Active Control of Crystal Nucleation and Growth Using Operando X-ray Imaging

Abstract

The study and utility of novel functional materials are contingent upon obtaining large crystals, which are often grown by non-replicable, slow, and costly traditional methods. In principle, larger crystals can be obtained simply by limiting nucleation while allowing the steady growth of the existing crystals. This can be achieved in aqueous solutions by monitoring crystal formation and growth while controlling the temperature. Modern laboratory X-ray imaging provides a platform for observing crystallization with a wide field of view while being subjected to external stimuli, such as temperature changes, under real synthesis conditions. X-ray tomography has historically focused on passively monitoring and investigating the crystal growth of inorganic materials, without direct interference in the crystallization process. In this study, we utilize X-ray radiography to simultaneously monitor and actively control the crystallization process, thereby achieving rapid growth of large crystals and providing a full view of the process. Crystallization is controlled by hot-stage temperature regulation to prevent and redissolve smaller crystallites, yielding large crystals within short periods of time. As a case study, crystallization in the CsCl−CuCl₂−H₂O system is investigated. Large-sized crystals of CsCuCl₃ and Cs₃Cu₃Cl₈OH were produced from aqueous solutions within 4 and 16 h, respectively. We present two methods for growing large crystals: a guided approach that uses prior trials to pinpoint the temperatures for crystal formation, dissolution, and growth and an unguided approach without such trials. Our methodology serves as a framework for growing large crystals in emerging and unexplored solutions and is clearly aligned with evolving machine-vision approaches.