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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Electron Density and Optical Anisotropy in Rhombohedral Carbonates. III. Synchrotron X-ray Studies of CaCO_3, MgCO_3 and MnCO_3
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Electron Density and Optical Anisotropy in Rhombohedral Carbonates. III. Synchrotron X-ray Studies of CaCO_3, MgCO_3 and MnCO_3

机译：菱面体碳酸盐中的电子密度和光学各向异性。三， CaCO_3，MgCO_3和MnCO_3的同步辐射X射线研究

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摘要

Diffraction-deformation electron-density (Ap) images for small, naturally faced single crystals of synthetic calcite (CaCO3), magnesite (MgCO3) and mineral rhodochrosite (MnCO3) were measured with focused A = 0.7 and 0.9 A synchrotron (SR) X-radiation. Mo Ka (A = 0.71073 A) structure factors were also measured for MnCO3. Lattice mode frequencies predicted from eigenvalues of T and L tensors for CO3 rigid-group motion in these structures are close to spectroscopic values. High approximate Ap symmetry around the cations increases towards 6/mmm in the sequence CaCO3, MgCO3 to MnCO3. The Ap topography near the CO3 groups shows the influence of the cations, and correlates strongly with the refractive indices, as required for a cause and effect relationship between electron density and optical anisotropy. Aspherical electron density around the Mn atom can be attributed to the effect of a non-ideal octahedral crystal field on the 3d electron distribution. The relationship of the Ap topography near the Mn atom with that near the CO3 group in MnC03 is consistent with magnetic interactions. Space group R3c, hexagonal, Z = 6, T= 295 K: CaCO3, Mr = 100.09, a = 4.988(2), c = 17.068(2)A, V = 367.8(3)A3, Dx = 2.711 MgrrT3, IiO7 = 1.93 mm~(-1), F(000) = 300, R = 0.015, wR = 0.012, S = 3.0 for 437 unique reflections; MgCO3, Mr = 84.31, a = 4.632(1), c = 15.007 (2) A, V = 278.8 (2) A3, Dx = 3.013 Mgmf3, M_(0.9_ = 0.99 mm~(-1), F(000) = 252, R = 0.015, wR = 0.021, S = 4.34 for 270 unique reflections; MnCO_3, Mr = 114.95, a = 4.772(3), c = 15.637 (3) A, V = 308.4(4) A3, Dx = 3.713 Mgm~(-3), I_(0.7) = 5.62 mm~(-1), F(000) = 330, R = 0.015, wR = 0.039, S = 3.38 for 386 unique reflections of the SR data set and a = 4.773 (1), c= 15.642(1) A, V =308.6(1) A3, Dx = 3.71 IMgnT3, li(MoKa) = 5.86 mm~(-1), R = 0.017, wR = 0.024, S = 2.79 for 368 unique Mo Ka reflections.
机译：用聚焦的A = 0.7和0.9 A同步加速器（SR）X-测量了天然小方晶的方解石（CaCO3），菱镁矿（MgCO3）和矿物菱锰矿（MnCO3）的衍射-形变电子密度（Ap）图像。辐射。还测量了Mn Ka3的Mo Ka（A = 0.71073 A）结构因子。根据这些结构中CO3刚性基团运动的T和L张量特征值预测的晶格模式频率接近光谱值。阳离子周围的高近似Ap对称性按CaCO3，MgCO3至MnCO3的顺序增加至6 / mm。靠近CO3基团的Ap形貌显示了阳离子的影响，并且与折射率紧密相关，这是电子密度与光学各向异性之间因果关系所需的。 Mn原子周围的非球面电子密度可归因于非理想八面体晶体场对3d电子分布的影响。 MnCO 3中靠近Mn原子的Ap形貌与靠近CO 3基的Ap形貌的关系与磁相互作用一致。空间组R3c，六边形，Z = 6，T = 295 K：CaCO3，Mr = 100.09，a = 4.988（2），c = 17.068（2）A，V = 367.8（3）A3，Dx = 2.711 MgrrT3，IiO7 = 1.93 mm〜（-1），F（000）= 300，R = 0.015，wR = 0.012，S = 3.0对于437次独特反射; MgCO3，Mr = 84.31，a = 4.632（1），c = 15.007（2）A，V = 278.8（2）A3，Dx = 3.013 Mgmf3，M_（0.9_ = 0.99 mm〜（-1），F（000） ）= 252，R = 0.015，wR = 0.021，S = 4.34对于270次独特反射; MnCO_3，Mr = 114.95，a = 4.772（3），c = 15.637（3）A，V = 308.4（4）A3，Dx对于SR数据集的386次唯一反射，I =（3.73 Mgm〜（-3），I_（0.7）= 5.62 mm〜（-1），F（000）= 330，R = 0.015，wR = 0.039，S = 3.38 a = 4.773（1），c = 15.642（1）A，V = 308.6（1）A3，Dx = 3.71 IMgnT3，li（MoKa）= 5.86 mm〜（-1），R = 0.017，wR = 0.024，S 368个独特的莫卡反射= 2.79。

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