals, is regarded as one of the key phases to understand phase relationships of dense potassium carbonates and thus to evaluate their potential role within the Earth’s deep carbon cycle. Accordingly, the high-pressure behavior of synthetic bütschliite has been investigated by in-situ single-crystal X-ray diffraction under isothermal compression up to 20 GPa at T = 298 K. The compression mechanism before and after the trigonal-to-monoclinic (R-3m to C2/m) phase transition at ∼6 GPa, found previously, is characterized in terms of the evolution of the cation polyhedra and carbonate groups. On this basis, the modulation of the axial compression is interpreted, and the contribution of the cation polyhedra into the bulk compression is estimated. The refined compressibility of the monoclinic phase (K₀ = 44(2) GPa) fits to the trend of the carbonate bulk modulus versus average non-carbon cation radius. The analysis of the obtained and literature structural data suggests the distortion of a large cation polyhedron to be an effective tool to strengthen the carbonate structure at high pressure. On the other hand, the observed symmetrization of the cation polyhedra in trigonal bütschliite is apparently a crucial factor of its stabilization at high pressure upon the temperature rise observed previously. The structural crystallography provided in this study supports the enhanced stability of trigonal bütschliite at high P, T conditions and its significance of being considered as a constituent of the inclusions in deep minerals.

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压缩至 20 GPa 时合成菱镁矿 K2Ca(CO3)2 弹性行为的晶体学机制

作为地幔矿物中的包裹体出现的黑钾石（K2Ca(CO3)2）被认为是了解致密碳酸钾相关系并进而评估其在地球深层碳循环中潜在作用的关键相位之一。因此，我们通过原位单晶 X 射线衍射研究了合成黑钾盐在 20 GPa 等温压缩（T = 298 K）条件下的高压行为。我们从阳离子多面体和碳酸酯基团的演化来描述了之前发现的在 6 GPa ∼时三方到单斜（R-3m 到 C2/m）相变前后的压缩机制。在此基础上，对轴向压缩的调制进行了解释，并估算了阳离子多面体对体积压缩的贡献。单斜相（K0 = 44(2) GPa）的细化压缩性与碳酸盐体积模量与非碳阳离子平均半径的趋势相吻合。对获得的结构数据和文献数据的分析表明，大阳离子多面体的变形是在高压下强化碳酸盐结构的有效工具。另一方面，所观察到的三方绿柱石中阳离子多面体的对称性显然是其在高压下稳定的关键因素，而这正是之前所观察到的温度升高的原因。本研究提供的结构晶体学支持了三方菱锰矿在高P、高T条件下稳定性的增强，以及将其视为深矿物中包裹体成分的重要意义。

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来源期刊

Physics and Chemistry of Minerals 地学-材料科学：综合

CiteScore

2.90

自引率

14.30%

发文量

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)