Substitution of Ca2+ in Calcite by Sn2+ and Sr2+ cations through ion exchange characterized by X-ray absorption and photoelectron spectroscopies
Jonathan B. Junio, Prae Chirawatkul, Marlon T. Conato, Candy C. Mercado
Abstract
Abstract Tin (Sn 2+ ) and strontium (Sr 2+ ), two potential alternatives to lead (Pb 2+ ) in perovskite formation, were explored in transforming calcium carbonate (CaCO 3 ) into a leaving group in a cation exchange reaction. This is the first part of a sequential ion exchange process in transforming calcite into a Pb-free perovskite material for perovskite solar cell applications. Calcite, a polymorph of CaCO 3 , was successfully transformed into strontianite (SrCO 3 ) through a cation exchange reaction. In the Sn substitution reaction on the other hand, no SnCO 3 formation was noted. Instead, oxides of Sn were formed. The wider spaces in between Ca 2+ cations in (100) orientation account for the higher atomic Sn 2+ and Sr 2+ concentrations as compared to (001) orientation, where the cation movement is restricted. X-ray absorption and photoelectron spectroscopies were used to investigate the ion-exchange transformation of calcite towards the formation of an intermediate carbonate material. Graphic abstract