Rigid unit modes dynamics in the molecular sieve material AlPO4-5

The web-like ring structure composed of corner-sharing tetrahedra in AlPO4-5 has received considerable attention over the years because its unusual topology enables entrapment and diffusion of guest molecules within the extended micropores1. Recent work on this molecular sieve reported clear evidence for strong sub-picosecond tetrahedral dynamics attributed to rigid-unit modes (RUMS). In order to preserve the bond-lengths during these motions, some chemical species undergo restricted rotational diffusion within relatively large volumes around their average lattice positions. These motions drive fluctuations in the effective pore-window sizes, potentially acting to filter absorption and diffusion of guest species. Here we report a quasi-elastic neutron scattering investigation of the dynamics over the temperature range 1.5 – 300 K using the PELICAN instrument. This is compared with ab initio molecular dynamics to gain a clear microscopic picture of the timescales of the entangled motions within the tetrahedra network.

Keywords

Topology, Molecules, Bond lengths, Diffusion, Absorption, Microstructure

Citation

Cortie, D. L., McBride, B. R., Mole, R. A., Withers, R., Yu, D., McIntyre, G., & Liu, Y. (2016). Rigid unit modes dynamics in the molecular sieve material AlPO4-5. Paper presented at 13th AINSE-ANBUG Neutron Scattering Symposium, Sydney, NSW, Australia, 29-30 November 2016.

URI

https://apo.ansto.gov.au/dspace/handle/10238/12110

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