Geometrical parameterization of the crystal chemistry of P63/m apatites:: comparison with experimental data and ab initio results
Geometrical parameterization of the crystal chemistry of P63/m apatites:: comparison with experimental data and ab initio results
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DOI：
10.1107/s0108768105031125
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发表时间：
2005-12-01
影响因子：
1.9
通讯作者：
White, TJ
中科院分区：
文献类型：
--
作者：
Mercier, PHJ;Le Page, Y;White, TJ
用几何晶体化学模型对18个已发表的全有序P6（3）/m（A（4）（I））（A（6）（II））（BO 4）（6）X-2磷灰石端元组成进行了结构优化和从头计算。精确到+/- 0.025埃，c的大小是从表征... - A（II）-O3-B-O3-A（II）-.原子，而a的是从描述（A（I）O（6））-（BO 4）多面体排列的那些确定的。使用基于几何晶体化学模型预测的多变量函数，c/a比可预测为+/- 0.2%，但不能归因于单个晶体化学参数的调整。代数独立的晶体化学参数之间观察到的相关性，代表主要观察到的多面体扭曲揭示他们作为最小能量的解决方案，以适应这种灵活的结构类型内的失配组件。对于给定的组成的材料，从头计算晶体化学参数的良好协议（在+/- 0.5-2.0%），观察到只有那些从单晶细化与R 4.0%是不好的，而分散从Rietveld细化是相当大的。因此，在此报告了以下待实验工作的组分的从头算晶胞数据、原子坐标和晶体化学参数：（Zn，Hg）（10）（PO_4）（6）（Cl，F）（2），（Ca，Cd）（10）（VO_4）（6）Cl-2和（Ca，Pb，Cd）（10）（CrO_4）（6）Cl-2。
Experimental structure refinements and ab initio simulation results for 18 published, fully ordered P6(3)/m (A(4)(I))(A(6)(II))(BO4)(6)X-2 apatite end-member compositions have been analyzed in terms of a geometric crystal-chemical model that allows the prediction of unit-cell parameters (a and c) and all atom coordinates. To an accuracy of +/- 0.025 angstrom, the magnitude of c was reproduced from crystal-chemical parameters characterizing chains of ...-A(II)-O3-B-O3-A(II)-... atoms, whereas that of a was determined from those describing (A(I)O(6))-(BO4) polyhedral arrangements. The c/a ratio could be predicted to +/- 0.2% using multi-variable functions based on geometric crystal-chemical model predictions, but could not be ascribed to the adjustment of a single crystal-chemical parameter. The correlations observed between algebraically independent crystal-chemical parameters representing the main observed polyhedral distortions reveal them as the minimum-energy solution to accommodate misfit components within this flexible structure type. For materials with given composition, good agreement (within +/- 0.5-2.0%) of ab initio crystal-chemical parameters was observed with only those from single-crystal refinements with R 4.0% was not as good, while the scatter with those from Rietveld refinements was considerable. Accordingly, ab initio cell data, atomic coordinates and crystal-chemical parameters were reported here for the following compositions awaiting experimental work: (Zn,Hg)(10)(PO4)(6)(Cl,F)(2), (Ca,Cd)(10)(VO4)(6)Cl-2 and (Ca,Pb,Cd)(10)(CrO4)(6)Cl-2.