Shanrong Zhang, Wen Liang, Mengzeng Wu, Qifa Zhong, Dawei Fan
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引用次数: 0
Abstract
To investigate the quantitative relationship between the crystal structure and composition of Mn-bearing calcite, the solid solutions of Ca1–xMnxCO3 (x = 0.1, 0.3, 0.5, 0.7, 0.9) with continuous MnCO3 mol% content were synthesized at 1 GPa and 700 °C using high-purity CaCO3 and MnCO3 powders as starting materials. The run products were analysized by electron probe, powder X-ray diffraction and Raman spectroscopy. The CaO wt% and MnO wt% of the resulting products are consistent with the expected compositions. The powder X-ray diffraction results show that the products are single phase without any impurities. All diffraction peaks of samples with varying MnCO3 mol% contents can be indexed by the calcite-type structure carbonates ACO3 (R-3c space group; A is a divalent cation), confirming the previous results that there is the completely continuous solid solution between CaCO3 and MnCO3 end members. The unit-cell parameters and volumes of the solid solutions decrease as the MnCO3 mol% content increases, presenting a linear relationship of Ca–Mn ideal miscibility, which is perfectly consistent with the rigid body model of A-site substitution in ACO3. Besides, as MnCO3 mol% content increases, the bond distance of A–O decreases linearly, while the bond distance of C–O changes like a parabola. Therefore, the addition of Mn makes the bond distance of A–O shorten, resulting in the decrease of unit-cell parameters and volumes for Ca1–xMnxCO3. Furthermore, two exterior vibrations (T and L) of the crystal lattice and two internal vibrations (ν4 and ν1) within the CO32− unit are assigned in the Raman spectra of these solid solutions. The characteristic vibration modes T, L, and ν4 as a whole increase with the increasing of MnCO3 mol% content, whereas the characteristic vibration mode ν1 as a whole decreases with the increase of MnCO3 mol% content. These variations in Raman vibration modes are related to the radius of substituted ions.
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)