A coupled electron diffraction and rigid unit mode (RUM) study of the crystal chemistry of some zeotypic AlPO{sub 4} compounds

Journal Article · Thu Sep 15 00:00:00 EDT 2005 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2005.06.003· OSTI ID:20729069

Withers, Ray L ^[1]; Liu, Yun ^[1]

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1. Research School of Chemistry, Australian National University, Canberra, ACT 0200 (Australia)

Electron diffraction and lattice dynamical calculations are used to investigate the unit cells, space group symmetries and inherent displacive flexibility of the room-temperature average structures of AlPO{sub 4}-8, AlPO{sub 4}-16 and AlPO{sub 4}-tridymite. The zero-frequency rigid unit modes (RUMs) of the idealized high-symmetry polymorphs thereof are also investigated along with their relationship to the lower-temperature polymorphism of these zeotypic aluminophosphates. The clear presence of G+/-12c{sup *} satellite reflections in addition to the Bragg reflections (G) of the underlying Cmc2{sub 1} parent structure in the case of AlPO{sub 4}-8 shows that the true unit cell of the room-temperature polymorph has a doubled c-axis due to a condensed RUM mode. Structured diffuse scattering is also observed which can be related to the thermal excitation of RUM modes. In the case of AlPO{sub 4}-tridymite, a complex F1 triclinic polymorph is observed and related to soft RUM modes while, in the case of AlPO{sub 4}-16, a soft q=0 RUM mode is shown to be responsible for an observed phase transition in the case of the all SiO{sub 2} analogue of AlPO{sub 4}-16. A large number of additional zero-frequency RUM modes also exist in the case of AlPO{sub 4}-16.

• OSTI ID: 20729069
• Journal Information: Journal of Solid State Chemistry, Vol. 178, Issue 9; Other Information: DOI: 10.1016/j.jssc.2005.06.003; PII: S0022-4596(05)00252-5; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALUMINIUM PHOSPHATES
BRAGG REFLECTION
DIFFUSE SCATTERING
ELECTRON DIFFRACTION
EXCITATION
ORTHORHOMBIC LATTICES
PHASE TRANSFORMATIONS
SILICON OXIDES
SPACE GROUPS
TEMPERATURE RANGE 0273-0400 K