School of Materials Science and Engineering, Nanyang Technological University, Blk N4.1, Nanyang Avenue, Singapore 639798.
Dalton Trans. 2010 Jul 28;39(28):6488-95. doi: 10.1039/c001612h. Epub 2010 Jun 15.
The crystal structures of the ferric carbonate-hydroxyapatite (Fe-CHAp) and oxyapatite (Fe-OAp) pseudomorphs were investigated by powder neutron diffraction and Fourier transform infrared spectroscopy. At low iron loadings, Fe-CHAp (x = 0.1) is A-B type carbonate apatite-2H, where atmospheric CO(2) displaces tunnel hydroxyl and framework phosphate (Ca(2+) + 2PO(4)(3-) --> square(Ca) + 2CO(3)(2-) and Ca(2+) + OH(-) --> Fe(3+) + CO(3)(2-)), while Fe-CHAp (x = 0.2) is A type carbonate apatite-2M. For high iron loadings (x = 0.5), near the solubility limit, Fe(3+) incorporation includes concomitant oxidation of hydroxyl groups (Ca(2+) + OH(-) --> Fe(3+) + O(2-)). The discontinuity in the lattice metric at x approximately 0.2 together with a progressive reduction of OH(-) and CO(3)(2-), substantiates these incorporation mechanisms. The general formula of Fe-CHAp is [Ca(4-x)(F)Fe(x)][Ca(6-y)(T) square(y)][(PO(4))(6-y)(CO(3))(y)][(OH(4))(2-x)(CO(3))(x)] (0 < or = x < or = 0.2, 0 < or = y < or = 0.2) and Fe-OAp is [Ca(3.8)(F)Fe(0.2)][Ca(6-x)(T)Fe(x)][(PO(4))][O(0.2+x)(OH)(1.8-x)] (0 < x < or = 0.3). These new data are placed in the context of earlier crystallographic studies, with the Ca(I)O(6) metaprism twist angle (phi) shown to be a reliable indicator of symmetry, such that for phi(max) > 27.(0) degrees, monoclinic and triclinic structures are preferable.
通过粉末中子衍射和傅里叶变换红外光谱研究了碳酸铁-羟磷灰石（Fe-CHAp）和氧磷灰石（Fe-OAp）的假晶结构。在低铁负载下，Fe-CHAp（x = 0.1）为 A-B 型碳酸磷灰石-2H，其中大气 CO₂取代隧道羟基和框架磷酸盐（Ca²⁺ + 2PO₄³⁻ → 方（Ca）+ 2CO₃²⁻和 Ca²⁺ + OH⁻ → Fe³⁺ + CO₃²⁻），而 Fe-CHAp（x = 0.2）为 A 型碳酸磷灰石-2M。对于高铁负载（x = 0.5），接近溶解度极限，Fe³⁺的掺入包括羟基的同时氧化（Ca²⁺ + OH⁻ → Fe³⁺ + O²⁻）。在 x 约为 0.2 时，晶格度量的不连续性以及 OH⁻和 CO₃²⁻的逐渐减少，证实了这些掺入机制。Fe-CHAp 的通式为 [Ca₄-x（F）Fe（x）][Ca₆-y（T）方（y）][（PO₄）₆-y（CO₃）y][（OH₄）2-x（CO₃）x]（0 ≤ x ≤ 0.2，0 ≤ y ≤ 0.2）和 Fe-OAp 为 [Ca₃.8（F）Fe（0.2）][Ca₆-x（T）Fe（x）][（PO₄）][O（0.2 + x）（OH）（1.8 - x）]（0 ＜ x ≤ 0.3）。这些新数据被置于早期晶体学研究的背景下，表明 Ca（I）O₆ 五角棱镜扭曲角（phi）是对称性的可靠指标，因此对于 phi（max）＞27.（0）度，单斜和三斜结构是优选的。
