Single crystals of SFCA-II with composition Ca 2.46 Fe 3+ 8.57 Fe 2+ 0.52 Al 5.45 O 24 have been obtained from synthesis experiments in the temperature range between 1300 and 1200 °C. Diffraction experiments at ambient conditions yielded the following basic crystallographic data: space group P 1 ¯ $$ \overline{1} $$ , a = 10.3016(4) Å, b = 10.4656(4) Å, c = 17.9553(6) Å, α = 90.062(3), β = 89.977(3)°, γ = 109.510(3)°, V = 1824.66(12) Å 3 , Z = 4. Structure determination and subsequent least-squares refinements resulted in a residual of R(|F|) = 0.0349 for 7406 independent reflections and 773 parameters. Site occupancy refinements on the 35 octahedral (M) and tetrahedral (T) positions in the asymmetric unit were aided by crystallochemical considerations and the assumption of charge balance between the cations and anions. The derived formula compares well with the outcome of electron microprobe studies. The crystal structure of SFCA-II shows the typical features of the SFCA-family. It can be built from an alternating sequence of two different types of fundamental layers. For SFCA-II, they are oriented parallel to (100). Layer-type I is solely based on [MO 6 ]-octahedra (M: Ca, Fe 3+ , Al) forming individual five polyhedra wide bands. Within a single band, the octahedra share common edges. Layer-type II, on the other hand, contains [MO 6 ]-octahedra as well as [TO 4 ]-tetrahedra (T: Al, Fe 3+ , Fe 2+ ). By corner sharing each [MO 6 ]-group is linked to two adjacent tetrahedra into [MT 2 O 12 ]-clusters or “winged octahedra”. Linkage between neighboring strips of these moieties is provided by additional [TO 4 ]-tetrahedra arranged in vierer single-chains. Our investigation rectifies previous studies on SFCA-II where wrong atomic coordinates have been published.

中文翻译：

---

SFCA-II 型 Ca2.46Fe3+8.57 Fe2+0.52Al5.45O24 – 铁矿石烧结相的改进结构模型

在 1300 至 1200 °C 的温度范围内，从合成实验中获得了组成为 Ca 2.46 Fe 3+ 8.57 Fe 2+ 0.52 Al 5.45 O 24 的 SFCA-II 单晶。环境条件下的衍射实验产生以下基本晶体学数据：空间群 P 1¯ $$ \overline{1} $$ , a = 10.3016(4) Å, b = 10.4656(4) Å, c = 17.9553(6) Å , α = 90.062(3), β = 89.977(3)°, γ = 109.510(3)°, V = 1824.66(12) Å 3 , Z = 4. 结构确定和随后的最小二乘精修导致残差为对于 7406 个独立反射和 773 个参数，R(|F|) = 0.0349。晶体化学方面的考虑以及阳离子和阴离子之间的电荷平衡假设有助于对不对称单元中 35 个八面体 (M) 和四面体 (T) 位置的位点占有率进行改进。推导出的公式与电子微探针研究的结果很好地进行了比较。SFCA-II 的晶体结构显示了 SFCA 家族的典型特征。它可以由两种不同类型的基本层的交替序列构建。对于 SFCA-II，它们平行于 (100)。层类型 I 仅基于 [MO 6 ]-八面体 (M: Ca, Fe 3+ , Al) 形成单独的五个多面体宽带。在单个带内，八面体共享公共边。另一方面，层类型 II 包含 [MO 6 ]-八面体以及 [TO 4 ]-四面体（T：Al、Fe 3+ 、Fe 2+ ）。通过角共享，每个 [MO 6 ]-组与两个相邻的四面体连接成 [MT 2 O 12 ]-簇或“带翼八面体”。这些部分的相邻条带之间的连接由排列在维耶尔单链中的额外[TO 4 ]-四面体提供。