INTERGROWTH SEGREGATION IN FAU-EMT ZEOLITE MATERIALS

Intergrowths of cubic (FAU) and hexagonal (EMT) structural phases in a number of faujasite-related zeolite materials have been studied using transmission electron microscopy, and high-resolution powder X-ray di ffraction. In Y, CSZ-1, CSZ-3, ZSM-2, ZSM-3, ZSM-20, ECR-35, ECR-30 an d EMC-2 materials, the FAU and EMT components segregate non-randomly i nto contiguous blocks. This segregation is most pronounced in ZSM-20 a nd ECR-35. ECR-30 and EMC-2 are both predominantly EMT framework mater ials, within which FAU intergrowths occur in clumps of 1, 2 or 3 layer s. No evidence is found for extended superlattice ordering of intergro wths. Intergrowth segregation acts to reduce both the configurational entropy associated with the stacking statistics and the elastic energy associated with coherency strain.