Effects of Fe ↔ Al substitution on triclinic SFCA-I-type compounds with general formula A₄₀O₅₆ (A: Ca, Al, Fe³⁺, Fe²⁺) have been studied using single-crystal X-ray diffraction. Crystals of sufficient quality and size were synthesized in the temperature range between 1200 and 1300 °C. Six samples with Al/Fe_Tot ratios of 0.127, 0.173, 0.216, 0.310, 0.349 and 0.459 have been structurally characterized. SFCA-I can be described with a modular approach involving the stacking sequence < PSS > of “P” and “S” modules that can be imagined as being cut from the well-known pyroxene (P) and spinel (S) structure types. Furthermore, SFCA-I is related to the sapphirine supergroup of minerals. Within the present solid-solution series, the contents in calcium show only minor variations (≈ 6.7 a.p.f.u.). The twenty crystallographically independent tetrahedrally (T) and octahedrally (M) coordinated cation sites exhibit considerable differences concerning the Al uptake. Indeed, Al is preferentially incorporated into the tetrahedra belonging to the single-chains located in the pyroxene modules. Ferrous iron, on the other hand, is restricted to one of the T-positions within the spinel blocks. Most structural aspects from unit-cell parameters and cell volumes to site occupancies, tetrahedral chain kinking as well as polyhedral distortions are defined by linear or nearly linear trends when plotted against the Al/Fe_Tot ratio. Analysis of the < T–O > and < M–O > distances showed a complex interplay between the different coordination polyhedra resulting in a contrasting behavior of these values with positive or negative change rates as a function of composition. Evaluation of the average chemical strain tensor derived from the sets of lattice parameters for the two samples of the abovementioned series showing the highest and lowest Al/Fe_Tot ratios indicated, that the major contraction with increasing Al content is perpendicular to the pyroxene- and spinel modules. Furthermore, the pyroxene module seems to be more affected when compared with the spinel block. There is evidence that the SFCA-I-type solid-solution series is limited on both the Al- and Fe-rich sides. The present investigation provides—for the first time—a detailed crystallographic analysis on the impact of chemical variations on a compound that is of relevance to the field of applied mineralogy related to the technologically important process of iron-ore sintering.

已经使用单晶 X 射线衍射研究了 Fe ↔ Al 取代对通式 A ₄₀ O ₅₆ (A: Ca, Al, Fe ³⁺ , Fe ²⁺ ) 的三斜 SFCA-I 型化合物的影响。在 1200 至 1300 °C 的温度范围内合成了足够质量和尺寸的晶体。_含铝/铁_{Tot 的}六个样品0.127、0.173、0.216、0.310、0.349和0.459的比率已在结构上表征。SFCA-I 可以用模块化方法来描述，包括“P”和“S”模块的堆叠序列 < PSS >，可以想象这些模块是从众所周知的辉石 (P) 和尖晶石 (S) 结构类型中切割出来的。此外，SFCA-I 与矿物的蓝宝石超群有关。在目前的固溶体系列中，钙的含量只有很小的变化 (≈ 6.7 apfu)。二十个晶体学独立的四面体 (T) 和八面体 (M) 配位阳离子位点在铝吸收方面表现出相当大的差异。事实上，Al 优先被纳入属于位于辉石模块中的单链的四面体。另一方面，亚铁，仅限于尖晶石块内的 T 位置之一。从晶胞参数和单元体积到位点占有率、四面体链扭结以及多面体扭曲的大多数结构方面都由线性或近线性趋势定义，当与 Al/Fe 作图时_总比率。< T-O > 和 < M-O > 距离的分析表明，不同配位多面体之间存在复杂的相互作用，导致这些值的对比行为具有正或负变化率作为组成的函数。从上述系列的两个样品的晶格参数组得出的平均化学应变张量的评估显示出最高和最低的 Al/Fe _Tot比率表明，随着铝含量增加，主要收缩垂直于辉石和尖晶石模块。此外，与尖晶石块相比，辉石模块似乎受到的影响更大。有证据表明 SFCA-I 型固溶体系列在富铝和富铁侧均受到限制。本研究首次提供了关于化学变化对化合物影响的详细晶体学分析，该分析与与铁矿石烧结技术重要过程相关的应用矿物学领域相关。