Tin (Sn²⁺) and strontium (Sr²⁺) are potential replacements to lead (Pb²⁺) in perovskite synthesis since Sn is on the same IVA group in the periodic table as Pb while Sr is a promising alternative according to Goldschmidt’s rules and quantum mechanical analysis. The crystal radii of their ions are also nearly identical with Pb²⁺=1.33 Å, Sn²⁺=1.36 Å, and Sr²⁺=1.32 Å. In this study, both Sn and Sr were explored in transforming calcite, a polymorph of calcium carbonate (CaCO₃) into a leaving group in the first step of a sequential ion-exchange reaction towards perovskite formation. Instead of forming the intermediate tin carbonate (SnCO₃), the reaction resulted in the formation of gypsum or calcium sulfate dihydrate (CaSO_4.2H₂O) and Sn in the form of oxides. These oxides, however, are useful especially when these are in the form of tin dioxide-coated CaCO₃ shell-core structures—having demonstrated flame retardant and smoke suppressant properties. On the other hand, calcite was successfully transformed into strontium carbonate (SrCO₃) or strontianite through the cation exchange reaction. X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) were used to observe the resulting materials and understand the transformation of both Placuna placenta (or Capiz) shells and single-crystal calcite from the ion-exchange reactions.

锡 (Sn ²⁺ ) 和锶 (Sr ²⁺ ) 是钙钛矿合成中铅 (Pb ²⁺ ) 的潜在替代品，因为 Sn 在元素周期表中与 Pb 在同一个 IVA 族，而根据 Goldschmidt 规则，Sr 是一种很有前途的替代品和量子力学分析。它们的离子的晶体半径也与 Pb ²⁺ =1.33 Å、Sn ²⁺ =1.36 Å 和 Sr ²⁺ =1.32 Å几乎相同。在这项研究中，在向钙钛矿形成的顺序离子交换反应的第一步中，探索了 Sn 和 Sr 将方解石（一种碳酸钙 (CaCO ₃ )的多晶型物）转化为离去基团。而不是形成中间体碳酸锡（SnCO ₃)，反应导致形成石膏或硫酸钙二水合物 (CaSO _4. 2H ₂ O) 和氧化物形式的 Sn。然而，当这些氧化物呈二氧化锡涂覆的 CaCO ₃壳核结构的形式时尤其有用——已证明具有阻燃和抑烟性能。另一方面，方解石通过阳离子交换反应成功转化为碳酸锶（SrCO ₃）或菱锶矿。X 射线衍射 (XRD) 和 X 射线光电子能谱 (XPS) 用于观察所得材料并了解来自离子交换反应的Placuna 胎盘（或 Capiz）壳和单晶方解石的转变。