The orthorhombic/monoclinic transition in single crystals of zeolite ZSM-5 |
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| Affiliation: | 1. Soil Science and Agricultural Chemistry Group, Department of Plant Biology and Soil Science, Faculty of Sciences, University of Vigo, E-32004 Ourense, Spain;2. Department of Agroecology, Faculty of Sciences and Technology, Aarhus University, Blichers Allé 20, P.O. Box 50, DK-8830 Tjele, Denmark |
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| Abstract: | X-ray photographs of single crystals of zeolite H-ZSM-5 (Si11.96Al0.04H0.04O24) at different temperatures are presented. The reversible orthorhombic/monoclinic transition, previously observed with XRD and 29Si m.a.s. n.m.r. on powder samples of H-ZSM-5, is confirmed. Upon cooling, the orthorhombic H-ZSM-5 single crystal changes into an aggregate of monoclinic twin domains. The directions of a and c in the orthorhombic single crystal and in the monoclinic twinned crystal (a ≈ 90.5°) are identical. The deviation of α from 90° can be ascribed to a mutual shift of successive (010) pentasil layers along c, induced by a distortion or rotation of the T4 and T6 rings interconnecting the layers. The space group of the monoclinic phase most probably is P12n11. |
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