Abstract The O–H stretching vibration mode in crystals of (Mn,Cl)-rich and F-poor minerals of the apatite-supergroup has been studied by micro-Raman spectroscopy. The main purpose was to check if such an analysis can provide a quick and simple method to assess the distribution of Ca and Mn together with traces of Fe + Mg ( = Mn*) on nonequivalent cationic sites in the apatite structure, especially in small and strongly heterogeneous crystals directly in thin sections. The O–H stretching vibration mode can then be treated as a useful structural probe giving information on the M2 occupants bonded to XOH. Pieczkaite, with the empirical formula (Mn4.49Fe0.47Ca0.05Mg0.01)Σ5.01P2.99O12[Cl0.83(OH)0.17], displays the O–H stretching mode centered at ~3380 cm–1, which shows that the complete replacement of Ca by Mn* at the M2 site is connected with a shift of the O–H stretching band ~192 cm–1 toward lower wavenumbers in relation to the O–H Raman band position reported for hydroxylapatite. The value is high enough to be an indicator of the M2Mn*···OH content in any sample of Mn-enriched apatite. Studies of the fine structure of the band disclosed its dependence on (1) the local combinations of Ca and Mn* forming triplets of M2 cations bonded to the X anion, (2) the presence of OH+Cl at the two half-occupied X sites that form chemical bonds with the M2 cations varying in strength and length, and (3) the spatial geometry of the X–M2 bonds and polarizability of the monovalent X anion by varying cations in the M2M2M2 triplets. The deconvolution of the band into maximum eight component bands with constant Raman shifts opens the possibility of evaluating the averaged M2M2M2 triplet bonded to oxygen of the XOH group. If the OH/ (OH+Cl) fraction is known, the amounts of Ca and Mn* bonded to XOH can also be estimated. Application of the method to the holotype parafiniukite showed a slightly diferent distribution of Ca in M2M2M2 triplets than had been assumed from single-crystal X‑ray diffraction. However, it corroborates suggestions that in the apatite structure there may be a preference for M2Ca to be bonded to XOH and M2Mn* to XCl. Our results show that the proposed method can be used as an independent tool in structural studies of Mn-rich minerals of the apatite-supergroup, providing results complementary to single-crystal X‑ray diffraction. This method can easily be adjusted to modern apatite-type nanomaterials synthesized for biomedical and various industrial applications.

中文翻译：

---

富锰磷灰石中 O-H 伸缩振动的拉曼光谱研究：一种结构方法 富锰磷灰石中 O-H 伸缩振动的拉曼光谱研究

摘要 利用显微拉曼光谱研究了磷灰石超群中富 (Mn,Cl) 和贫 F 矿物晶体中的 O-H 伸缩振动模式。主要目的是检查这种分析是否可以提供一种快速简单的方法来评估 Ca 和 Mn 以及痕量 Fe + Mg (= Mn*) 在磷灰石结构中的非等价阳离子位点上的分布，尤其是在小和直接在薄片中形成强异质晶体。然后可以将 O-H 伸缩振动模式视为有用的结构探针，提供有关与 XOH 结合的 M2 乘员的信息。Pieczkaite 的经验公式为 (Mn4.49Fe0.47Ca0.05Mg0.01)Σ5.01P2.99O12[Cl0.83(OH)0.17]，显示以~3380 cm-1 为中心的 O-H 拉伸模式，这表明 M2 位点处的 Ca 被 Mn* 完全取代与 O-H 伸缩带 ~192 cm-1 向较低波数的移动有关，相对于报道的羟基磷灰石的 O-H 拉曼带位置。该值足够高，可以作为任何富锰磷灰石样品中 M2Mn*……OH 含量的指标。对带精细结构的研究揭示了它依赖于 (1) Ca 和 Mn* 的局部组合，形成与 X 阴离子键合的 M2 阳离子的三联体，(2) 在两个半占据的 X 处存在 OH+Cl与强度和长度不同的 M2 阳离子形成化学键的位点，以及 (3) X-M2 键的空间几何形状和通过 M2M2M2 三联体中不同阳离子的单价 X 阴离子的极化率。带解卷积为具有恒定拉曼位移的最多八个分量带打开了评估与 XOH 基团的氧键合的平均 M2M2M2 三重态的可能性。如果 OH/(OH+Cl) 分数已知，则还可以估计与 XOH 结合的 Ca 和 Mn* 的量。将该方法应用于正模parafiniukite 显示M2M2M2 三重态中Ca 的分布与单晶X 射线衍射假设的略有不同。然而，它证实了在磷灰石结构中可能更倾向于将 M2Ca 键合到 XOH 和 M2Mn* 键合到 XCl。我们的结果表明，所提出的方法可以用作磷灰石超群富锰矿物结构研究的独立工具，提供与单晶 X 射线衍射互补的结果。