Collaborative Research: Investigation of Anion Incompatibility in the Ca10(PO4)6(OH,F,Cl)2 Apatite Atomic Arrangement

磷灰石，Ca10(PO4)6(OH，F，Cl)2，是地球上第十种最丰富的矿物，在地质学、材料科学、医学、牙科、污染物缓解以及作为地球磷循环的基础上具有重要的基础作用；事实上，人体的所有硬组织都是由磷灰石组成的，除了内耳的一小部分。所有这些磷灰石的应用都需要了解矿物的原子排列。尽管关于磷灰石晶体化学的多学科文献很多，但(OH，F，Cl)二元和三元系统成员的原子排列还不是很清楚，我们目前的知识充满了必须解决的不一致；磷灰石是一种稀有的矿物，其固溶体的原子排列不能由端元排列来预测。例如，端元原子排列的混合表明，该系统的二元成员必须经历对称性破坏，具有不混溶的间隙，用未知的电荷平衡方法结合基本空位，和/或具有目前未被认识的阴离子位置。这项多方面的研究将把矿物合成和详细的成分表征与单晶X射线结构分析和魔角旋转核磁共振波谱研究相结合，以阐明羟基、氟、氯三元磷灰石之间的固溶体性质，并提供对阴离子取代和相行为的更好的基础了解。这项研究的结果将在地质学、材料科学、医学和牙科等领域得到应用。概念验证研究表明，沿F-Cl连接的混溶是通过在F-Cl阴离子柱中创建至少四个阴离子中心来实现的，并证实了所提出的合成和分析方法的有效性。

Apatite, Ca10(PO4)6(OH,F,Cl)2, is the tenth most abundant mineral on Earth and one with fundamental importance in geology, materials science, medicine, dentistry, pollutant mitigation, and as the foundation of the Earth's phosphorus cycle; indeed, all hard tissue of the human body except small parts of the inner ear are made of apatite. All of these applications of apatite require understanding of the atomic arrangement of the mineral. Despite the extensive multidisciplinary literature on apatite crystal chemistry, the atomic arrangements of members of the (OH,F,Cl) binary and ternary systems are not well understood and our current knowledge is full of inconsistencies that must be resolved; apatite is one of the rare minerals for which the atomic arrangement of the solid solutions cannot be predicted from the end-member arrangements.Mixing of the end-member atomic arrangements suggests, for example, that binary members of the system must undergo symmetry breaking, possess immiscibility gaps, incorporate essential vacancies with an unknown method of charge balance, and/or possess anion positions that are not currently recognized. This multi-faceted proposed study will couple mineral synthesis and detailed compositional characterization with single-crystal X-ray structure analysis and Magic-Angle-Spinning Nuclear Magnetic Resonance spectroscopic studies in order to elucidate the nature of solid solution among and between the OH, F, Cl ternary apatites, and provide a better fundamental understanding of anionic substitution and phase behavior. The results of this study will have applications in the fields of geology, materials science, medicine, and dentistry. A proof-of-concept study demonstrates that miscibility along the F-Cl join is achieved by the creation of at least four anion sites in the F-Cl anion column, and confirms the efficacy of the proposed synthesis and analysis methods.