Complex screw dislocation core in zeolite MTW - Dr. Shengcai Zhu

OCTOBER 30, 2017

A group of scientists co-led by Dr. Shengcai Zhu of HPSTAR, investigated the evolution of hyper structure and screw dislocation for the framework material zeolite MTW, a useful industrial solid acid catalyst. They revealed that the complex screw dislocation core in zeolite MTW was composed by different crystal domains with different stacking vector. Their findings are published by recent issue of Angewandte Chemie International Edition (DOI:10.1002/anie.201704499).

Screw dislocation structures in crystals are an origin of symmetry breaking in a wide range of dense-phase crystals. Preparation of such analogous structures in framework-phase crystals is of great importance in zeolites but is still a challenge. On the basis of crystal-structure solving and model building, it was found that the two specific intergrowths in MTW zeolite produce this complex fractal and spiral structure. With the structurally determined parameters(spiral pitch h, screw angle θ, and spatial angle ψ) of Burgers circuit, the screw dislocation structure can be constructed by two different dimensional intergrowth sections. Thus, the reported complexity of various dimensions indiverse crystals can be unified.

“Such dislocation structures have been widely captured in dense-phase materials, such as metal oxides and alloy compounds, ceramics, carbon nanotubes, and even ice. Comparatively, in framework materials, the real nature of screw dislocation structure remains elusive”, said Lei Wang, one of the study’s two lead authors. “In the past, screw dislocation was considered in existence in the framework materials. However, via the high resolution TEM of this work, we renew the knowledge of screw growth on the framework materials”.

“The diverse Si-O bonds on the framework materials make the screw dislocation extremely complex. Revealing the atomistic structure of screw dislocation in zeolite MTW will have a profound impact on the researches involving framework materials”, said Dr. Sheng-Cai Zhu. “Via the 3D atomic level structure, composed by twin structure andscrew dislocation structures, which perfect interpret the observation ofexperiment”.

Caption: Stacking faults, screw dislocation and model of zeolite MTW.

螺旋位错核一直是物理，材料领域研究的的热点课题之一。在早前的报道中螺旋位错核一直是在致密相材料中被揭示，而在骨架材料（Zeolites,MOFs, COFs）中则鲜有报道。近期，北京高压科学研究中心的博士后朱升财和上海复旦大学的唐颐教授研究小组携手合作，采用高分辨透射电镜及高分辨模拟精细结构对低对称性的MTW沸石进行了一系列的研究。该研究不仅从丰富的实验层面和晶体理论分析，对MTW沸石提出了新的空旷相螺旋位错核结构，更进一步结合文献结果，对不同相态的和不同空间对称性的沸石晶体材料的螺旋生长发展了较为统一的理论描述。这一研究结果发表《Angewandte ChemieInternational Edition》。