Potassium incorporation in the structure of combeite has been studied in detail. Since natural combeites are known to contain only small amounts of potassium focus was laid on the Na-rich part of a hypothetical solid-solution series with composition Na_2-xK_xCa₂Si₃O₉. Samples were prepared from mixtures of silica and the corresponding carbonates for nominal compositions with x = 0.2, 0.3 and 0.5, heated from ambient temperature to 1350 °C and slowly cooled to 1000 °C. After disintegration of the carbonates, the platinum capsules used as sample containers were welded shut in order to avoid losses of the volatile K₂O and Na₂O components. From all three batches potassium containing combeite crystals could be retrieved. Single-crystal diffraction experiments revealed the following compositions: Na_2.10(1)K_0.11(1)Ca_1.90(1)Si₃O₉, Na_2.09(1)K_0.18(1)Ca_1.91(1)Si₃O₉ and Na_2.13(1)K_0.18(1)Ca_1.87(1)Si₃O₉. Consistently, the trigonal crystals (space group P 3₁ 2 1) contained (i) (K + Na):Ca ratios larger than 1:1 and (ii) potassium concentrations lower than those in the starting mixtures. Since the K-contents of the samples obtained from the runs with x = 0.3 and 0.5 were almost identical, the solid-solution seems to be rather limited with an upper boundary of about one potassium atom per unit cell. The structure of the K-containing combeites is very close to the K-free structures reported in the literature. It can be described as a mixed tetrahedral-octahedral network in which additional K, Na and Ca cations are incorporated for charge compensation. A detailed analysis of the topological features of the net is presented. From the six observed extra-framework sites only the M22 position showing a coordination environment with ten next oxygen neighbours is involved in the K-substitution. Potassium uptake is also reflected in increasing values for the lattice parameters a and c as well as the unit-cell volumes. Actually, the c-axis is more affected from the incorporation of the comparatively large K⁺-cations.

已经详细研究了复合镁石结构中钾的掺入。由于已知天然复合沸石仅含有少量钾，因此将重点放在假设固溶体系列的富钠部分，其组成为 Na _2-x K _x Ca ₂ Si ₃ O ₉。样品由二氧化硅和相应碳酸盐的混合物制备，标称组成为 x = 0.2、0.3 和 0.5，从环境温度加热至 1350 °C，然后缓慢冷却至 1000 °C。碳酸盐分解后，将用作样品容器的铂胶囊焊接起来，以避免挥发性 K ₂ O 和 Na _2的损失O 组件。从所有三个批次中都可以回收含钾的 Combeite 晶体。单晶衍射实验揭示了以下组成：Na _2.10(1) K _0.11(1) Ca _1.90(1) Si ₃ O ₉、Na _2.09(1) K _0.18(1) Ca _1.91(1) Si ₃ O ₉和Na _2.13(1) K _0.18(1) Ca _1.87(1) Si ₃ O ₉。一致地，三角晶体（空间群P 3 ₁2 1) 包含 (i) (K + Na):Ca 比率大于 1:1 和 (ii) 钾浓度低于起始混合物中的钾浓度。由于从 x = 0.3 和 0.5 的运行中获得的样品的 K 含量几乎相同，因此固溶体似乎相当有限，每个晶胞的上限约为一个钾原子。含钾复合体的结构与文献中报道的无钾结构非常接近。它可以被描述为一个混合的四面体-八面体网络，其中加入了额外的 K、Na 和 Ca 阳离子用于电荷补偿。详细分析了网络的拓扑特征。从六个观察到的框架外位点中，只有 M22 位置显示与十个下一个氧邻居的协调环境参与了 K 取代。a和c以及晶胞体积。实际上，c轴受相对较大的 K ⁺阳离子的影响更大。