JMZ-11: A Set of Non-Stochastic Intergrowths in the CHA-GME System Featuring a "sfw-GME" Tail
Authors: Mervyn D. Shannon, Sanyuan Yang, Daniel Gilleland, Misbah Sarwar, Nicholas McNamara, Joseph Fedeyko and Alessandro Turrina (Johnson Matthey) and Alvaro Mayoral (University of Zaragoza)
JMZ-11 is a family of molecular sieves comprising intergrowths of cha and aft having an "sfw-GME tail". The "sfw-GME tail" can be visualised by electron microscopy and the intergrowth quantified by analysis using a Reichweite 2 DIFFaX model. The gme cavities providing the support framework for cavities larger than cha are implicit in the model but omitted in the descriptions.
DIFFaX modelling of CHA-GME intergrowths in the literature are based on the stacking of layers 5Å thick. These layers have a six ring on, say, the A site linked to another on, say, the B site. The stacking involves either a mirror 1.5Å above B site to yield ABBA…. or GME type stacking, or an inversion to yield ABBC…. or CHA type stacking. Structures in the literature appear to be either stochastic intergrowths of these layers, for example Babelite, or intergrowths of a limited number of cavity sizes such as SSZ-52.
JMZ-11 materials have a very large volume fraction occupied by cavities of the size of sfw or larger (the "sfw-GME tail") that are well represented by a monotonically decreasing distribution that follows the binomial representation. The proportions of cha and aft cavities do not conform to that distribution. A DIFFaX model with memory of the previous two layers known as Reichweite 2 provides good representation of the powder diffraction patterns. The starting point for estimation of the 4 independent parameters in the model is obtained from analysis of aberration-corrected STEM HAADF images.
The presentation will provide a description of the model, discuss examples of the family of structures and refer to the structure directing agents that give rise to them.