Intergrowth structure modelling in silicoaluminophosphate SAPO-18/34 family

• Published in: Microporous and mesoporous materials 2014-09, Vol.195, p.311-318
• Main Authors: Sławiński, Wojciech A., Wragg, David S., Akporiaye, Duncan, Fjellvåg, Helmer
• Format: Article
• Language: English
• Subjects: Crystal structure modelling; Intergrowth; SAPO; Stacking faults; XRD
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2014.04.024

[Display omitted] •We model the crystal structure of SAPO-18/34 intergrowth.•The two possible stacking fault types Displacement and Growth are described.•X-ray powder diffraction patterns were measured on high intergrowth SAPO-34.•A “defect-free” AlPO-18 sample also show some level of intergrowth.•A simple method for defect level estimation is proposed. We present a consistent model of the crystal structure of SAPO-18/34 family members. The model utilises two types of stacking fault: Displacement and Growth which have significantly different effects on the diffraction pattern. A series of powder diffraction patterns is calculated using the Discus software package. Changes in the level of intergrowth and stacking fault type strongly affect the calculated pattern. A series of patterns has been calculated to illustrate this. The structure of an intergrown SAPO-34 sample with 4.8% Si content is modelled and refined using Displacement stacking faults. An example of “defect-free” AlPO-18 (0% Si content member of SAPO-18/34 family) is then presented. Refinement of the model shows that even this contains a small amount of stacking faults. Finally, a simple method for defect level estimation is proposed based on FWHM ratios for selected Bragg reflections.