Reversed Crystal Growth

Abstract

In the last decade, a reversed growth route has been found in many crystal growth processes. In these systems, a single crystal does not develop from a single nucleus. The precursor molecules/ions or nanocrystallites aggregate into some large amorphous or polycrystalline particles. Multiple-nucleation on the surface of the amorphous particles or surface re-crystallization of the polycrystalline particles then takes place, forming a single crystal shell with a regular morphology. Finally, the crystallization extends from the surface to the core to form single crystals. This non-classical crystal growth route often results in some special morphologies, such as core-shell structures, hollow single crystals, sandwich structures, etc. This article gives a brief review of the research into reversed crystal growth and demonstrates that investigation of detailed mechanisms of crystal growth enables us to better understand the formation of many novel morphologies of the crystals. Some unsolved problems are also discussed.

Growth mechanism and microstructures of Cu2O/PVP spherulites

“…18 This surface recrystallisation of polycrystalline spheres seems to be quite common. 35 However, such a surface recrystallisation process was never found in any type of spherulites. The size of the unreduced Cu 2 O crystallites maintains at nanoscale even the reaction time was lengthened to 96 h.…”

Dual-Step Reduction of Copper and Formation Mechanism of Cu Pseudo-Icosahedral Microcrystals

“…The reversed crystal growth has been also found in metal oxides, carbonates, metal−organic frameworks, organic crystals, etc. 27 In fact, the formation of polycrystalline or non-crystalline aggregates is the first and crucial step of the reversed crystal growth mechanism. A similar phenomenon was observed in the present work.…”

Controllable Zeolite AST Crystallization: Between Classical and Reversed Crystal Growth

“…Reversed crystal growth (0.5≤ x ≤0.7) involves two steps: aggregation and crystallization [15a] . At the early stages, before crystallization starts, the synthesis precursors agglomerate together to form amorphous aggregates.…”

“…Aggregation of small species at the early stages of crystallization is presumably the most important step in reversed crystal growth [15a] . For example, multiple CaCO 3 nucleations can occur either on the surface of the aggregates or inside the aggregates, depending on the interaction strength between Ca 2+ and polymer additives [16] .…”

“…However, inhibition of the free growth of crystals does not explain aggregation at the early stages in other systems without adding additional agents. Generally, the synthesis system contains a mixture of inorganic and organic (structure‐directing agent, SDA) ions, and the interaction between them is expected to affect the initial aggregation [15a,18] . Despite this hypothesis, no direct evidence has been provided to confirm the relevance of this assumption.…”