Structured diffuse scattering, displacive flexibility and polymorphism in Ba-hexacelsian |
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| Authors: | Y Tabira R L Withers Y Takéuchi F Marumo |
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| Institution: | (1) Research School of Chemistry, Australian National University Canberra, ACT, 0200 Australia Fax: (61) (2) 62490750 e-mail: withers@rsc.anu.edu.au, AU;(2) College of Humanities and Sciences, Nihon University 3-25-40, Sakurajosui, Setagayaku, Tokyo 156-8550 Japan, JP |
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| Abstract: | The results of a temperature-dependent electron diffraction study of the low frequency modes of distortion of Ba-hexacelsian
and their relationship to the α-β polymorphic phase transition therein are presented. Cs- and Rb-doped Ba-hexacelsian specimens
are also investigated. An extremely strong and characteristic diffuse intensity distribution in the form of polarized sheets
of diffuse intensity perpendicular to the <1 1 0> directions is found for the high temperature polymorph and the doped specimens.
The diffuse distribution appears to result from coupled tetrahedral rotation of <1 1 0> columns of corner-connected (Al,Si)O4 tetrahedra about the 0 0 1] axis (uncorrelated from column to column as a result of the positioning of the rotation axes).
Received: 25 January 1999 / Revised, accepted: 13 July 1999 |
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| Keywords: | Hexacelsian Polymorphism Diffuse distribution Dynamical disorder Correlated tetrahedral rotation |
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