Controllable Zeolite AST Crystallization: Between Classical and Reversed Crystal Growth. Issue 35 (3rd May 2022) - Yue, Qiudi
Abstract: Crystal growth mechanisms govern a wide range of properties of crystalline materials. Reversed crystal growth is one of the nonclassical mechanisms observed in many materials. However, the reversed crystallization starting from amorphous aggregates and the key factors driving this growth remain elusive. Here, we describe a characteristic model of reversed crystal growth representing the inner structure and crystallinity development of aggregates studied by microscopy and nano X‐ray computed tomography. By adjusting the synthesis conditions, the fundamental function of the structure‐directing agent, which determines the crystallization pathway, was revealed. As a result, the crystal growth mode can be "switched" from the classical route at a low ratio of SDA/framework elements to reversed growth at a high ratio. Our findings provide further insights into crystal growth control, which is crucial for improving synthesis protocols and designing various forms of crystalline materials. Abstract : A truly reversed crystal growth mode in which the crystallization starts at the surface of a spherically amorphous aggregate and then proceeds towards its center is described. The fundamental function of the structure‐directing agent (SDA) controlling the crystallization pathway is uncovered. Thus, the crystallization pathway can be "switched" between classical and reversed crystal growth by tuning the concentration of the SDA.